Ophiostoma Polonicum is a Species of Ceratocystis sensu stricto

Redefining Ceratocystis and allied genera

The genus Ceratocystis was established in 1890 and accommodates many important fungi. These include serious plant pathogens, significant insect symbionts and agents of timber degradation that result in substantial economic losses. Virtually since its type was described from sweet potatoes, the taxonomy of Ceratocystis has been confused and vigorously debated. In recent years, particulary during the last two decades, it has become very obvious that this genus includes a wide diversity of very different fungi. These have been roughly lumped together due to their similar morphological structures that have clearly evolved through convergent evolution linked to an insect-associated ecology. As has been true for many other groups of fungi, the emergence of DNA-based sequence data and associated phylogenetic inferences, have made it possible to robustly support very distinct boundaries defined by morphological characters and ecological differences. In this study, DNA-sequence data for three carefully selected gene regions (60S, LSU, MCM7) were generated for 79 species residing in the aggregate genus Ceratocystis sensu lato and these data were subjected to rigorous phylogenetic analyses. The results made it possible to distinguish seven major groups for which generic names have been chosen and descriptions either provided or emended. The emended genera included Ceratocystis sensu stricto, Chalaropsis, Endoconidiophora, Thielaviopsis, and Ambrosiella, while two new genera, Davidsoniella and Huntiella, were described. In total, 30 new combinations have been made. This major revision of the generic boundaries in the Ceratocystidaceae will simplify future treatments and work with an important group of fungi including distantly related species illogically aggregated under a single name.

Molecular and Pathogenic Characterization of Fusarium redolens, a New Causal Agent of Fusarium Yellows in Chickpea

The association of Fusarium redolens with wilting-like symptoms in chickpea in Lebanon, Morocco, Pakistan, and Spain is reported for the first time, together with the molecular and pathogenic characterization of isolates of the pathogen from chickpea of diverse geographic origin. Maximum parsimony analysis of sequences of the translation elongation factor 1α (TEF-1α) gene grouped all F. redolens isolates from chickpea in the same main clade. Pathogenicity assays using three chickpea cultivars and isolates from different geographic origins indicated that F. redolens is mildly virulent on chickpea. Moreover, infection of chickpea by F. redolens induces a disease syndrome similar to that caused by the yellowing pathotype of F. oxysporum f. sp. ciceris, including leaf yellowing and necrosis that develop upward from the stem base, and premature senescence of the plant. In contrast, F. redolens does not cause discoloration of the vascular tissues in chickpea but does cause brown necrotic lesions in the tap root and necrosis of lateral roots. F. redolens is not easily differentiated from F. oxysporum f. sp. ciceris using morphology-based diagnosis, and the two species cause similar symptoms on chickpea; therefore, the use of molecular protocols should help to avoid misdiagnoses of Fusarium yellows in chickpea.

Species-specific primers for Fusarium redolens and a PCR-RFLP technique to distinguish among three clades of Fusarium oxysporum

The currently available morphological and molecular diagnostic techniques for Fusarium redolens and the three phylogenetic clades of Fusarium oxysporum are problematic. Aligned translation elongation factor 1 alpha (TEF-1 alpha) gene sequences from these species and their close relatives were used to design F. redolens-specific primers, and to identify restriction sites that discriminate among the three clades of F. oxysporum. The F. redolens-specific primers distinguished this species from all others included in the study. There were three TEF-1 alpha-RFLP patterns among formae speciales of F. oxysporum. These PCR-RFLP patterns corresponded with the three clades. These techniques provide simple and inexpensive diagnostic methods for the identification of F. redolens and members of the three clades of F. oxysporum.

