First Report of Neofusicoccum australe, N. luteum, and N. parvum Associated With Avocado Branch Canker in California

Prevalence, Identity, Pathogenicity, and Infection Dynamics of Botryosphaeriaceae Causing Avocado Branch Canker in California

Botryosphaeria branch canker and dieback of avocado (Persea americana Mill.) has expanded in avocado-growing areas in recent years. Twenty-one avocado groves in the major producing regions of California were surveyed in 2018 and 2019. Monthly inoculations of wounded, green, and lignified branches of 'Hass' and 'Lamb Hass' were conducted. Botryosphaeriaceae were the predominant fungi recovered from cankered tissues collected across the surveyed traditional and high-density orchards and caused symptoms on all six sampled cultivars. These fungi were also recovered in asymptomatic twigs and other organs and thus exist as a potential reservoir for future infections. Molecular analyses of 173 isolates showed that Neofusicoccum luteum had the greatest incidences across sites and cultivars, with 83 and 29% recovered from Hass and Lamb Hass, respectively. Pathogenicity tests on excised (Hass, GEM, and Hass mutants) and attached shoots from potted (Hass) and mature avocado trees (Hass and Lamb Hass) showed that all species were pathogenic on wounded, green, and mature branches of the specified cultivars. Monthly inoculations of wounded, green, and lignified branches of Hass and Lamb Hass showed that both stem types were susceptible throughout the inoculation periods, regardless of the avocado phenological stage. In temperature-dependent growth and infection studies, growth of three points could vary during the growing season. Botryosphaeriaceae grown was higher between 20 and 30°C, but only Lasiodiplodia theobromae significantly grew and caused external lesions at 35°C. Lasiodiplodia theobromae also grew more on perseitol-amended media, all indicating its adaptation to warmer temperatures and capacity in metabolizing the avocado-produced sugar. Overall, this study extended our knowledge of the prevalence, identity, and pathogenicity of Botryosphaeriaceae on avocado cultivars, which will be useful to tailor management strategies.

Fungal Pathogens Associated with Aerial Symptoms of Avocado (Persea americana Mill.) in Tenerife (Canary Islands, Spain) Focused on Species of the Family Botryosphaeriaceae

Fungi of the family Botryosphaeriaceae are considered responsible for various symptoms in avocado such as dieback, external necrosis of branches and inflorescences, cankers on branches and trunks, or stem-end rot of fruits. In recent years, these problems are becoming more frequent in avocado orchards in the Canary Islands (Spain). This work includes the characterization of fungal species involved in these diseases, which were isolated from avocado crops in Tenerife Island between 2018 and 2022. A total of 158 vegetal samples were collected, from which 297 fungal isolates were culture-isolated. Fifty-two of them were selected according to their morphological features as representative isolates of Botryosphaeriaceae, and their molecular characterization was carried out, sequencing the ITS1-2 region as well as the β-tubulin and the elongation factor 1-alpha genes. Five species of Botryosphaeriaceae were isolated, including Neofusicoccum australe, N. cryptoaustrale/stellenboschiana, N. luteum, N. parvum, and Lasiodiplodia brasiliensis. This is the first time that L. brasiliensis has been associated with avocado dieback and that N. cryptoaustrale/stellenboschiana has been cited in avocado causing symptoms of dieback and stem-end rot. However, it was not possible to assign our isolates unequivocally to N. cryptoaustrale or N. stellenboschiana even additionally using the rpb2 marker for their molecular characterization. Botryosphaeriaceae family seem to be involved in avocado dieback, in the premature fall of fruits during their development in the field and in post-harvest damage in Tenerife, but further studies are needed to clarify the fungal pathogens associated with symptoms in relation to phenological plant growth stages or less frequently observed.

Anti-Pseudomonas aeruginosa activity of a C16-terpene dilactone isolated from the endophytic fungus Neofusicoccum luteum of Kigelia africana (Lam.)

