Judicial Opinion 129

Opinion 129 addresses the status of Firmicutes corrig. Gibbons and Murray 1978 (Approved Lists 1980). The name has the category 'division' and was included in the Approved Lists of Bacterial Names, although that category had previously been removed from the International Code of Nomenclature of Bacteria (1975 revision onwards). When the category 'phylum' was introduced into the International Code of Nomenclature of Prokaryotes (ICNP) in 2021, equivalence between 'phylum' and 'division' was not stipulated. Since the definition of the taxonomic categories and their relative order is one of the principal tasks of every code of nomenclature, the inclusion of Firmicutes corrig. Gibbons and Murray 1978 in the Approved Lists was an error. The name is either not validly published or illegitimate because its category is not covered by the ICNP. If Firmicutes corrig. Gibbons and Murray 1978 (Approved Lists 1980) was a validly published phylum name, it would be illegitimate because it would contravene Rule 8, which does not permit any deviation from the requirement to derive a phylum name from the name of the type genus. Since Firmicutes corrig. Gibbons and Murray 1978 is also part of a 'misfitting megaclassification' recognized in Opinion 128, the name is rejected, without any pre-emption regarding a hypothetically validly published name Firmicutes at the rank of phylum. Gracilicutes Gibbons and Murray 1978 (Approved Lists 1980) and Anoxyphotobacteriae Gibbons and Murray 1978 (Approved Lists 1980) are also rejected. The validly published phylum names have a variety of advantages over their not validly published counterparts and cannot be replaced with ad hoc names suggested in the literature. To ease the transition, it is recommended to mention the not validly published phylum names which strongly deviate in spelling from their validly published counterparts along with the latter in publications during the next years.

Multilocus sequence and phenotypic analysis of Pectobacterium and Dickeya type strains for identification of soft rot Pectobacteriaceae from symptomatic potato stems and tubers in Pennsylvania

Outbreaks of potato blackleg and soft rot caused by Pectobacterium species and more recently Dickeya species across the U.S. mid-Atlantic region have caused yield loss due to poor emergence as well as losses from stem and tuber rot. To develop management strategies for soft rot diseases, we must first identify which members of the soft rot Pectobacteriaceae are present in regional potato plantings. However, the rapidly expanding number of soft rot Pectobacteriaceae species and the lack of readily available comparative data for type strains of Pectobacterium and Dickeya hinder quick identification. This manuscript provides a comparative analysis of soft rot Pectobacteriaceae and a comprehensive comparison of type strains from this group using rep-PCR, MLSA and 16S sequence analysis, as well as phenotypic and physiological analyses using Biolog GEN III plates. These data were used to identify isolates cultured from symptomatic potato stems collected between 2016 and 2018. The isolates were characterized for phenotypic traits and by sequence analysis to identify the bacteria from potatoes with blackleg and soft rot symptoms in Pennsylvania potato fields. In this survey, P. actinidiae, P. brasiliense, P. polonicum, P. polaris, P. punjabense, P. parmentieri, and P. versatile were identified from Pennsylvania for the first time. Importantly, the presence of P. actinidiae in Pennsylvania represents the first report of this organism in the U.S. As expected, P. carotorvorum and D. dianthicola were also isolated. In addition to a resource for future work studying the Dickeya and Pectobacterium associated with potato blackleg and soft rot, we provide recommendations for future surveys to monitor for quarantine or emerging soft rot Pectobacteriace regionally.

Manipulating Agaricus bisporus developmental patterns by passaging microbial communities in complex substrates

IMPORTANCE

Agaricus bisporus is an economically important edible mushroom and manipulating its developmental patterns is crucial for maximizing yield and quality. One of the potential strategies for achieving such a goal is passaging microbial communities in compost or casing. The current study demonstrated that passaging substrates develop enriched microbial communities, and after a few passages, certain levels of changes in mushroom developmental patterns (the timing of fruiting bodies formation) were observed as well as shifts in the bacterial communities. Overall, a better understanding of the complex interactions between microorganisms present in the cultivation system may help farmers and researchers to develop more efficient and sustainable cultivation practices that can both benefit the environment and human health.

Judicial Opinion 128

Judicial Opinion 128 addresses nomenclatural issues related to the names of classes validly published under the International Code of Nomenclature of Prokaryotes. It is confirmed that the common ending -proteobacteria of some class names is not indicative of a joint taxonomic or phylogenetic placement; that the nomenclatural type of Mollicutes Edward and Freundt 1967 (Approved Lists 1980) is Mycoplasmatales Freundt 1955 (Approved Lists 1980); and that the placement of a name on the list of rejected names does not imply that another name with the same spelling but a distinct rank is also placed on that list. The names at the rank of class Anoxyphotobacteria (Gibbons and Murray 1978) Murray 1988, Archaeobacteria Murray 1988, Bacteria Haeckel 1894 (Approved Lists 1980), Firmibacteria Murray 1988, Microtatobiotes Philip 1956 (Approved Lists 1980), Oxyphotobacteria (ex Gibbons and Murray 1978) Murray 1988, Photobacteria Gibbons and Murray 1978 (Approved Lists 1980), Proteobacteria Stackebrandt et al. 1988, Schizomycetes Nägeli 1857 (Approved Lists 1980), Scotobacteria Gibbons and Murray 1978 (Approved Lists 1980) are placed on the list of rejected names. For three common nominative singular suffixes of genus names their genitive singular and nominative plural forms are confirmed: -bacter (-bacteris, -bacteres); -fex (-ficis, -fices); and -genes (-genis, -genes). The class names Aquificae Reysenbach 2002, Chrysiogenetes Garrity and Holt 2002, Chthonomonadetes Lee et al. 2011, Gemmatimonadetes Zhang et al. 2003, Opitutae Choo et al. 2007 and Verrucomicrobiae Hedlund et al. 1998 are orthographically corrected to Aquificia, Chrysiogenia, Chthonomonadia, Gemmatimonadia, Opitutia and Verrucomicrobiia, respectively.

Guidelines for interpreting the International Code of Nomenclature of Prokaryotes and for preparing a Request for an Opinion

In this paper the Judicial Commission provides general guidance for interpreting the International Code of Nomenclature of Prokaryotes (ICNP) and specific assistance to authors, reviewers and editors of a Request for an Opinion, or of other suggestions related to the ICNP. The role of the Judicial Commission is recapitulated, particularly with respect to the processing of such Requests. Selected kinds of nomenclature-related proposals are discussed that are unsuitable as the basis for a Request. Particular emphasis is put on Requests for placing names or epithets on the list of nomina rejicienda, and a dichotomous identification key is provided to guide potential authors of a Request that targets the name of a species or subspecies because of issues with its type strain. To this end, the criteria for the valid publication of such names under the ICNP are revisited. Aspects of other kinds of Requests are also addressed. The study is based on a comprehensive review of all Judicial Opinions issued since the publication of the Approved Lists in 1980. One goal of this paper is to assist potential authors in deciding whether their concern should be the subject of a Request, and if so, in composing it with the greatest chance of success. It is also clarified how to obtain additional help regarding nomenclature-related issues.

Ewingella americana: An Emerging Multifaceted Pathogen of Edible Mushrooms

Mycopathogenic bacteria play a pivotal role in the productivity of edible mushrooms grown under controlled conditions. In this study, we carried out a comprehensive farm survey and sampling (2018 to 2021) on button mushroom (Agaricus bisporus) farms in 15 provinces in Iran to monitor the status of bacterial pathogens infecting the crop. Mycopathogenic bacterial strains were isolated from pins, stems, and caps, as well as the casing layer on 38 mushroom farms. The bacterial strains incited symptoms on mushroom caps ranging from faint discoloration to dark brown and blotch of the inoculated surfaces. Among the bacterial strains inciting disease symptoms on bottom mushroom, 40 were identified as Ewingella americana based on biochemical assays and phylogeny of 16S rRNA and the gyrB gene. E. americana strains differed in their aggressiveness on mushroom caps and stipes, where the corresponding symptoms ranged from deep yellow to dark brown. In the phylogenetic analyses, all E. americana strains isolated in this study were clustered in a monophyletic clade closely related to the nonpathogenic and environmental strains of the species. BOX-PCR-based fingerprinting revealed intraspecific diversity. Using the cutoff level of 73 to 76% similarity, the strains formed six clusters. A chronological pattern was observed, where the strains isolated in 2018 were differentiated from those isolated in 2020 and 2021. Taken together, due to the multifaceted nature of the pathogen, such a widespread occurrence of E. americana on mushroom farms in Iran could be an emerging threat for the mushroom industry in the country.

Judicial Opinions 123-127

Opinion 123 places the epithet of the name Aeromonas punctata on the list of rejected epithets and clarifies the citation of authors of selected names within the genus Aeromonas. Opinion 124 denies the request to place Borreliella on the list of rejected names because the request is based on a misinterpretation of the Code, which is clarified. There are alternative ways to solve the perceived problem. Opinion 125 denies the request to place Lactobacillus fornicalis on the list of rejected names because the provided information does not yield a reason for rejection. Opinion 126 denies the request to place Prolinoborus and Prolinoborus fasciculus on the list of rejected names because a relevant type strain deposit was not examined. Opinion 127 grants the request to assign the strain deposited as ATCC 4720 as the type strain of Agrobacterium tumefaciens, thereby correcting the Approved Lists. These Opinions were ratified by the voting members of the International Committee on Systematics of Prokaryotes.

Comparative Genomic Analysis of the Lettuce Bacterial Leaf Spot Pathogen, Xanthomonas hortorum pv. vitians, to Investigate Race Specificity

Bacterial leaf spot (BLS) of lettuce caused by Xanthomonas hortorum pv. vitians (Xhv) was first described over 100 years ago and remains a significant threat to lettuce cultivation today. This study investigated the genetic relatedness of the Xhv strains and the possible genetic sources of this race-specific pathogenicity. Whole genome sequences of eighteen Xhv strains representing the three races, along with eight related Xanthomonas strains, were included in the analysis. A maximum likelihood phylogeny based on concatenated whole genome SNPs confirmed previous results describing two major lineages of Xhv strains. Gene clusters encoding secretion systems, secondary metabolites, and bacteriocins were assessed to identify putative virulence factors that distinguish the Xhv races. Genome sequences were mined for effector genes, which have been shown to be involved in race specificity in other systems. Two effectors identified in this study, xopAQ and the novel variant xopAF2, were revealed as possible mediators of a gene-for-gene interaction between Xhv race 1 and 3 strains and wild lettuce Lactuca serriola ARM-09-161-10-1. Transposase sequence identified downstream of xopAF2 and prophage sequence found nearby within Xhv race 1 and 3 insertion sequences suggest that this gene may have been acquired through phage-mediated gene transfer. No other factors were identified from these analyses that distinguish the Xhv races.