Species Delimitation and Host Specialization of Ceratocystis laricicola and C. polonica to Larch and Spruce

Ceratocystis laricicola and C. polonica are fungal symbionts of bark beetle species of the genus Ips that attack species of Larix and Picea, respectively, across Eurasia. Earlier studies found that these fungal species were morphologically identical, had similar isozymes patterns, and had identical internal transcribed spacer (ITS) sequences of the rDNA operon. We analyzed 27 isolates from Europe, southwestern Siberia (Russia) and Japan, representing the known geographic ranges of the two species. Phylogenetic analysis of the DNA sequences of a portion of the MAT-2 idiomorph showed these species to be distinct, with the Japanese isolates of C. laricicola having a sequence slightly different (5 bp) from those of the Russian and European isolates of C. laricicola. Sexual compatibility tests showed full interfertility among isolates of C. polonica from Europe, Russia and Japan, but isolates of C. polonica were not fully interfertile with isolates of C. laricicola. A Russian and a European isolate of C. laricicola mated with each other but not with the Japanese isolates of C. laricicola. Mature L. sibirica and P. obovata were inoculated with isolates of C. laricicola and C. polonica from Europe, Russia, and Japan, and measurement of lesions in the inner bark/cambium region demonstrated strong host specialization. The data suggest that the two fungal species are very closely related and are distinguished primarily by their physiological specialization to the hosts of their bark beetle vectors.

The root rot fungus Armillaria mellea introduced into South Africa by early Dutch settlers

Dead and dying oak (Quercus) and numerous other woody ornamental trees and shrubs showing signs and symptoms of Armillaria root rot were identified in the Company Gardens, Cape Town, South Africa, which were established in the mid-1600s by the Dutch East Indies Trading Company. Nineteen isolates from dying trees or from mushrooms were collected and analysed to identify and characterize the Armillaria sp. responsible for the disease. The AluI digestion of the amplified product of the first intergenic spacer region (IGS-1) of the rRNA operon of 19 isolates from the Company Gardens was identical to that of some of the European isolates of A. mellea s. s. The IGS-1 region and the internal transcribed spacers (ITS) were sequenced for some of the Cape Town isolates. Phylogenetic analyses placed the Cape Town isolates in the European clade of A. mellea, which is distinct from the Asian and North American clades of this species. Identification based on sexual compatibility was conducted using A. mellea tester strains in diploid-haploid pairings, which showed some compatibility between the Cape Town isolates and testers from Europe. Somatic compatibility tests (diploid-diploid pairings) and DNA fingerprinting with multilocus, microsatellite probes indicated that the Cape Town isolates were genetically identical and may have resulted from vegetative (clonal) spread from a single focus in the centre of the original Company Gardens (c. 1652). The colonized area is at least 345 m in diameter. Assuming a linear spread rate underground of 0.3 m/year to 1.6 m/year, the genet (clone) was estimated to be between 108 and 575 years old. These data suggest that A. mellea was introduced into Cape Town from Europe, perhaps on potted plants, such as grapes or citrus, planted in the Company Gardens more than 300 years ago.

Characterization of Sphaeropsis sapinea Isolates from South Africa, Mexico, and Indonesia

Post-hail-associated dieback of Pinus patula and P. radiata trees, induced by Sphaeropsis sapinea (=Diplodia pinea), is a common and important disease in commercial pine plantations. Two morphotypes, A and B, have been described for this fungus based on differences in cultural characteristics, conidial morphology, and virulence among isolates from the north central United States. The existence of the two described morphotypes was later verified through the use of random amplified polymorphic DNA (RAPD) analyses, and the morphotypes were designated as the A and B RAPD marker groups. The objective of this study was to characterize a set of S. sapinea isolates from South Africa, Indonesia, and Mexico using RAPD analysis and DNA sequencing of the internal transcribed spacer (ITS) region of the ribosomal DNA operon. Sizes of conidia and culture morphology were, furthermore, used to compare the three groups of S. sapinea isolates that emerged from the RAPD analysis. Two of the RAPD groups included isolates from the United States, representing the A and B morphotypes, while the third RAPD group accommodated Indonesian and one Mexican isolate. ITS sequences of all the S. sapinea isolates were highly homologous and resolved only the A and B RAPD groups. The ITS sequences of the isolates in the third RAPD group were the same as those of the A RAPD group. Conidia of isolates representing the A and B morphotypes were approximately the same size, but those of the third RAPD group were significantly longer. RAPD analysis enabled us to identify a third group of S. sapinea that is different from the well-recognized A and B groups. Isolates in this third RAPD group also have a distinct morphological characteristic and thus represent a third discrete morphological group, which we refer to as the C morphotype of S. sapinea.