Fungal endophytes have the capacity to biosynthesize secondary metabolites that are produced by their host plants. In this study, a dilactone terpenoid of C₁₆ architecture was isolated from the fungal endophytes of Kigeliaafricana, in our attempt to identify anti-Pseudomonasaeruginosa metabolites. Thirty-eight fungal isolates were cultured for biomolecule production over a period of thirty days. Extracts from three (ZF 34, ZF 52 and ZF 91) of the fungi showed good anti-P.aeruginosa activity, with ZF 52 presenting the best MIC of 19.53 µg/mL and was accordingly subjected to chromatographic separation. Based on nuclear magnetic resonance (NMR) spectroscopy, high resolution mass spectrometry and single crystal X-ray diffraction (XRD) analyses, the isolated compound was identified as a C₁₆-terpene dilactone, with a structure consistent with that of the known diterpene, CJ-14445. The isolated dilactone showed anti-P.aeruginosa activity with MIC of 0.61 µg/mL, signifying the antibacterial potential of the biomolecule. The bioactive fungal isolate (ZF 52) was identified as Neofusicoccumluteum based on genomic DNA sequencing. This is the first report of the endophyte N.luteum from K.africana and the first reported occurrence of CJ-14445 in the fungus.

Phylogenomics of Plant-Associated Botryosphaeriaceae Species

The Botryosphaeriaceae is a fungal family that includes many destructive vascular pathogens of woody plants (e.g., Botryosphaeria dieback of grape, Panicle blight of pistachio). Species in the genera Botryosphaeria, Diplodia, Dothiorella, Lasiodiplodia, Neofusicoccum, and Neoscytalidium attack a range of horticultural crops, but they vary in virulence and their abilities to infect their hosts via different infection courts (flowers, green shoots, woody twigs). Isolates of seventeen species, originating from symptomatic apricot, grape, pistachio, and walnut were tested for pathogenicity on grapevine wood after 4 months of incubation in potted plants in the greenhouse. Results revealed significant variation in virulence in terms of the length of the internal wood lesions caused by these seventeen species. Phylogenomic comparisons of the seventeen species of wood-colonizing fungi revealed clade-specific expansion of gene families representing putative virulence factors involved in toxin production and mobilization, wood degradation, and nutrient uptake. Statistical analyses of the evolution of the size of gene families revealed expansions of secondary metabolism and transporter gene families in Lasiodiplodia and of secreted cell wall degrading enzymes (CAZymes) in Botryosphaeria and Neofusicoccum genomes. In contrast, Diplodia, Dothiorella, and Neoscytalidium generally showed a contraction in the number of members of these gene families. Overall, species with expansions of gene families, such as secreted CAZymes, secondary metabolism, and transporters, were the most virulent (i.e., were associated with the largest lesions), based on our pathogenicity tests and published reports. This study represents the first comparative phylogenomic investigation into the evolution of possible virulence factors from diverse, cosmopolitan members of the Botryosphaeriaceae.

Mechanisms of severe dieback and mortality in a classically drought-tolerant shrubland species (Arctostaphylos glauca)

PREMISE

Mortality events involving drought and pathogens in natural plant systems are on the rise due to global climate change. In Santa Barbara, California, United States, big berry manzanita (Arctostaphylos glauca) has experienced canopy dieback related to a multi-year drought and infection from fungal pathogens in the Botryosphaeriaceae family. A greenhouse experiment was conducted using Neofusicoccum australe to test the specific influences of drought and fungal infection on A. glauca.

METHODS

A full factorial design was used to compare four treatment groups (drought + inoculation; drought - inoculation; watering + inoculation; and control: watering - inoculation). Data were collected for 10 weeks on stress symptoms, changes in leaf fluorescence and photosynthesis, and mortality.

RESULTS

Results indicated significant effects of watering and inoculation treatments on net photosynthesis, dark-adapted fluorescence, and disease symptom severity (P < 0.05), and a strong correlation was found between physiological decline and visible stress (P < 0.0001). Mortality differed between treatments, with all groups except for the control experiencing mortality (43% mortality in drought - inoculation, 83% in watering - inoculation, and 100% in drought + inoculation). A Kaplan-Meier survival analysis showed drought + inoculation to have the least estimated survivorship compared to all other treatment groups.