Clarifying the taxonomy of the causal agent of bacterial leaf spot of lettuce through a polyphasic approach reveals that Xanthomonas cynarae Trébaol et al. 2000 emend. Timilsina et al. 2019 is a later heterotypic synonym of Xanthomonas hortorum Vauterin et al. 1995

Assessment of the taxonomy and diversity of Xanthomonas strains causing bacterial leaf spot of lettuce (BLSL), commonly referred to as Xanthomonas campestris pv. vitians, has been a long-lasting issue which held back the global efforts made to understand this pathogen. In order to provide a sound basis essential to its study, we conducted a polyphasic approach on strains obtained through sampling campaigns or acquired from collections. Results of a multilocus sequence analysis crossed with phenotypic assays revealed that the pathotype strain does not match the description of the nomenspecies provided by Brown in 1918. However, strain LMG 938=CFBP 8686 does fit this description. Therefore, we propose that it replaces LMG 937=CFBP 2538 as pathotype strain of X. campestris pv. vitians. Then, whole-genome based phylogenies and overall genome relatedness indices calculated on taxonomically relevant strains exhibited the intermediate position of X. campestris pv. vitians between closely related species Xanthomonas hortorum and Xanthomonas cynarae. Phenotypic profiles characterized using Biolog microplates did not reveal stable diagnostic traits legitimizing their distinction. Therefore, we propose that X. cynarae Trébaol et al. 2000 emend. Timilsina et al. 2019 is a later heterotypic synonym of X. hortorum, to reclassify X. campestris pv. vitians as X. hortorum pv. vitians comb. nov. and to transfer X. cynarae pathovars in X. hortorum as X. hortorum pv. cynarae comb. nov. and X. hortorum pv. gardneri comb. nov. An emended description of X. hortorum is provided, making this extended species a promising model for the study of Xanthomonas quick adaptation to different hosts.

Transfer of Xanthomonas campestris pv. arecae and X. campestris pv. musacearum to X. vasicola (Vauterin) as X. vasicola pv. arecae comb. nov. and X. vasicola pv. musacearum comb. nov. and Description of X. vasicola pv. vasculorum pv. nov

We present an amended description of the bacterial species Xanthomonas vasicola to include the causative agent of banana Xanthomonas wilt, as well as strains that cause disease on Areca palm, Tripsacum grass, sugarcane, and maize. Genome-sequence data reveal that these strains all share more than 98% average nucleotide with each other and with the type strain. Our analyses and proposals should help to resolve the taxonomic confusion that surrounds some of these pathogens and help to prevent future use of invalid names.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Bacterial Brown Pit, a New Disease of Edible Mushrooms Caused by Mycetocola sp

From September to December 2018, commercial button mushroom (Agaricus bisporus) farms in central Iran were surveyed to monitor the causal agent(s) of browning and blotch symptoms on mushroom caps. In addition to dozens of pseudomonads (i.e., Pseudomonas tolaasii and Pseudomonas reactans), six slow-growing gram-positive bacterial strains were isolated from blotched mushroom caps. These bacteria presented as creamy white, circular, smooth, nonfluorescent, and shiny colonies with whole margins resembling members of Microbacteriaceae (Actinobacteria). All of the actinobacterial strains were aggressively pathogenic on cut cap surface of two edible mushrooms (i.e., A. bisporus and Pleurotus eryngii), inducing brown pit symptoms 48 h postinoculation. The strains did not induce symptoms on the vegetables tested (i.e., carrot, cucumber, and potato), and they did not affect the growth of mycelium of tested plant-pathogenic fungi (i.e., Acremonium sp., Fusarium spp., and Phytopythium sp.). Phylogeny of 16S ribosomal RNA and multilocus sequence analysis of six housekeeping genes (i.e., atpD, dnaK, gyrB, ppK, recA, and rpoB) revealed that the bacterial strains belong to the actinobacterial genus Mycetocola spp., whereas the species status of the strains remains undetermined. Mushroom-associated Mycetocola species were previously reported to be capable of detoxifying tolaasin, a toxin produced by P. tolaasii, whereas the strains isolated in this study did not show tolaasin detoxification activities. Altogether, this is the first report of a mushroom disease caused by an actinobacterial species, and "bacterial brown pit" was assigned as the common name of the disease.

Identification of Pseudomonas Isolates Associated With Bacterial Canker of Stone Fruit Trees in the Western Cape, South Africa

Bacterial canker is a common bacterial disease of stone fruit trees. The causal agents responsible for the disease include several pathovars in Pseudomonas syringae sensu lato and newly described Pseudomonas species. Pseudomonad strains were isolated from symptomatic stone fruit trees, namely apricot, peach, and plum trees cultivated in spatially separated orchards in the Western Cape. A polyphasic approach was used to identify and characterize these strains. Using a multilocus sequence typing approach of four housekeeping loci, namely cts, gapA, gyrB, and rpoD, the pseudomonad strains were delineated into two phylogenetic groups within P. syringae sensu lato: P. syringae sensu stricto and Pseudomonas viridiflava. These results were further supported by LOPAT diagnostic assays and analysis of clades in the rep-PCR dendrogram. The pseudomonad strains were pathogenic on both apricot and plum seedlings, indicative of a lack of host specificity between Pseudomonas strains infecting Prunus spp. This is a first report of P. viridiflava isolated from plum trees showing symptoms of bacterial canker. P. viridiflava is considered to be an opportunistic pathogen that causes foliar diseases of vegetable crops, fruit trees, and aromatic herbs, and thus the isolation of pathogenic P. viridiflava from twigs of plum trees showing symptoms of bacterial canker suggests that this bacterial species is a potentially emerging stem canker pathogen of stone fruit trees in South Africa.

100 Years Since Tolaas: Bacterial Blotch of Mushrooms in the 21st Century

Among the biotic constraints of common mushroom (Agaricus bisporus) production, bacterial blotch is considered the most important mushroom disease in terms of global prevalence and economic impact. Etiology and management of bacterial blotch has been a major concern since its original description in 1915. Although Pseudomonas tolaasii is thought to be the main causal agent, various Pseudomonas species, as well as organisms from other genera have been reported to cause blotch symptoms on mushroom caps. In this review, we provide an updated overview on the etiology, epidemiology, and management strategies of bacterial blotch disease. First, diversity of the causal agent(s) and utility of high throughput sequencing-based approaches in the precise characterization and identification of blotch pathogen(s) is explained. Further, due to the limited options for use of conventional pesticides in mushroom farms against blotch pathogen(s), we highlight the role of balanced threshold of relative humidity and temperature in mushroom farms to combat the disease in organic and conventional production. Additionally, we discuss the possibility of the use of biological control agents (either antagonistic mushroom-associated bacterial strains or bacteriophages) for blotch management as one of the sustainable approaches for 21^st century agriculture. Finally, we aim to elucidate the association of mushroom microbiome in cap development and productivity on one hand, and blotch incidence/outbreaks on the other hand.

Inference of Convergent Gene Acquisition Among Pseudomonas syringae Strains Isolated From Watermelon, Cantaloupe, and Squash

Pseudomonas syringae sensu stricto (phylogroup 2; referred to as P. syringae) consists of an environmentally ubiquitous bacterial population associated with diseases of numerous plant species. Recent studies using multilocus sequence analysis have indicated the clonal expansion of several P. syringae lineages, located in phylogroups 2a and 2b, in association with outbreaks of bacterial spot disease of watermelon, cantaloupe, and squash in the United States. To investigate the evolutionary processes that led to the emergence of these epidemic lineages, we sequenced the genomes of six P. syringae strains that were isolated from cucurbits grown in the United States, Europe, and China over a period of more than a decade, as well as eight strains that were isolated from watermelon and squash grown in six different Florida counties during the 2013 and 2014 seasons. These data were subjected to comparative analyses along with 42 previously sequenced genomes of P. syringae stains collected from diverse plant species and environments available from GenBank. Maximum likelihood reconstruction of the P. syringae core genome revealed the presence of a hybrid phylogenetic group, comprised of cucurbit strains collected in Florida, Italy, Serbia, and France, which emerged through genome-wide homologous recombination between phylogroups 2a and 2b. Functional analysis of the recombinant core genome showed that pathways involved in the ATP-dependent transport and metabolism of amino acids, bacterial motility, and secretion systems were enriched for recombination. A survey of described virulence factors indicated the convergent acquisition of several accessory type 3 secreted effectors (T3SEs) among phylogenetically distinct lineages through integrative and conjugative element and plasmid loci. Finally, pathogenicity assays on watermelon and squash showed qualitative differences in virulence between strains of the same clonal lineage, which correlated with T3SEs acquired through various mechanisms of horizontal gene transfer (HGT). This study provides novel insights into the interplay of homologous recombination and HGT toward pathogen emergence and highlights the dynamic nature of P. syringae sensu lato genomes.

Genome-based evolutionary history of Pseudomonas spp

Pseudomonas is a large and diverse genus of Gammaproteobacteria. To provide a framework for discovery of evolutionary and taxonomic relationships of these bacteria, we compared the genomes of type strains of 163 species and 3 additional subspecies of Pseudomonas, including 118 genomes sequenced herein. A maximum likelihood phylogeny of the 166 type strains based on protein sequences of 100 single-copy orthologous genes revealed thirteen groups of Pseudomonas, composed of two to sixty three species each. Pairwise average nucleotide identities and alignment fractions were calculated for the data set of the 166 type strains and 1224 genomes of Pseudomonas available in public databases. Results revealed that 394 of the 1224 genomes were distinct from any type strain, suggesting that the type strains represent only a fraction of the genomic diversity of the genus. The core genome of Pseudomonas was determined to contain 794 genes conferring primarily housekeeping functions. The results of this study provide a phylogenetic framework for future studies aiming to resolve the classification and phylogenetic relationships, identify new gene functions and phenotypes, and explore the ecological and metabolic potential of the Pseudomonas spp.