Pathogenicity of four blue-stain fungi associated with aggressive and nonaggressive bark beetles

ABSTRACT The pathogenicity of two isolates of each of four bark beetle-associated blue-stain fungi was evaluated after mass inoculation of about 40-year-old Norway spruce trees (Picea abies). Trees were inoculated with a different isolate of each fungus in 1995 and 1996 at a density of 400 inoculations per m(2) in a 1.2-m-wide band on the lower bole (about 270 inoculations per tree). Trees were felled 15 weeks after inoculation. In 1995, Ceratocystis polonica was the only fungus that had stained the sapwood (56.3% of cross-sectional sapwood area). It induced five times longer phloem necroses, 21 times more dead cambium, and 11 times more dead phloem than any other fungus. In 1996, C. polonica induced less extensive host symptoms and an unidentified Ambrosiella sp. induced comparable symptoms to C. polonica in the phloem and cambium. No trees showed any foliar symptoms 15 weeks after inoculation, but six out of eight trees inoculated with C. polonica in 1995 had only 0 to 25% functional sapwood and probably would have died if felling had been delayed. This study confirms that C. polonica, an associate of the aggressive bark beetle Ips typographus, is pathogenic to Norway spruce. The pathogenicity of the Ambrosiella sp., which is associated with a nonaggressive bark beetle, seems moderate and varies between isolates. The two remaining fungi included in this study (Ophiostoma piceae and a dark fungus with sterile mycelium), which are associated with nonaggressive bark beetles, were nonpathogenic in both experiments. These results are consistent with the hypothesis that aggressive bark beetle species vector virulent fungi that may help them kill trees, but the results also show that some nonaggressive bark beetles may vector phytopathogenic fungi.

A new species of Ophiostoma from North America, similar to Ophiostoma penicillatum

Ophiostomatoid fungi that resemble Ophiostoma penicillatum were isolated from insect-infested spruce (Picea sp.) in Japan as well as Larix decidua Mill. (European larch) in North America. Isolates were characterized based on morphology and could be separated into two distinct groups. Those from spruce in Japan represent O. penicillatum, and are characterized by allantoid, slightly curved conidia. The North American isolates from Larix decidua are of a previously undescribed species, characterized by long, narrow conidia. The latter fungus is described as Ophiostoma americanum with an anamorph, Leptographium americanum. Key words: Ophiostoma penicillatum, Ips typographus, Ophiostoma americanum, Dendroctonus simplex, Larix decidua.

Growth of four bark-beetle-associated blue-stain fungi in relation to the induced wound response in Norway spruce

Twenty-five-year-old Norway spruce trees (Picea abies) were inoculated with four blue-stain fungi. Each tree was inoculated three times with each fungus and three times with sterile agar as a control, giving a total of 15 inoculations per tree. There was little variation in the extent of phloem necrosis produced in response to the different fungi, but 5 weeks after inoculation necroses induced by Ceratocystis polonica and Ambrosiella sp. were significantly longer than those for the other fungi. At the same time, C. polonica had induced sapwood desiccation twice as deeply into the wood as any other fungus. Hyphal growth of the fungi into phloem and sapwood followed the same pattern as necrosis length and desiccation depth. Five weeks after inoculation, C. polonica had penetrated phloem and sapwood farther than any other fungus. It grew more slowly than the other fungi in both tissues the first week after inoculation, but the four following weeks it grew more quickly than all other fungi. Key words: Ambrosiella, blue-stain fungi, Ceratocystis polonica, low-density inoculation, Ophiostoma piceae, Scolytidae.