CONCLUSIONS

In addition to a possible synergistic interaction between drought and fungal infection in disease onset and mortality rates in A. glauca, these results indicate that young, non-drought-stressed plants are susceptible to mortality from N. australe infection, with important implications for the future of wildland shrub communities.

Toxicity of Recombinant Necrosis and Ethylene-Inducing Proteins (NLPs) from Neofusicoccum parvum

Neofusicoccum parvum is a fungal pathogen associated with a wide range of plant hosts. Despite being widely studied, the molecular mechanism of infection of N. parvum is still far from being understood. Analysis of N. parvum genome lead to the identification of six putative genes encoding necrosis and ethylene-inducing proteins (NLPs). The sequence of NLPs genes (NprvNep 1-6) were analyzed and four of the six NLP genes were successfully cloned, expressed in E. coli and purified by affinity chromatography. Pure recombinant proteins were characterized according to their phytotoxic and cytotoxic effects to tomato leaves and to mammalian Vero cells, respectively. These assays revealed that all NprvNeps tested are cytotoxic to Vero cells and also induce cell death in tomato leaves. NprvNep2 was the most toxic to Vero cells, followed by NprvNep1 and 3. NprvNep4 induced weaker, but, nevertheless, still significant toxic effects to Vero cells. A similar trend of toxicity was observed in tomato leaves: the most toxic was NprvNep 2 and the least toxic NprvNep 4. This study describes for the first time an overview of the NLP gene family of N. parvum and provides additional insights into its pathogenicity mechanism.

Characterization and Pathogenicity of Botryosphaeriaceae Species Obtained from Avocado Trees with Branch Canker and Dieback and from Avocado Fruit with Stem End Rot in Chile

Several species of the Botryosphaeriaceae family have been associated with branch canker, dieback, and stem end rot in avocado (Persea americana Mill.). In Chile, the incidence of diseases affecting the avocado tree increased from 2011 to 2016, which coincided with a severe drought that affected avocado production. Moreover, distant countries importing avocados from Chile also reported an increase of stem end rot of ripe avocados. Therefore, the aims of this study were to identify the pathogen species associated with branch canker, dieback, and stem end rot of avocado in Chile and to study their pathogenicity. This study was conducted between 2015 and 2016 in 'Hass' avocado orchards located in the main avocado-producing regions in Chile. A diverse collection of fungal species was recovered from both necrotic woody tissue and necrotic tissue on harvested ripe fruit. On the basis of morphology and phylogenetic analyses of the internal transcribed spacer region (ITS1-5.8S-ITS2) and the translation elongation factor 1-α (TEF1-α) gene, eight species in the Botryosphaeriaceae family were identified: Diplodia mutila, D. pseudoseriata, D. seriata, Dothiorella iberica, Lasiodiplodia theobromae, Neofusicoccum australe, N. nonquaesitum, and N. parvum. For each of these species, pathogenicity studies were conducted on 1-year-old healthy Hass avocado plants. All isolates produced brown gum exudate and caused necrosis in the vascular system 3 weeks after inoculation. N. nonquaesitum, N. parvum, and D. pseudoseriata were the most virulent species. Necrotic lesions and cavities with white mycelia near the peduncle union were observed on Hass avocado fruit inoculated postharvest. L. theobromae, N. australe, and N. parvum were significantly more virulent than the other tested species in the Botryosphaeriaceae family. This study identified and characterized the pathogenicity of Botryosphaeriaceae species in Chile, which will prove useful to future research on these pathogens directed at establishing effective control strategies in avocado.