Genetic Diversity and Virulence of Wheat and Barley Strains of Xanthomonas translucens from the Upper Midwestern United States

Bacterial leaf streak (BLS) of wheat and barley, caused by Xanthomonas translucens pv. undulosa and X. translucens pv. translucens, has been of growing concern in small grains production in the Upper Midwestern United States. To optimize disease resistance breeding, a greater awareness is needed of the pathovars and genetic diversity within the pathogens causing BLS in the region. Multilocus sequencing typing (MLST) and analysis (MLSA) of four common housekeeping genes (rpoD, dnaK, fyuA, and gyrB) was used to evaluate the genetic diversity of 82 strains of X. translucens isolated between 2006 and 2013 from wheat, barley, rye, and intermediate wheatgrass. In addition, in planta disease assays were conducted on 75 strains to measure relative virulence in wheat and barley. All strains were determined by MLSA to be related to X. translucens pv. undulosa and X. translucens pv. translucens. Clustering of strains based on Bayesian, network, and minimum spanning trees correlated with relative virulence levels in inoculated wheat and barley. Thus, phylogeny based on rpoD, dnaK, fyuA, and gyrB correlated with host of isolation and was an effective means for predicting virulence of strains belonging to X. translucens pv. translucens and X. translucens pv. undulosa.

Multilocus Sequence Typing of Strains of Bacterial Spot of Lettuce Collected in the United States

Studies on genetic diversity and recombination in bacterial pathogens are providing a better understanding of the mechanisms shaping bacterial diversity, which can affect disease control. Xanthomonas campestris pv. vitians, causal agent of bacterial leaf spot of lettuce, is a threat to the worldwide lettuce industry. We examined the genetic variation within a sample of 83 strains from California, Florida, and Ohio using multilocus sequence typing of six housekeeping genes, totaling 2.7 kb. Additionally, polymorphism in two virulence-related genes, hrpB2 and a putative glycosyl hydrolase, were examined. Based on housekeeping genes, we found three genetic groups of strains that were all able to induce the disease. These included strains collected from weeds and irrigation water that had haplotypes identical to strains from diseased lettuce. High linkage disequilibrium across the sequenced loci indicates that the pathogen is predominantly clonal but recombination has contributed to the observed sequence variation. Although there was significant genetic variation in X. campestris pv. vitians within and among sampled states, identical haplotypes were observed across all three states. This finding suggests that seedborne inoculum may contribute to the diversity of X. campestris pv. vitians in the United States. Knowledge of the genetic structure of the pathogen may be used for developing resistant lettuce varieties.

Angular Leaf Spot of Cucurbits is Associated With Genetically Diverse Pseudomonas syringae Strains

Angular leaf spot of cucurbits is generally considered to be caused by Pseudomonas syringae pv. lachrymans. It has a worldwide distribution and has been observed to emerge sporadically under humid and wet conditions. Reports of multiple P. syringae pathovars associated with the disease and lack of molecular analysis has left the true diversity of populations in the United States unclear. In this study, we collected 27 P. syringae strains causing foliar lesions and blighting on watermelon, cantaloupe, and squash in Florida, Georgia, and California over several years. Strains were fluorescent on King's medium B agar and displayed the typical phenotypic and biochemical characteristics of P. syringae. P. syringae pv. lachrymans is a member of genomospecies 2. However, the genetic profiles obtained through both MLSA (gyrB, rpoD, gapA, and gltA) and BOX-PCR (BOXA1R) identified 26 of the P. syringae strains to be distributed among three clades within genomospecies 1, and phylogenetically distinct from genomospecies 2 member P. syringae pv. lachrymans. A novel MLSA haplotype of the pathogen common to all states and cucurbit hosts was identified. Considerable genetic diversity among P. syringae strains infecting cucurbits is associated with the same disease, and reflects the larger ecological diversity of P. syringae populations from genomospecies 1.

The U.S. Culture Collection Network Lays the Foundation for Progress in Preservation of Valuable Microbial Resources

The U.S. Culture Collection Network was formed in 2012 by a group of culture collection scientists and stakeholders in order to continue the progress established previously through efforts of an ad hoc group. The network is supported by a Research Coordination Network grant from the U.S. National Science Foundation (NSF) and has the goals of promoting interaction among collections, encouraging the adoption of best practices, and protecting endangered or orphaned collections. After prior meetings to discuss best practices, shared data, and synergy with genome programs, the network held a meeting at the U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) National Center for Genetic Resources Preservation (NCGRP) in Fort Collins, Colorado in October 2015 specifically to discuss collections that are vulnerable because of changes in funding programs, or are at risk of loss because of retirement or lack of funding. The meeting allowed collection curators who had already backed up their resources at the USDA NCGRP to visit the site, and brought collection owners, managers, and stakeholders together. Eight formal collections have established off-site backups with the USDA-ARS, ensuring that key material will be preserved for future research. All of the collections with backup at the NCGRP are public distributing collections including U.S. NSF-supported genetic stock centers, USDA-ARS collections, and university-supported collections. Facing the retirement of several pioneering researchers, the community discussed the value of preserving personal research collections and agreed that a mechanism to preserve these valuable collections was essential to any future national culture collection system. Additional input from curators of plant and animal collections emphasized that collections of every kind face similar challenges in developing long-range plans for sustainability.

First Report of Bacterial Blight of Crucifers Caused by Pseudomonas cannabina pv. alisalensis in Minnesota on Arugula (Eruca vesicaria subsp. sativa)

In 2011, bacterial blight of arugula (Eruca vesicaria subsp. sativa; cv. Roquette) was observed in organically grown plants under overhead irrigation in a field near Delano, MN. Approximately 80 to 100% of each planting was affected, with greater rates of infection occurring after periods of high humidity. Small, water-soaked, angular spots apparent on both sides of the leaves comprised the initial symptoms, which sometimes expanded and coalesced. Lesions maintained a dark water-soaked appearance or dried and turned a brown/tan color. Additionally, some lesions were outlined by a purple margin. Blue-green fluorescent pseudomonads were isolated consistently on King's Medium B agar (KMB) from symptomatic leaf tissue surface-disinfested with sodium hypochlorite (0.525%). The isolates nucleated ice and produced levan. Isolates were oxidase and arginine dihydrolase negative. They did not rot potato slices but did induce a hypersensitive reaction in tobacco (Nicotiana tabacum cv. Samsun). These data indicated that the bacteria belonged to Lelliott's LOPAT group 1 (2). DNA fragment banding patterns generated by amplifying DNA of the arugula isolates using repetitive extragenic palindromic sequence-polymerase chain reaction (rep-PCR) and the BOX A1R primer were identical and nearly identical to the banding patterns of the Pseudomonas cannabina pv. alisalensis (formerly P. syringae pv. alisalensis) (1) strain (CFBP1637) and the pathotype strain (CFBP 6866^PT), respectively. Pathogenicity was confirmed on the arugula cv. My Way in two independent experiments, each with three replicate plants per treatment. Four isolates were grown on KMB for 48 h at 27°C, suspended in 0.01M potassium phosphate buffer (pH 7.0), and adjusted to 0.6 optical density at 600 nm (approximately 1 × 10⁸ CFU/ml). Five- to six-week old plants were spray-inoculated until run-off, incubated in a humidity chamber for 48 h, and then placed in a greenhouse at 20 to 25°C for symptom development. For negative and positive control treatments, a similar number of plants each were sprayed with sterile buffer or P. cannabina pv. alisalensis strains CFBP1637 and CFBP 6866^PT, respectively. Water-soaked and brown/tan lesions similar to the original symptoms appeared on plants inoculated with the arugula isolates and P. cannabina pv. alisalensis strains 7 to 14 days postinoculation. No symptoms developed on plants treated with sterile buffer. The bacterial strains re-isolated from surface-disinfested symptomatic tissue were identical by rep-PCR to the isolates used to inoculate the plants, thus, confirming Koch's postulates. Identical replicated experiments conducted on broccoli raab indicated that the arugula isolates were also pathogens of broccoli raab (Brassica rapa subsp. rapa, the original host from which P. cannabina pv. alisalensis was isolated). To our knowledge, this is the first report of bacterial blight of crucifers caused by P. cannabina pv. alisalensis in Minnesota. Arugula germplasm is being evaluated for resistance to this pathogen as an acceptable management method for organic cropping systems. References: (1) C. T. Bull et al. Syst. Appl. Microbiol. 33:105, 2010. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

Host Genotype and Hypersensitive Reaction Influence Population Levels of Xanthomonas campestris pv. vitians in Lettuce

Dynamics of population sizes of Xanthomonas campestris pv. vitians inoculated onto or into lettuce leaves were monitored on susceptible and resistant cultivars. In general, population growth was greater for susceptible (Clemente, Salinas 88, Vista Verde) than resistant (Batavia Reine des Glaces, Iceberg, Little Gem) cultivars. When spray-inoculated or infiltrated, population levels of X. campestris pv. vitians were consistently significantly lower on Little Gem than on susceptible cultivars, while differences in the other resistant cultivars were not consistently statistically significant. Populations increased at an intermediate rate on cultivars Iceberg and Batavia Reine des Glaces. There were significant positive correlations between bacterial concentration applied and disease severity for all cultivars, but bacterial titer had a significantly greater influence on disease severity in the susceptible cultivars than in Little Gem and an intermediate influence in Iceberg and Batavia Reine des Glaces. Infiltration of X. campestris pv. vitians strains into leaves of Little Gem resulted in an incompatible reaction, whereas compatible reactions were observed in all other cultivars. It appears that the differences in the relationship between population dynamics for Little Gem and the other cultivars tested were due to the hypersensitive response in cultivar Little Gem. These findings have implications for disease management and lettuce breeding because X. campestris pv. vitians interacts differently with cultivars that differ for resistance mechanisms.

Practical benefits of knowing the enemy: modern molecular tools for diagnosing the etiology of bacterial diseases and understanding the taxonomy and diversity of plant-pathogenic bacteria

Knowing the identity of bacterial plant pathogens is essential to strategic and sustainable disease management in agricultural systems. This knowledge is critical for growers, diagnosticians, extension agents, and others dealing with crops. However, such identifications are linked to bacterial taxonomy, a complicated and changing discipline that depends on methods and information that are often not used by those who are diagnosing field problems. Modern molecular tools for fingerprinting and sequencing allow for pathogen identification in the absence of distinguishing or conveniently tested phenotypic characteristics. These methods are also useful in studying the etiology and epidemiology of phytopathogenic bacteria from epidemics, as was done in numerous studies conducted in California's Salinas Valley. Multilocus and whole-genome sequence analyses are becoming the cornerstones of studies of microbial diversity and bacterial taxonomy. Whole-genome sequence analysis needs to become adequately accessible, automated, and affordable in order to be used routinely for identification and epidemiology. The power of molecular tools in accurately identifying bacterial pathogenesis is therefore of value to the farmer, diagnostician, phytobacteriologist, and taxonomist.

The inheritance of resistance to bacterial leaf spot of lettuce caused by Xanthomonas campestris pv. vitians in three lettuce cultivars

Lettuce yields can be reduced by the disease bacterial leaf spot (BLS) caused by the pathogen Xanthomonas campestris pv. vitians (Xcv) and host resistance is the most feasible method to reduce disease losses. The cultivars La Brillante, Pavane and Little Gem express an incompatible host-pathogen interaction as a hypersensitive response (HR) to California strains of Xcv resulting in resistance. Little was known about the inheritance of resistance; however, resistance to other lettuce pathogens is often determined by resistance gene candidates (RGCs) encoding nucleotide-binding leucine-rich repeat (NB-LRR) proteins. Therefore, we determined the inheritance of BLS resistance in the cultivars La Brillante, Little Gem and Pavane and mapped it relative to RGCs. The reaction to Xcv was analyzed in nine F1, F2 and recombinant inbred line populations of lettuce from HR×compatible or HR×HR crosses. The HR in La Brillante, Pavane and Little Gem is conditioned by single dominant genes, which are either allelic or closely linked genes. The resistance gene in La Brillante was designated Xanthomonas resistance 1 (Xar1) and mapped to lettuce linkage group 2. Xar1 is present in a genomic region that contains numerous NB-LRR encoding RGCs and functional pathogen resistance loci in the RGC2 family. The Xar1 gene confers a high level of BLS resistance in the greenhouse and field that can be introgressed into commercial lettuce cultivars to reduce BLS losses using molecular markers.

Novel primers and PCR protocols for the specific detection and quantification of Sphingobium suberifaciens in situ

The pathogen causing corky root on lettuce, Sphingobium suberifaciens, is recalcitrant to standard epidemiological methods. Primers were developed from 16S rDNA sequences to be useful for the specific detection and quantification of S. suberifaciens. Quantitative PCR (qPCR) protocols specifically amplified DNA from the type strain of S. suberifaciens (LMG 17323) and other members of this species but not from other members of the Sphingomonadaceae. The detection limit was as little as 100 fg DNA (equivalent to 2 × 10(2) cells) in the qPCR. Detection was successful from soils inoculated with as little as 1 × 10(3) CFU/g soil. DNA isolated from naturally infested soils and diseased lettuce roots was amplified and sequenced fragments were identical or nearly identical to 16S rDNA sequences from S. suberifaciens. In growth chamber experiments, there was a positive correlation between disease severity and S. suberifaciens population levels in roots and soil, as detected by qPCR. Detection levels were below population levels of the pathogen necessary for disease development.

Pseudomonas Blight Caused by Pseudomonas syringae on Raspberry in California

In February 2013 in coastal California (Santa Cruz County), plantings of red raspberry (Rubus idaeus var. strigosus) exhibited symptoms of a previously undocumented disease. Initial symptoms were small (less than 5 mm wide), angular, water-soaked lesions on leaf and petiole tissues of recently emerged foliage. Lesions were observable from both adaxial and abaxial leaf surfaces. As disease progressed, lesions enlarged and coalesced, resulting in significant dark brown to black blighting of the foliage. The foliage of severely affected plants was stunted and wilted. The disease affected 5 ha and incidence was approximately 30%. Cream-colored bacterial colonies were isolated from surface disinfested symptomatic tissue that was macerated and streaked onto King's medium B (KMB) and sucrose peptone agar (SPA). Fungi were not recovered from any tissue that was surface disinfested and placed into acidified potato dextrose agar. Four representative strains were fluorescent on KMB and gram-negative based on lysis by KOH. Strains were positive for levan formation, negative for oxidase and arginine dihydrolase, and did not cause soft rot on potato slices but induced a hypersensitive response in tobacco (Nicotiana tabacum L. cv. Samsun); strains thus belonged to Lelliot's LOPAT group 1, P. syringae (3). All four strains had identical DNA fragment-banding patterns generated by repetitive extragenic palindromic sequence (rep)-PCR using the BOXA1R primer (4). The pattern generated was different than all P. syringae pathovars in genomospecies 1 including P. syringae pv. syringae. According to multilocus sequence analysis conducted by previously described methods, the strains are most closely related to P. syringae pv. aceris and P. syringae pv. solidagae in genomospecies 1 (1). Potted raspberry plants were used to test four strains for pathogenicity. Inoculum was prepared by growing the bacteria on SPA for 48 h and suspending the bacteria in sterile distilled water (SDW) for a final concentration of approximately 10⁷ CFU/ml. Suspensions were sprayed until runoff onto three replicate plants per strain. Control plants were sprayed with SDW until runoff. Plants were enclosed in plastic bags for 24 h and then maintained in a greenhouse (23 to 25°C). After 7 to 8 days, water soaked lesions developed on all inoculated plants; lesions later turned dark brown and appeared similar to symptoms observed in the field. Plants treated with water developed no symptoms. Bacteria re-isolated onto KMB from symptomatic tissues were fluorescent and appeared identical to the bacteria used to inoculate the plants; two selected re-isolated strains were identical to the original strains according to rep-PCR, fluorescence, and LOPAT reactions. The experiment was repeated and disease development and recovery of fluorescent strains on KMB was identical to the first experiment. To our knowledge, this is the first report of Pseudomonas blight of raspberry, caused by P. syringae, in California. Affected plants initially were stunted in growth but later in the summer exhibited no lasting effects from the disease. Pseudomonas blight has been reported in the Pacific Northwest region of the United States, the British Columbia region of Canada, and Serbia (2). References: (1) C. T. Bull et al. Phytopathology 101:847, 2011. (2) Z. Ivanovic et al. Eur. J. Plant Pathol. 134:191, 2012. (3) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966. (4) A. S. A. Marques, et al. Genet. Mol. Biol. 31:106. 2008.

First Report of Bacterial Leaf Blight on Mustard Greens (Brassica juncea) Caused by Pseudomonas cannabina pv. alisalensis in Mississippi

In 2010, a brassica leafy greens grower in Sunflower County, MS, observed scattered outbreaks of a leaf blight on mustard greens (Brassica juncea) in a 180-ha field. A severe outbreak of leaf blight occurred on mustard greens and turnip greens (B. rapa) in the same field in 2011 with more than 80 ha affected. The affected field, established in 2010, had no prior history of being cropped to brassica leafy greens. Symptoms appeared on the 6-week-old transplants as brown to tan necrotic spots with faint chlorotic borders and associated water-soaking. Lesions varied from 4 mm to 3 cm in diameter and often coalesced to cover >90% of older leaves. Whole plants of the mustard greens cv. Florida Broadleaf were collected in 2011 from the symptomatic field. Leaves were surface-disinfested with 0.5% NaOCl for 5 min, rinsed twice in sterilized distilled water [(sd)H₂O], macerated in sdH₂O, then streaked onto nutrient agar (NA), pseudomonas agar F (PAF), and potato dextrose agar (PDA). Little or no bacterial growth was observed on PDA, while on NA and PAF the majority of bacterial growth appeared to be a single colony type. All strains collected (25 total, one per plant) were gram-negative and fluoresced blue-green under UV light after 48 h at 28°C on PAF. All 25 strains were identified as belonging to Pseudomonas group 1a using Lelliot's determinative assay (2). Ten of the 25 strains were tested for pathogenicity on Florida Broadleaf, and turnip greens cv. Alamo. Bacteria were grown on PAF for 48 h, and a bacterial suspension was prepared and adjusted to an optical density of 0.1 at 600 nm. Three-week-old plants (three plants per cultivar) were sprayed with the appropriate bacterial suspension to runoff, placed at 100% relative humidity for 48 h, and then put in a growth chamber at 28°C with a 16-h diurnal light cycle for 14 days. Additionally, three plants each of Florida Broadleaf and Alamo were either sprayed with H₂O or inoculated with Pseudomonas cannabina pv. alisalensis (Pca) pathotype strain BS91 (1). All 10 strains, as well as the Pca pathotype strain, were pathogenic on both cultivars and caused symptoms similar to those observed in the field. Symptoms were not observed on H₂O-sprayed plants. Comparative rep-PCR analysis using the BOXA1R primer showed the 10 strains had identical DNA-banding profiles and were identical to that of Pca BS91 (5). Five strains tested using a Pca-specific, 'light-tagged' reporter bacteriophage gave a strong positive reaction, while a negative control strain, P. syringae pv. maculicola, gave no signal (3). From these tests, the isolated bacteria were determined to be Pca. Bacteria re-isolated on PAF from the inoculated Florida Broadleaf plants had identical rep-PCR profiles with those of the strains used for inoculations. Over the past 10 years, Pca has been found in numerous states in the United States, as well as in Europe, Australia, and Japan (4). As brassica leafy greens production expands to new fields and new states, leaf blight caused by Pca appears to become a problem rapidly. Since resistant cultivars and highly effective bactericides are lacking, growers are extremely concerned about the rapid spread of this disease into existing and new brassica leafy greens regions. References: (1) N. A. Cintas et al. Plant Dis. 86:992, 2002. (2) R. Lelliott. J. Appl. Bacteriol. 29:470, 1066. (3) D. Schofield et al. Appl. Environ. Microbiol. 78:3592, 2012. (4) F. Takahashi et al. J. Gen. Plant Pathol. 79:260, 2013. (5) J. Versalovic et al. Methods Mol. Cell Biol 5:25, 1994.