Characterization and Pathogenicity of Botryosphaeriaceae Fungi Associated with Declining Urban Stands of Coast Redwood in California

Coast redwood (Sequoia sempervirens) is among the most widely planted landscape trees in California (CA) but is in decline outside its natural range due to factors including prolonged drought and plant pathogens. We investigated associations of Botryosphaeriaceae fungi with declining coast redwood trees throughout CA. More than 100 samples were collected from 11 coastal and inland locations in CA. Fifty-nine Botryosphaeria-like fungal strains were isolated and 18 were selected for further study. Phylogenetic analysis of ITS and EF-1α sequence data confirmed the presence of Botryosphaeria dothidea, Neofusicoccum australe, N. luteum, N. mediterraneum, and N. parvum. Pathogenicity testing showed that although the Neofusicoccum species vary in virulence, all are more virulent that B. dothidea. N. australe caused the largest lesions, followed by N. luteum, N. parvum, and N. mediterraneum. Of the species recovered, only B. dothidea has been previously confirmed as a pathogen of coast redwood in CA. These results confirm that multiple Botryosphaeriaceae species are associated with branch decline and dieback on coast redwood in CA, which agrees with similar studies on woody agricultural crops. Accurate diagnosis of fungal pathogens of coast redwood is important for the development of disease management strategies and may help improve horticultural practices in maintenance of urban stands.

Characterization and Pathogenicity of Botryosphaeriaceae Species Isolated from Almond Trees on the Island of Mallorca (Spain)

In this study, 31 almond orchards with trees showing severe decline symptoms were surveyed from 2009 to 2014 on the island of Mallorca (Spain). In all, 45 Botryosphaeriaceae isolates were collected and characterized based on phenotypical features and comparisons of DNA sequence data of the nuclear ribosomal DNA-internal transcribed spacer region and elongation factor 1-α gene. Five species were identified as Diplodia olivarum, D. seriata, Neofusicoccum luteum, N. mediterraneum, and N. parvum. Pathogenicity tests were performed on four cultivars ('Pons', 'Vivot', 'Jordi', and 'Ferragnes') under field conditions for two consecutive years (2013 to 2014), and confirmed that all five species cause canker and dieback of almond, with Neofusicoccum spp. more virulent than Diplodia spp. in both years. Jordi was less sensitive to fungal infection in 2013. First reports from almond in Spain include N. mediterraneum and N. luteum.

Botryosphaeriaceae species associated with dieback and canker disease of bay laurel in northern California with the description of Dothiorella californica sp. nov

Members of the Botryosphaeriaceae are cosmopolitan fungi that may exist as seemingly innocuous endophytes or as destructive pathogens of numerous woody hosts, including fruit and nut crops, urban ornamental trees and shrubs, and forest trees. Surveys of bay laurel in northern California have revealed symptoms of dieback and branch canker of unknown aetiology. The goals of this study were to identify and clarify the species of Botryosphaeriaceae associated with these symptoms and to confirm their pathogenicity. To understand the role of members of the Botryosphaeriaceae in the dieback and canker disease of bay laurel, 23 isolates were isolated from symptomatic wood. Phylogenetic analyses of ITS, translation elongation factor 1-α, and beta-tubulin revealed three species: Botryosphaeria dothidea, Neofusicoccum nonquaesitum, and the newly described and typified species Dothiorella californica sp. nov. When select isolates were inoculated to 2- to 3-year-old branches of Umbellularia californica in a natural forest, both B. dothidea and N. nonquaesitum were pathogenic with N. nonquaesitum producing the largest lesions at 12- and 18-months post inoculation, respectively, while Do. californica did not cause wood lesions significantly greater than the mock-inoculated controls. This study represents the first attempt to identify and test the pathogenicity of Botryosphaeriaceae species associated with dieback and canker disease of bay laurel in a northern California forest.