Comparative genomics of multiple strains of Pseudomonas cannabina pv. alisalensis, a potential model pathogen of both monocots and dicots

Comparative genomics of closely related pathogens that differ in host range can provide insights into mechanisms of host-pathogen interactions and host adaptation. Furthermore, sequencing of multiple strains with the same host range reveals information concerning pathogen diversity and the molecular basis of virulence. Here we present a comparative analysis of draft genome sequences for four strains of Pseudomonas cannabina pathovar alisalensis (Pcal), which is pathogenic on a range of monocotyledonous and dicotyledonous plants. These draft genome sequences provide a foundation for understanding host range evolution across the monocot-dicot divide. Like other phytopathogenic pseudomonads, Pcal strains harboured a hrp/hrc gene cluster that codes for a type III secretion system. Phylogenetic analysis based on the hrp/hrc cluster genes/proteins, suggests localized recombination and functional divergence within the hrp/hrc cluster. Despite significant conservation of overall genetic content across Pcal genomes, comparison of type III effector repertoires reinforced previous molecular data suggesting the existence of two distinct lineages within this pathovar. Furthermore, all Pcal strains analyzed harbored two distinct genomic islands predicted to code for type VI secretion systems (T6SSs). While one of these systems was orthologous to known P. syringae T6SSs, the other more closely resembled a T6SS found within P. aeruginosa. In summary, our study provides a foundation to unravel Pcal adaptation to both monocot and dicot hosts and provides genetic insights into the mechanisms underlying pathogenicity.

"Light-tagged" bacteriophage as a diagnostic tool for the detection of phytopathogens

Detection of the phytopathogen Pseudomonas cannabina pv alisalensis, the causal agent of bacterial blight of crucifers is essential for managing this disease. A phage-based diagnostic assay was developed that detects and identifies P. cannabina pv alisalensis from cultures and diseased plant specimens. A recombinant "light-tagged" reporter phage was generated by integrating the luxAB genes into the P. cannabina pv alisalensis phage PBSPCA1 genome. PBSPCA1::luxAB is viable, stable and detects P. cannabina pv alisalensis within minutes and with high sensitivity by conferring a bioluminescent signal. Detection is dependent on cell viability since cells treated with a bactericidal disinfectant are unable to elicit a signal. Importantly, the reporter phage detects P. cannabina pv alisalensis from diseased plant specimens indicating the potential of the diagnostic for disease identification. The reporter phage displays promise for the rapid and specific diagnostic detection of cultivated isolates, and infected plant specimens.

Bacterial Leaf Spot of Radicchio (Cichorium intybus) is caused by Xanthomonas hortorum

Radicchio (Cichorium intybus) is ranked 22 among crops in Monterey County, California, with a farm gate value of $19,531,000 (3). Beginning in 2002, a leaf spot disease of radicchio was observed in Monterey County. The disease began as small lesions and in some cases coalesced into larger, irregular spots. Lesions were maroon to dark brown; in some cases, the margins of brown lesions became dark maroon with aging. Each leaf spot was observable from both adaxial and abaxial leaf surfaces. Symptoms primarily occurred on the outer foliage of the heads, though on occasion the head cap leaf could develop lesions. Disease incidence in the first year resulted in up to 10% unharvested radicchio because of cap leaf infections or reduced head size if outer wrapper leaves were all removed; outbreaks in subsequent seasons were more limited. Bacteria forming yellow mucoid colonies were isolated from surface disinfested symptomatic tissue that was macerated and streaked onto sucrose peptone agar medium. Bacteria were gram negative, did not fluoresce on King's Medium B, and used esculin as a carbon source but used none of the other 48 carbon sources tested using the API 50 CH test strip. Nine isolates from symptomatic radicchio had the same DNA fragment banding pattern generated by repetitive extragenic palindromic sequence polymerase chain reactions (rep-PCR) using the BOXA1R primer. Amplicons of rpoD, dnaK, fyuA, and gyrB for multilocus sequence typing (MLST) were generated using a modification of the scheme developed by Young et al. (4) and sequenced by a commercial laboratory. Concatenated sequences of the four genes from the radicchio isolates were compared to the sequences available in the Plant Associated and Environmental Microbes Database (1). The genetic distance between the nine isolates from radicchio and pathotypes of Xanthomonas hortorum were 0.03 or less and MLST analysis indicated that radicchio isolates were members of the species X. hortorum (2). To complete Koch's postulates, freshly grown cultures were suspended in phosphate buffer and adjusted to approximately 5 × 10⁸ CFU/ml. The inoculum was sprayed onto the undersides of leaves of 40-day-old radicchio plants (C. intybus cv. Leonardo). Plants were incubated at 100% humidity for 48 h and then moved to a greenhouse. Plants sprayed with buffer served as negative controls. For each of the two experiments conducted, there were three and six single-plant replicates per treatment. The buffer treated plants did not develop symptoms but the plants treated with isolates from radicchio developed leaf spots similar to those observed in the field with symptoms beginning to be visible after 5 days. The bacteria isolated from symptomatic tissue on inoculated plants were identical to the original strains when compared with rep-PCR, thus completing Koch's postulates. Results from the two experiments were similar. To our knowledge, this is the first report of X. hortorum causing a leaf spot disease on radicchio. The disease continues to occur sporadically on radicchio grown in coastal California. References: (1) Almeida et al. Phytopathology 100:208, 2010. (2) Bull et al. Phytopathology 101:847, 2011. (3) Lauritzen, Monterey County Crop Report, 2010; (4) Young et al. Syst. Appl. Microbiol. 31:366, 2008.

First Report of the Crucifer Pathogen Pseudomonas cannabina pv. alisalensis Causing Bacterial Blight on Radish (Raphanus sativus) in Germany

In 2008, a bacterial blight was observed on Raphanus sativus in the Pfalz region in Germany. Disease was sporadic but severe when present within R. sativus fields, which resulted in unmarketable crops. Symptoms consisted of small, angular, water-soaked flecks that often were surrounded by chlorotic haloes. Lesions were visible from adaxial and abaxial leaf surfaces and generally retained chlorotic borders. A gram-negative, bluefluorescing bacterium was isolated from surface-disinfested leaf tissue on King's medium B agar. The radish isolate was levan positive, oxidase negative, and arginine dihydrolase negative. The isolate did not rot potato slices but induced a hypersensitive reaction in tobacco. These reactions corresponded to Lelliot's LOPAT group 1 (2). Repetitive extragenic palindromic sequence (rep)-PCR assays using the BOXA1R primer resulted in different DNA fragment banding patterns between the radish isolate and the pathotype strain of Pseudomonas syringae pv. maculicola (CFBP 1657), but identical DNA fragment banding patterns between the radish isolate and the pathotype strain of P. cannabina pv. alisalensis (CFBP 6866). Unlike P. syringae pv. maculicola, P. cannabina pv. alisalensis and the radish isolate were lysed by bacteriophage PBS1 (1). Pathogenicity was evaluated on two hosts, radish (R. sativus cv. Comet) and broccoli raab (Brassica rapa cv. Sorrento). In each of two independent experiments, 3-week-old radish and broccoli raab plants were inoculated with either the radish isolate, P. cannabina pv. alisalensis, or P. syringae pv. maculicola. Inoculum was prepared by growing the bacteria on nutrient agar for 48 h at 27°C, suspending the bacteria in 0.01 M phosphate buffer (pH 7.0), and adjusting each suspension to 0.6 OD at 600 nm (approximately 1 × 10⁸ CFU/ml). All plants were inoculated by spraying until runoff, incubated in a humidity chamber for 48 h, then placed in a greenhouse at 20 to 25°C for symptom development. Plants inoculated with P. cannabina pv. alisalensis or sprayed with buffer served as positive and negative control treatments, respectively. Seven to ten days postinoculation, the development of symptoms similar to those originally observed in the field were observed on plants inoculated with the radish isolate. In addition, symptoms on radish and broccoli raab plants caused by the radish isolate were similar to symptoms caused by P. cannabina pv. alisalensis in contrast to the lack of symptoms on plants inoculated with P. syringae pv. maculicola. Bacteria isolated from symptomatic tissue and surface-disinfested with sodium hypochlorite (0.525%) had identical characteristics to the radish isolate used to inoculate plants and to the P. cannabina pv. alisalensis pathotype for LOPAT reactions, rep-PCR DNA fragment banding pattern analysis, and sensitivity to phage PBS1, thus fulfilling Koch's postulates. To our knowledge, this is the first report of P. cannabina pv. alisalensis isolated from diseased crucifers in Germany. Verification of P. cannabina pv. alisalensis in Germany indicates that German crucifer growers should differentiate between outbreaks caused by P. cannabina pv. alisalensis and P. syringae pv. maculicola and apply appropriate, specific management strategies. References: (1) C. T. Bull et al. Syst. Appl. Microbiol. 33:105, 2010. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

Development of an engineered bioluminescent reporter phage for detection of bacterial blight of crucifers

Bacterial blight, caused by the phytopathogen Pseudomonas cannabina pv. alisalensis, is an emerging disease afflicting important members of the Brassicaceae family. The disease is often misdiagnosed as pepper spot, a much less severe disease caused by the related pathogen Pseudomonas syringae pv. maculicola. We have developed a phage-based diagnostic that can both identify and detect the causative agent of bacterial blight and differentiate the two pathogens. A recombinant "light"-tagged reporter phage was generated by integrating bacterial luxAB genes encoding luciferase into the genome of P. cannabina pv. alisalensis phage PBSPCA1. The PBSPCA1::luxAB reporter phage is viable and stable and retains properties similar to those of the wild-type phage. PBSPCA1::luxAB rapidly and sensitively detects P. cannabina pv. alisalensis by conferring a bioluminescent signal response to cultured cells. Detection is dependent on cell viability. Other bacterial pathogens of Brassica species such as P. syringae pv. maculicola, Pseudomonas marginalis, Pectobacterium carotovorum, Xanthomonas campestris pv. campestris, and X. campestris pv. raphani either do not produce a response or produce significantly attenuated signals with the reporter phage. Importantly, the reporter phage detects P. cannabina pv. alisalensis on diseased plant specimens, indicating its potential for disease diagnosis.

First Report of Bacterial Streak of Fennel (Foeniculum vulgare) in California Caused by Pseudomonas syringae pv. apii

A previously undescribed disease appeared on commercially grown fennel (Foeniculum vulgare) in Salinas (Monterey County), CA in March 2010. Initial symptoms consisted of small, dark brown-to-black lesions on leaves and stems. As disease progressed, lesions expanded in a linear fashion and eventually spread down the stems and into the bulbs. Once the disease reached the fennel bulbs, the plants were unmarketable. Eighteen, gram-negative, blue-fluorescing bacterial isolates were obtained on sucrose peptone agar from individual plants of two outbreaks from different fields in Salinas. The isolates were dome shaped on sucrose-amended media and produced necrotic lesions when injected into tobacco. Isolates were oxidase negative and did not rot potatoes or hydrolyze arginine. These reactions corresponded to Lelliot's group 1, which includes Pseudomonas syringae (2). The fennel isolates were identical to recently characterized isolates of P. syringae pv. apii from parsley grown in coastal California (1) and similar to the pathotype strain of P. syringae pv. apii according to DNA fragment banding patterns of amplicons generated from repetitive extragenic palindromic sequence (rep)-PCR using the BOXA1R primer. The isolates were distinct from the pathotype strain P. syringae pv. coriandricola. Like P. syringae pv. apii, the fennel isolates did not nucleate ice but did hydrolyze gelatine. Six isolates were tested for pathogenicity in each of two independent experiments with a total of six replications per isolate. Healthy, potted fennel plant stems of a proprietary cultivar were pierced once with insect display pins that had been dipped into bacterial colonies grown for 48 h on nutrient agar. Control stems were inoculated with sterile pins. Plants were incubated for 48 h at 100% relative humidity and then held in a greenhouse. After 4 to 6 days, inoculated fennel plants developed symptoms similar to those originally observed in the field. Bacteria isolated from surface-disinfested symptomatic tissue were fluorescent and identical to strains used to inoculate plants as evaluated by rep-PCR, thus fulfilling Koch's postulates. Control plants remained symptomless. To our knowledge, this is the first report of this pathogen causing a disease on fennel; the disease has been named bacterial streak. The disease occurred in three fields in 2010 and incidence was <1% in each case. Similar symptoms were also observed on fennel in the 2011 season in at least two fields. Previously, the host range of P. syringae pv. apii was reported to be restricted to celery. This research expands the natural host range of P. syringae pv. apii; thus, care should be taken in choosing Apiaceae crops for plantings subsequent to the occurrence of this pathogen. References: (1) C. T. Bull et al. Phytopathology 101:847, 2011. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

First Report of Bacterial Blight of Crucifers Caused by Pseudomonas cannabina pv. alisalensis in Australia

In 1978 and 1979, Pseudomonas syringae pv. maculicola strains DAR 33362, DAR 33363, and DAR 33406 were isolated from diseased Brassica hirta, B. nigra, and B. napus var. napus, respectively, in Wagga Wagga and Armatree, NSW, Australia (2). Peters et al. (2) demonstrated that these strains were similar to P. syringae pv. maculicola ICMP 4326 (CFBP 1637), which was recently transferred to Pseudomonas cannabina pv. alisalensis (1). We evaluated these Australian strains to determine if they might also be P. cannabina pv. alisalensis. Amplification of DNA using the BOXA1R primer and PCR resulted in identical DNA fragment banding patterns for Australian strains DAR 33362 and DAR 33363 and P. cannabina pv. alisalensis ICMP 4326 and CFBP 6875. The third Australian strain, DAR 33406, was 90% similar to P. cannabina pv. alisalensis; in contrast, it was only 77% similar to P. syringae pv. maculicola. All strains of P. cannabina pv. alisalensis, including the pathotype strain (CFBP 6866) and all three Australian strains, were lysed by bacteriophage PBS1, which is specific for P. cannabina pv. alisalensis strains (1). To complete Koch's postulates, pathogenicity was evaluated on B. hirta, B. nigra, and B. napus var. napus. In two independent experiments, two plants of each species were inoculated with each Australian strain or a phosphate buffer control treatment. In separate experiments, pathogenicity was evaluated on the differential hosts radish (Raphanus sativus cv. Comet) and broccoli raab (Brassica rapa cv. Sorrento), and plants inoculated with the pathotypes of P. cannabina pv. alisalensis and P. syringae pv. maculicola served as additional control treatments. Inoculum was prepared by growing the bacteria on nutrient agar for 48 h (27°C), suspending the bacteria in 0.01 M phosphate buffer (pH 7.0), and adjusting each suspension to 0.6 OD at 600 nm (approximately 10⁸ CFU/ml). Treatments were applied by spraying until runoff. DAR 33362, DAR 33363, and DAR 33406 caused typical bacterial blight symptoms on B. hirta, B. nigra, and B. napus var. napus. Infected leaves became yellow, followed by the development of small (<2 mm in diameter), angular, water-soaked, and eventually, shot-holed spots. Bacteria isolated from symptomatic tissue following surface disinfestation of tissue with sodium hypochlorite (0.525%) had identical characteristics (rep-PCR DNA fragment banding patterns and phage sensitivity) to the strains used to inoculate the plants. Additionally, DAR 33362, DAR 33363, and DAR 33406, as well as P. cannabina pv. alisalensis, caused symptoms on radish and broccoli raab while P. syringae pv. maculicola and the buffer control did not. These data support the transfer of the Australian crucifer strains, originally identified as P. syringae pv. maculicola, to P. cannabina pv. alisalensis. To our knowledge, this is the first report of a bacterial disease of crucifers caused by P. cannabina pv. alisalensis in Australia. Differentiation of these pathogens will inform crop rotation strategies for disease management. References: (1) C. T. Bull et al. Syst. Appl. Microbiol. 33:105, 2010. (2) B. J. Peters et al. Plant Pathol. 53:3, 2004.

Multilocus sequence typing of Pseudomonas syringae sensu lato confirms previously described genomospecies and permits rapid identification of P. syringae pv. coriandricola and P. syringae pv. apii causing bacterial leaf spot on parsley

Since 2002, severe leaf spotting on parsley (Petroselinum crispum) has occurred in Monterey County, CA. Either of two different pathovars of Pseudomonas syringae sensu lato were isolated from diseased leaves from eight distinct outbreaks and once from the same outbreak. Fragment analysis of DNA amplified between repetitive sequence polymerase chain reaction; 16S rDNA sequence analysis; and biochemical, physiological, and host range tests identified the pathogens as Pseudomonas syringae pv. apii and P. syringae pv. coriandricola. Koch's postulates were completed for the isolates from parsley, and host range tests with parsley isolates and pathotype strains demonstrated that P. syringae pv. apii and P. syringae pv. coriandricola cause leaf spot diseases on parsley, celery, and coriander or cilantro. In a multilocus sequence typing (MLST) approach, four housekeeping gene fragments were sequenced from 10 strains isolated from parsley and 56 pathotype strains of P. syringae. Allele sequences were uploaded to the Plant-Associated Microbes Database and a phylogenetic tree was built based on concatenated sequences. Tree topology directly corresponded to P. syringae genomospecies and P. syringae pv. apii was allocated appropriately to genomospecies 3. This is the first demonstration that MLST can accurately allocate new pathogens directly to P. syringae sensu lato genomospecies. According to MLST, P. syringae pv. coriandricola is a member of genomospecies 9, P. cannabina. In a blind test, both P. syringae pv. coriandricola and P. syringae pv. apii isolates from parsley were correctly identified to pathovar. In both cases, MLST described diversity within each pathovar that was previously unknown.

First Report of Bacterial Blight of Cabbage (Brassica oleracea var. capitata) Caused by Pseudomonas cannabina pv. alisalensis in California

In 2008, field-grown cabbage (Brassica oleracea var. capitata L., cv. Grenader) from Monterey County, California showed symptoms on the wrapper leaves of immature plants that had formed heads. Initial symptoms consisted of small, brown, water-soaked flecks surrounded by chlorotic haloes. These flecks later coalesced into large, irregularly shaped, brown-black, necrotic lesions with chlorotic haloes visible on both adaxial and abaxial surfaces of the leaf. This disease resulted in lower quality and reduced marketability of the cabbage. Five gram-negative, blue-green fluorescing bacteria were isolated from separate lesions on different plants on King's medium B agar. The isolates were positive for levan formation and negative for oxidase and arginine dihydrolase. The isolates did not cause soft rot on potato slices but did induce a hypersensitive reaction in tobacco (Nicotiana tabacum L. cv. Samsun). These data indicated that the bacteria belonged to Lelliot's LOPAT group 1 (2). Repetitive extragenic palindromic sequence (rep)-PCR using the BOXA1R primer resulted in identical DNA fragment banding patterns for the cabbage isolates and the pathotype of Pseudomonas cannabina pv. alisalensis (formerly P. syringae pv. alisalensis). Additionally, both P. cannabina pv. alisalensis and the five cabbage isolates were sensitive to bacteriophage PBS1 while the pathotype strain of P. syringae pv. maculicola was not (1). Pathogenicity of the five cabbage isolates was evaluated in two independent experiments. Inoculum was prepared by growing the bacteria on nutrient agar for 48 h (27°C), suspending the bacteria in 0.01 M phosphate buffer (pH 7.0), adjusting each suspension to 0.6 OD at 600 nm (approximately 10⁸ CFU/ml), and adding three to five drops of Tween 20. In each experiment, two cabbage, broccoli raab (Brassica rapa subsp. rapa cv. Sorrento), and oat (Avena sativa cv. Montezuma) plants were inoculated for each isolate by spraying until runoff. Positive control plants were inoculated with the pathotype strain of P. cannabina pv. alisalensis and negative control plants were treated with sterile 0.01 M phosphate buffer. The plants were placed in a mist chamber for 48 to 72 h and then in a greenhouse (20 to 25°C). After 7 to 10 days, foliar symptoms similar to symptoms observed on the original diseased cabbage plants developed on all inoculated plants including the positive control plants inoculated with P. cannabina pv. alisalensis. Additionally severe symptoms on broccoli raab and minor symptoms on oats developed on plants inoculated with cabbage strains or P. cannabina pv. alisalensis. For each experiment, bacteria reisolated from symptomatic tissue were identical to the bacteria used to inoculate the plants and to P. cannabina pv. alsialensis for rep-PCR DNA fragment banding pattern and sensitivity to phage PBS1. There were no symptoms on any of the cabbage and oat negative controls. Additionally, there were no symptoms on any broccoli raab negative controls in the first experiment; however, in the second experiment, a small (<1 mm) lesion was detected on one leaf of one plant. To our knowledge, this is the first report of P. cannabina pv. alisalensis causing bacterial blight of cabbage in California. This disease may have significant impact because of the large acreage of cabbage grown in California (approximately 5,666 ha annually). References: (1) C. T. Bull et al. Syst. Appl. Microbiol. 33:105, 2010. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

First Report of Bacterial Blight of Brussels sprouts (Brassica oleracea var. gemmifera) Caused by Pseudomonas cannabina pv. alisalensis in California