Biological and Molecular Characterization of Four Botryosphaeria Species Isolated from Pear Plants Showing Stem Wart and Stem Canker in China

Pear stem wart and pear stem canker, which have been considered as two different fungal diseases caused by pathogens belonging to Botryosphaeria spp., commonly occur and cause serious damage in the main pear-producing areas in China. To identify the species of this genus infecting pear in China, 131 Botryosphaeria isolates were recovered from pear samples exhibiting symptoms collected from 20 different provinces and areas. Morphological characterization and phylogenetic analyses of the ribosomal DNA internal transcribed spacer region and the β-tubulin and EF1-α genes revealed that Botryosphaeria dothidea, B. rhodina, B. obtusa, and B. parva were associated with different pear stem wart and stem canker symptoms. Remarkably, all isolates of B. dothidea were obtained from the samples showing either stem wart or stem canker lesions; however, the isolates of the other three species were obtained only from the samples showing stem canker. Pathogenicity tests on the pear shoots showed that B. dothidea isolates could induce stem wart or stem canker lesions but all the isolates of the other three species could only induce stem cankers. However, the isolates of B. parva, B. rhodina, and B. obtusa exhibited higher virulence than that of the B. dothidea isolates on the pear fruit. Our results suggest that B. dothidea is the common causal agent for these two diseases (a pear stem wart and a pear-related stem canker), whereas B. parva, B. rhodina, and B. obtusa only cause pear stem canker diseases. To our knowledge, this study represents the first report for biological and molecular characterization of four Botryosphaeria spp. isolated from pear plants showing stem wart and stem canker in China.

Phylogeny, Morphology, Distribution, and Pathogenicity of Botryosphaeriaceae and Diaporthaceae from English Walnut in California

Species of family Botryosphaeriaceae and genus Diaporthe (anamorph: genus Phomopsis, family Diaporthaceae) were reported and caused diseases on various fruit and nut trees in California. In the last several years, diseases on English walnut (Juglans regia) caused by species of Botryosphaeriaceae and Diaporthe were observed frequently in California. Disease symptoms include stem canker; shoot canker and blight; twig, leaf, and fruit blight; and necrotic leaf lesions. Isolates of the pathogen were collected from English walnut in 13 counties in California. The aims of this study were to identify these isolates and to test their pathogenicity to English walnut cultivars. In total, 159 California isolates were identified based on comparisons of DNA sequence data of the internal transcribed spacer, translation elongation factor 1-α, and β-tubulin gene regions, and combined with the morphological features of the cultures and conidia. Research results revealed that isolates represent 10 species of Botryosphaeriaceae and two species of Diaporthe. These species include Botryosphaeria dothidea, Diplodia mutila, D. seriata, Dothiorella iberica, Lasiodiplodia citricola, Neofusicoccum mediterraneum, N. nonquaesitum, N. parvum, N. vitifusiforme, Neoscytalidium dimidiatum, Diaporthe neotheicola, and D. rhusicola. Pathogenicity on three English walnut cultivars ('Chandler', 'Tulare', and 'Vina') using a mycelium plug inoculation method revealed that all these species are pathogenic to all the tested cultivars, with L. citricola and N. parvum being the most pathogenic species, followed by N. mediterraneum, N. dimidiatum, and B. dothidea. Chandler was more tolerant to infection than Tulare and Vina. Results in this study determined that multiple numbers of the Botryosphaeriaceae fungi and two Diaporthe spp. cause cankers and blights of English walnut and vary in their virulence from highly to slightly virulent, respectively.

The Botryosphaeriaceae: genera and species known from culture

In this paper we give an account of the genera and species in the Botryosphaeriaceae. We consider morphological characters alone as inadequate to define genera or identify species, given the confusion it has repeatedly introduced in the past, their variation during development, and inevitable overlap as representation grows. Thus it seems likely that all of the older taxa linked to the Botryosphaeriaceae, and for which cultures or DNA sequence data are not available, cannot be linked to the species in this family that are known from culture. Such older taxa will have to be disregarded for future use unless they are epitypified. We therefore focus this paper on the 17 genera that can now be recognised phylogenetically, which concentrates on the species that are presently known from culture. Included is a historical overview of the family, the morphological features that define the genera and species and detailed descriptions of the 17 genera and 110 species. Keys to the genera and species are also provided. Phylogenetic relationships of the genera are given in a multi-locus tree based on combined SSU, ITS, LSU, EF1-α and β-tubulin sequences. The morphological descriptions are supplemented by phylogenetic trees (ITS alone or ITS + EF1-α) for the species in each genus.