Greenhouse-grown Brussels sprouts (Brassica oleracea L. var. gemmifera) transplants from Monterey County, California showed symptoms in 2006 of a previously undescribed disease. Initial symptoms consisted of small (1 to 2 mm in diameter), angular, water-soaked flecks, some of which were surrounded by chlorotic haloes. These flecks coalesced into large, irregularly shaped, gray brown lesions as large as 10 mm. Lesions were visible from both adaxial and abaxial leaf surfaces and generally retained chlorotic borders. This disease resulted in decreased quality and reduced marketability of the transplants. Gram-negative, blue-green fluorescing bacteria were consistently isolated from lesions on King's medium B agar. Ten isolates were selected and used in further studies. Isolates were levan positive, oxidase negative, and arginine dihydrolase negative. Isolates did not rot potato slices but induced a hypersensitive reaction in tobacco (Nicotiana tabacum L. cv. Samsun). These data indicated that the bacteria belonged to Lelliot's LOPAT group 1 (2). Repetitive extragenic palindromic sequence (REP)-PCR using the BOXA1R primer resulted in identical DNA fragment banding patterns for the Brussels sprouts isolates and the pathotype of Pseudomonas cannabina pv. alisalensis (formerly P. syringae pv. alisalensis). Like P. cannabina pv. alisalensis, the isolates from Brussels sprouts were sensitive to bacteriophage PBS1 (1). All 10 isolates were used in two independent pathogenicity experiments. Inoculum for pathogenicity studies was prepared by growing the bacteria on nutrient agar for 48 h (27°C), suspending the bacteria in 0.01 M phosphate buffer (pH 7.0), and adjusting each suspension to 0.6 OD at 600 nm (approximately 10⁸ CFU/ml). In each experiment, six Brussels sprouts plants were inoculated for each isolate by spraying until runoff or by swabbing a suspension of the appropriate bacterial isolate to which Carborundum had been added. Additionally, four Brussels sprouts isolates were used to spray inoculate six broccoli raab (Brassica rapa subsp. rapa) plants. Positive control plants were inoculated with the pathotype of P. cannabina pv. alisalensis, and the negative control plants were inoculated with sterile buffer or sterile buffer with Carborundum. Inoculated plants were placed in a mist chamber for 48 h and then in a greenhouse (20 to 25°C). After 5 to 7 days, foliar symptoms similar to symptoms observed on the original diseased Brussels sprouts plants developed on all inoculated plants, including the positive control plants inoculated with P. cannabina pv. alisalensis. Negative control plants remained symptomless. In each experiment, bacteria reisolated from symptomatic tissue were identical to the bacteria used to inoculate the plants and to P. cannabina pv. alisalensis for LOPAT reactions, REP-PCR DNA fragment banding pattern, and sensitivity to phage PBS1. To our knowledge, this is the first report of P. cannabina pv. alisalensis causing bacterial blight of Brussels sprouts. References: (1) C. T. Bull et al. Syst. Appl. Microbiol. 33:105, 2010. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

PAMDB, a multilocus sequence typing and analysis database and website for plant-associated microbes

Although there are adequate DNA sequence differences among plant-associated and plant-pathogenic bacteria to facilitate molecular approaches for their identification, identification at a taxonomic level that is predictive of their phenotype is a challenge. The problem is the absence of a taxonomy that describes genetic variation at a biologically relevant resolution and of a database containing reference strains for comparison. Moreover, molecular evolution, population genetics, ecology, and epidemiology of many plant-pathogenic and plant-associated bacteria are still poorly understood. To address these challenges, a database with web interface was specifically designed for plant-associated and plant-pathogenic microorganisms. The Plant-Associated Microbes Database (PAMDB) comprises, thus far, data from multilocus sequence typing and analysis (MLST/MLSA) studies of Acidovorax citrulli, Pseudomonas syringae, Ralstonia solanacearum, and Xanthomonas spp. Using data deposited in PAMDB, a robust phylogeny of Xanthomonas axonopodis and related bacteria has been inferred, and the diversity existing in the Xanthomonas genus and in described Xanthomonas spp. has been compared with the diversity in P. syringae and R. solanacearum. Moreover, we show how PAMDB makes it easy to distinguish between different pathogens that cause almost identical diseases. The scalable design of PAMDB will make it easy to add more plant pathogens in the future.

First Report of Blossom Blight of Strawberry (Fragaria × ananassa) Caused by Pseudomonas marginalis

In 2003, a new disease was observed on commercial strawberries (Fragaria × ananassa Duch.) grown in multiple fields in Watsonville, CA. Initial symptoms consisted of brown lesions on the undersides of the sepals of strawberry flowers. The lesions coalesced and spread to upper sepal surfaces and anther bases. No leaf symptoms were observed. Fields affected with this disease appeared to have a greater number of deformed fruit, though incidence data were not collected. A gram-negative, blue-green fluorescent pseudomonad was isolated from lesions on King's medium B agar from both sepals and anthers from 23 of 24 samples from three different fields. All isolates were levan, oxidase, and arginine dihydrolase positive. The strains did rot potato slices but did not induce a hypersensitive reaction in tobacco (Nicotiana tabacum L. cv. Sansun), indicating that the bacteria belonged to Lelliot's LOPAT group IVa, P. marginalis (3). Isolates from strawberry were compared with pathotype strains of Pseudomonas marginalis pv. marginalis, P. marginalis pv. alfalfae, and P. marginalis pv. pastinaceae. The 16S rDNA sequence of type strain of P. marginalis (Z76663) was 97 to 99% similar to the four strawberry isolates sequenced (GQ845121). Identity was further supported by analysis of fatty acid methyl esters (MIS-TSBA version 4.10; MIDI, Inc., Newark, DE). Polymerase chain reaction using BOX-A1R primers (repetitive sequence-based (rep)-PCR [1]) resulted in DNA fragment banding patterns that were identical among strawberry isolates. These banding patterns were different from the three distinct patterns of the P. marginalis pathotypes. Pathogenicity on strawberry (cv. Albion) was confirmed in three experiments using four strawberry isolates originally isolated from plants from three different fields and the P. marginalis pathotype strains. Inoculum was produced by growing bacteria in nutrient broth shake cultures for 48 h (24°C) and washing and suspending the cultures in 0.01 M phosphate buffer (pH 7.0). Three to five attached strawberry flowers on separate plants were dipped in the bacterial suspensions (10⁶ CFU/ml) or sterile buffer for 1 min. To maintain high humidity, flower buds were enclosed in plastic bags for 36 to 48 h and then incubated in the greenhouse (24 to 26°C). After 7 days, approximately half of the flowers inoculated with the strawberry isolates had symptoms on sepals that were identical to symptoms seen in the field. Additionally, reisolates obtained from the symptomatic, inoculated flowers were identical to those used to inoculate the plants as confirmed by LOPAT reactions and rep-PCR, thus completing Koch's postulates. Flowers dipped in phosphate buffer or the P. marginalis pathotype strains did not develop symptoms and no bacteria were reisolated. To our knowledge, this is the first report of blossom blight of strawberry caused by P. marginalis and the first report of P. marginalis on strawberry in California. P. marginalis causes leaf bud rot of strawberry in Japan (2). Further research is needed to determine if the strawberry isolates represent a new or previously described pathovar of P. marginalis. References: (1) N. A. Cintas et al. Plant Dis. 86:992, 2002. (2) T. Kijima et al. Bull. Tochigi. Agric. Exp. Stn. 36:59, 1989. (3) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

First Report of Bacterial Blight on Conventionally and Organically Grown Arugula in Nevada Caused by Pseudomonas syringae pv. alisalensis

In 2007, leaf spots were observed on arugula (Eruca vesicaria subsp. sativa cv. My Way) grown under sprinkler irrigation for fresh market in conventional and organic production fields located above 1,200 m (4,000 feet) in Nevada (NV). Approximately 30% of each planting was affected. Initially, symptoms consisted of small (<2 mm in diameter), angular, water-soaked spots visible from both sides of the leaf, some of which developed a shot-hole appearance. The spots enlarged and coalesced, remaining angular. Lesions ranged from black to tan, occasionally developing a chlorotic or purple margin. Some lesions resembled symptoms of downy mildew on arugula, but microscopic examination revealed no sporangiophores associated with the lesions. Bacterial ooze was observed when sections of symptomatic leaves were examined microscopically. Blue-green fluorescent pseudomonads were isolated from lesions on King's medium B agar from three arugula plantings. Twelve strains (at least three from each planting) were evaluated along with known strains of Pseudomonas syringae pv. alisalensis and P. syringae pv. maculicola in all assays. Bacterial strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction on tobacco (Nicotiana tabacum L. cv. Sansun) indicating that the bacteria belonged to Lelliot's LOPAT group 1 (2). This was confirmed by analysis of fatty acid methyl esters (MIS-TSBA version 4.10; MIDI, Inc., Newark, DE), which indicated that the strains were highly similar (similarity >0.80) to P. syringae. Amplification of DNA between repetitive bacterial sequences (rep-PCR) using the BOXA1R primer resulted in identical banding patterns for the NV arugula strains and P. syringae pv. alisalensis from arugula in California (1). Koch's postulates were completed by confirming pathogenicity of the isolated strains on the arugula cvs. Italian and Astro. Strains were grown on nutrient agar for 48 h at 27°C, adjusted to 10⁸ CFU/ml in sterile 0.01 M phosphate buffer (pH 7.0), and spray inoculated until runoff onto 2- to 3-week-old plants. Control plants were similarly sprayed with sterile phosphate buffer. Plants were held for 2 days in a mist chamber and 7 days on a greenhouse bench (24 to 26°C). Angular lesions similar to symptoms observed on the original plants developed on leaves of all inoculated arugula plants. In addition, some plants developed blackening of the smaller veins accompanied by chlorosis of the surrounding interveinal tissue in 10- to 20-mm diameter areas of the leaves. Small black lesions (as much as 10 mm long) were also observed on the petioles. Bacterial strains reisolated from the symptomatic tissue were identical to P. syringae pv. alisalensis by rep-PCR. Control plants remained symptomless. Similar inoculation and incubation methods confirmed that the host range of the NV arugula isolates was identical to that of known strains of P. syringae pv. alisalensis. The arugula and P. syringae pv. alisalensis isolates caused leaf spots on broccoli raab (Brassica rapa subsp. rapa cv. Sorento) and oats (Avena sativa cv. Montezuma). Pathogenicity tests were repeated. This confirms that the leaf spot observed on conventionally and organically grown arugula in NV was caused by P. syringae pv. alisalensis. To our knowledge, this is the first report of this disease on arugula in NV. References: (1) C. T. Bull et al. Plant Dis. 88:1384, 2004. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