TAXONOMIC NOVELTIES

New species - Neofusicoccum batangarum Begoude, Jol. Roux & Slippers. New combinations - Botryosphaeria fabicerciana (S.F. Chen, D. Pavlic, M.J. Wingf. & X.D. Zhou) A.J.L. Phillips & A. Alves, Botryosphaeria ramosa (Pavlic, T.I. Burgess, M.J. Wingf.) A.J.L. Phillips & A. Alves, Cophinforma atrovirens (Mehl & Slippers) A. Alves & A.J.L. Phillips, Cophinforma mamane (D.E. Gardner) A.J.L. Phillips & A. Alves, Dothiorella pretoriensis (Jami, Gryzenh., Slippers & M.J. Wingf.) Abdollahz. & A.J.L. Phillips, Dothiorella thailandica (D.Q. Dai., J.K. Liu & K.D. Hyde) Abdollahz., A.J.L. Phillips & A. Alves, Dothiorella uruguayensis (C.A. Pérez, Blanchette, Slippers & M.J. Wingf.) Abdollahz. & A.J.L. Phillips, Lasiodiplodia lignicola (Ariyawansa, J.K. Liu & K.D. Hyde) A.J.L. Phillips, A. Alves & Abdollahz., Neoscytalidium hyalinum (C.K. Campb. & J.L. Mulder) A.J.L. Phillips, Groenewald & Crous, Sphaeropsis citrigena (A.J.L. Phillips, P.R. Johnst. & Pennycook) A.J.L. Phillips & A. Alves, Sphaeropsis eucalypticola (Doilom, J.K. Liu, & K.D. Hyde) A.J.L. Phillips, Sphaeropsis porosa (Van Niekerk & Crous) A.J.L. Phillips & A. Alves. Epitypification (basionym) - Sphaeria sapinea Fries. Neotypifications (basionyms) - Botryodiplodia theobromae Pat., Physalospora agaves Henn, Sphaeria atrovirens var. visci Alb. & Schwein.

Effect of Fungicide Application on the Management of Avocado Branch Canker (Formerly Dothiorella Canker) in California

Members of the Botryosphaeriaceae family have been associated with branch cankers of avocado trees (Persea americana) in California. Canker infections are initiated by spores entering the host plant through fresh wounds such as pruning wounds. With high-density planting becoming more common in the California avocado industry, more intensive pruning may increase the occurrence of branch canker. The objective of this study was to evaluate the preventive ability of some commercial fungicides belonging to different chemical families against fungal pathogens associated with avocado branch canker. Initially, 12 fungicides were tested in vitro for their effect on the inhibition of mycelial growth of three isolates of Dothiorella iberica and isolates (five per species) of Neofusicoccum australe, N. luteum, N. parvum, and Phomopsis sp. Subsequently, azoxystrobin, fludioxonil, metconazole, and pyraclostrobin, selected because of their low effective concentrations that reduce 50% of mycelial growth (EC₅₀ values), and myclobutanil, selected for its high EC₅₀ value, were tested in two field experiments. Azoxystrobin and fludioxonil were used in a premix with propiconazole and cyprodinil, respectively, in field trials. Significant differences (P < 0.05) were observed among fungicides in field trials. Azoxystrobin + propiconazole had the highest percent inhibition at 52 and 62% (internal lesion length) in trial 1 and trial 2, respectively, although this level of inhibition was not significantly different from that of metconazole. A significant correlation (r = 0.51, P < 0.05) was observed between internal lesion length data in the field experiment and EC₅₀ data from in vitro fungicide screening. Application of azoxystrobin + propiconazole and metconazole can play a key role in protecting Californian avocado against fungi causing avocado branch canker.

Spore Trapping and Pathogenicity of Fungi in the Botryosphaeriaceae and Diaporthaceae Associated with Avocado Branch Canker in California

Avocado branch canker in California is caused by a complex of fungal species in the families Botryosphaeriaceae and Diaporthaceae. As the popularity of avocado fruit increases, California growers are under pressure to increase their productivity in order to compete with imports. One way to increase production is through high-density planting, which entails intense canopy management, possibly leaving the trees vulnerable to infection through pruning wounds. A spore trap study was undertaken to determine the seasonal spore discharge of Botryosphaeriaceous and Diaporthaceous fungi. Based on colony counts, the highest population of Botryosphaeriaceous fungi (68%) occurred during or soon after precipitation events, which coincided with the winter months of December, January, and February. The spring and fall seasons had lower numbers of spores trapped (at 13 and 17%, respectively), with few spores trapped in the summer season. For members of the Diaporthaceae family, spores trapped were almost evenly split between winter and fall seasons (50 and 49%, respectively), with few to no spores trapped in the spring and summer seasons. A pathogenicity test of six fungi of Botryosphaeriaceae and one fungus of Diaporthaceae was conducted in the greenhouse. Internal plant vascular lesion lengths resulting from inoculation with any of the seven fungal species differed significantly from the noninoculated control. These studies suggest that pruning during the drier parts of the year would minimize infection by fungi in the Botryosphaeriaceae and Diaporthaceae families.

Botryosphaeriaceae Species Associated with Avocado Branch Cankers in California

Members of the family Botryosphaeriaceae cause branch cankers and dieback on California avocado trees. More intensive pruning, a practice associated with high-density planting that is becoming more common in the California avocado industry, may increase the occurrence of branch canker. This study was undertaken to identify and characterize the Botryosphaeriaceae spp. involved in the branch canker disease complex in order to develop future management strategies. From 2008 to 2009, branch cankers were sampled from four or five trees from each of eight avocado groves in five California counties. Six Botryosphaeriaceae spp. were identified based on morphology as well as phylogenetic analysis of the internal transcribed spacer region (ITS1-5.8S-ITS2) and a partial sequence of the β-tubulin gene. These six species included Neofusicoccum australe, N. luteum, N. parvum, an unknown Neofusicoccum sp., Fusicoccum aesculi, and Dothiorella iberica. Members of the Botryosphaeriaceae were isolated from all avocado-growing regions sampled in California; however, incidence and distribution of species varied. This report is the first description of the isolation of D. iberica from avocado branch cankers in California.

Effect of Temperature on Conidial Germination of Botryosphaeriaceae Species Infecting Grapevines

Germination of conidia of eight botryosphaeriaceous fungi infecting grapevines was evaluated after 2, 4, 6, 12, and 24 h incubation under eight different temperatures (5, 10, 15, 20, 25, 30, 35, and 40°C). The effect of temperature on conidial germination was also evaluated in different stages (hyaline versus pigmented conidia) of the species Lasiodiplodia theobromae. Conidial germination of Botryosphaeriaceae species infecting grapevines was significantly affected by temperature. Overall, conidial germination increased significantly with longer incubation times, especially from 2 to 12 h. In most cases, germination of conidia was not significantly different between 12 and 24 h incubation. Conidia of botryosphaeriaceous species did not germinate (with the exception of Botryosphaeria dothidea and Neofusicoccum parvum) at 5°C, and only B. dothidea, Diplodia seriata, and L. theobromae showed high levels of conidial germination at 40°C. Optimum conidial germination temperatures (defined as the temperature in which germination reached at least 50% in the shortest incubation time) were 25°C for B. dothidea and Dothiorella iberica, 25 to 30°C for Spencermartinsia viticola, 30°C for Diplodia corticola, D. mutila, D. seriata, N. parvum, and hyaline L. theobromae, and 40°C for pigmented L. theobromae conidia. Successful conidial germination of species of Botryosphaeriaceae infecting grapevines was always observed between 10 and 35°C with the exception of Dothiorella iberica and pigmented L. theobromae conidia, neither of which germinated at 35 and 10°C, respectively. Results of this study show conidia of botryosphaeriaceous species infecting grapevines to be capable of germination under a broad range of temperatures including those considered to be extreme, which may explain the success of these species as grapevine pathogens throughout most of the grape-growing areas in both Northern and Southern Hemispheres.