First Report of Bacterial Blight of Rutabaga (Brassica napus var. napobrassica) Caused by Pseudomonas syringae pv. alisalensis in California

In 2005, commercial, organically grown rutabaga (Brassica napus var. napobrassica) in San Benito County, CA showed symptoms of a previously undescribed disease on approximately 30% of the plants. Initial symptoms consisted of small (1 to 2 mm in diameter), angular, water-soaked flecks that often were surrounded by chlorotic haloes. These flecks enlarged and coalesced into large, irregularly shaped, gray brown lesions that could be as long as 10 mm. Lesions were visible from both adaxial and abaxial leaf surfaces and generally retained the chlorotic borders. A blue-green fluorescing pseudomonad was consistently isolated from lesions on King's medium B. Eight isolates were characterized and were levan positive, oxidase negative, and arginine dihydrolase negative. Isolates did not rot potato slices but induced a hypersensitive reaction in tobacco (Nicotiana tabacum cv. Samsun). These data indicated that the bacteria belonged to Lelliot's LOPAT group 1 (2). This was confirmed with data from fatty acid methyl ester analysis (MIS-TSBA version 4.10; MIDI, Inc., Newark, DE) that showed that the isolates were highly similar (similarity = 0.922 or greater) to Pseudomonas syringae. Amplification of repetitive bacterial sequences (rep-PCR) using the BOXA1R primer and the polymerase chain reaction resulted in identical banding patterns for the rutabaga isolates and the P. syringae pv. alisalensis pathotype strain. Pathogenicity was demonstrated by growing inocula of six isolates in nutrient broth shake cultures for 48 h (24°C), adjusting the bacterial suspension to 10⁶ CFU/ml, and misting the resulting suspensions onto rutabaga (cv. American Purple Top). Plants were enclosed in plastic bags for 24 h and then incubated in a greenhouse (24 to 26°C). Control plants were misted with sterile water and treated the same way. After 5 to 7 days, foliar symptoms similar to symptoms seen in the field developed on all inoculated plants, and reisolated bacteria were characterized and found to be P. syringae pv. alisalensis. Control plants remained symptomless. The results of two sets of pathogenicity tests were the same. To our knowledge, this is the first report of commercially grown rutabaga as a host of P. syringae pv. alisalensis and the first report of a B. napus host of this pathogen. This bacterial pathogen has previously been reported on commercial plantings of arugula (Eruca sativa), broccoli (Brassica oleracea var. botrytis), and broccoli raab (Brassica rapa var. rapa) in California and under experimental conditions it causes disease on additional hosts, including members of the Poaceae (1). References: (1) N. A. Cintas et al. Plant Dis. 86:992, 2002. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

First Report of Bacterial Blight of Romanesco Cauliflower (Brassica oleracea var. botrytis) Caused by Pseudomonas syringae pv. alisalensis in California

In 2005, a new disease was detected on commercial, organically grown romanesco (green) cauliflower (Brassica oleracea var. botrytis) grown in San Benito County, California. Initial symptoms consisted of small (1 to 2 mm in diameter), angular, water-soaked flecks. These flecks developed into tan-to-gray, angular lesions measuring as much as 5 mm in diameter. Lesions were usually surrounded by chlorotic borders. Coalescing lesions caused the leaf to turn papery in texture and have a blighted appearance. A blue-green fluorescing pseudomonad was consistently isolated from lesions on King's medium B. Strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction in tobacco (Nicotiana tabacum cv. Samsun). These data indicated that the bacteria belonged to Lelliot's LOPAT group 1 (2). This was confirmed with data from fatty acid methyl ester analysis (MIS-TSBA version 4.10, MIDI, Inc., Newark, DE), which showed that the strains were highly similar (similarity = 0.921 or greater) to Pseudomonas syringae. Amplification of repetitive bacterial sequences (rep-PCR) using the BOXA1R primer and the polymerase chain reaction resulted in identical banding patterns for the romanesco strains and the P. syringae pv. alisalensis pathotype strain. Pathogenicity was demonstrated by growing inoculum of six strains in nutrient broth shake cultures for 48 h (24°C), adjusting the bacterial suspension to 10⁶ CFU/ml, and spraying the resulting suspension onto green cauliflower (cv. Romanesco Precoce). Plants were enclosed in plastic bags for 24 h and then incubated in a greenhouse (24 to 26°C). Control plants were misted with sterile water and treated the same way. After 5 days, foliar symptoms identical to symptoms seen in the field developed on all inoculated plants, and reisolated strains were characterized and found to be identical to P. syringae pv. alisalensis by the tests described above. Control plants remained symptomless. The results of two sets of pathogenicity tests were the same. To our knowledge, this is the first report of commercially grown romanesco green cauliflower as a host of P. syringae pv. alisalensis. The infested field had approximately 30% of the plants affected, with perhaps 10% sustaining some crop loss. This bacterial pathogen has previously been reported on commercial plantings of arugula (Eruca sativa), broccoli (Brassica oleracea var. botrytis), and broccoli raab (Brassica rapa var. rapa) and under experimental (greenhouse) conditions causes disease on additional hosts, including members of the Poaceae (1). References: (1) N. A. Cintas et al. Plant Dis. 86:992, 2002. (2) R. A. Lelliott. J. Appl. Bacteriol. 29:470, 1966.

Holdover Inoculum of Pseudomonas syringae pv. alisalensis from Broccoli Raab Causes Disease in Subsequent Plantings

Uniform plots of broccoli raab (Brassica rapa subsp. rapa) seedlings were inoculated with a rifampicin-resistant strain of Pseudomonas syringae pv. alisalensis, the causal agent of bacterial blight on crucifers, resulting in 100% disease incidence in mature plants. Diseased plants were incorporated into the soil at maturity and smaller replicated plots were replanted at various times after incorporation. Rifampicin-resistant fluorescent pseudomonads with rep-PCR profiles identical to P. syringae pv. alisalensis were isolated from lesions on plants grown in soil into which the first diseased crop was incorporated. Disease incidence declined in mature plants as the length of time between incorporation of the first planting and seeding of the replanted plots increased. Bacterial population levels in soil decreased over time and bacteria were no longer detectable 3 weeks after incorporation of the diseased crop. In laboratory tests, population levels of P. syringae pv. alisalensis decreased in untreated soil but not in autoclaved soil. Greenhouse studies demonstrated a direct correlation between population levels of P. syringae pv. alisalensis applied to soil and disease incidence in seedlings. However, the decline in bacterial populations in field soils did not wholly account for the decline in disease incidence with subsequent plantings.

First Report of Bacterial Leaf Spot of Italian Dandelion (Cichorium intybus) Caused by a Pseudomonas syringae Pathovar in California

Italian dandelion (Cichorium intybus) is a leafy, nonhead forming chicory plant that is eaten as a fresh vegetable in salads. During the late summer (August through October) of 2002, in the Salinas Valley (Monterey County) in California, a previously unreported disease was found in commercial Italian dandelion fields. Early symptoms were angular, vein delimited, dark, water-soaked leaf spots that measured 2 to 7 mm in diameter. As disease developed, spots retained angular edges but exhibited various irregular shapes. Spots commonly formed along the edges of the leaves; in some cases these spots developed into lesions that measured between 10 and 30 mm long. Spots were visible from adaxial and abaxial sides and were dull black in color. A cream-colored pseudomonad was consistently isolated from leaf spots that were macerated and streaked onto sucrose peptone agar. Fungi were not recovered from any of the spots. Recovered strains were blue-green fluorescent when streaked onto King's medium B agar. Bacterial strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction on tobacco (Nicotiana tabacum cv. Turk). These data indicated that the bacteria belonged to LOPAT group 1 of Pseudomonas syringae (1). Pathogenicity of six strains was tested by growing inoculum in nutrient broth shake cultures for 48 h, diluting to 10⁶ CFU/ml, and spraying onto 12 6-week-old plants of Italian dandelion cv. Catalogna Special. Untreated control plants were sprayed with sterile nutrient broth. After 10 to 12 days in a greenhouse (24 to 26°C), leaf spots similar to those observed in the field developed on all inoculated plants. Strains were reisolated from the spots and identified as P. syringae. Control plants remained symptomless. These inoculation experiments were done twice and the results were the same. Amplification of repetitive bacterial sequences (repetitive sequence-based polymerase chain reaction [rep-PCR]) demonstrated that all Italian dandelion strains had the same rep-PCR fingerprint, which differed from fingerprints of P. syringae pv. tagetis and P. syringae pv. tabaci. Additionally, toxin specific primers did not amplify tagetitoxin or tabtoxin biosynthesis genes from Italian dandelion strains. To our knowledge, this is the first report of bacterial leaf spot of commercially grown Italian dandelion in California caused by a P. syringae pathovar. Because fields were irrigated with overhead sprinklers, the disease was severe in several fields and as much as 30% of those plantings were not harvested. Reference: (1) R. A. Lelliott et al. J. Appl. Bacteriol. 29:470, 1966.

Mutations affecting predation ability of the soil bacterium Myxococcus xanthus

Myxococcus xanthus genetic mutants with characterized phenotypes were analysed for the ability to prey on susceptible bacteria. Quantification of predatory ability was scored by a newly developed method under conditions in which prey bacteria provided the only source of nutrients. These results were corroborated by data derived using a previously published protocol that measures predation in the presence of limited external nutrients. First, early developmental regulatory mutants were examined, because their likely functions in assessing the local nutrient status were predicted to be also important for predation. The results showed that predation efficiency is reduced by 64-80 % for mutants of three A-signalling components, AsgA, AsgC and AsgE, but not for AsgB. This suggests that an Asg regulon function that is separate from A-signal production is needed for predation. Besides the Asg components, mutations in the early developmental genes sdeK and csgA were also consistently observed to reduce predatory efficacy by 36 and 33 %, respectively. In contrast, later developmental components, such as DevRS, 4406 and PhoP4, did not appear to play significant roles in predation. The predatory abilities of mutants defective for motility were also tested. The data showed that adventurous, but not social, motility is required for predation in the assay. Also, mutants for components in the chemotaxis-like Frz system were found to be reduced in predation efficiency by between 62 and 85 %. In sum, it was demonstrated here that defects in development and development-related processes affect the ability of M. xanthus to prey on other bacteria.