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Abstract
Botryosphaeriaceae are important pathogens on a variety of woody hosts, including almond, a major crop in California. Almond is susceptible to Botryosphaeria dothidea that forms band cankers on almond trunks, and the same fungus was also isolated from cankers of the canopy. To study the diversity and host range of B. dothidea and allied species from almond we used 132 isolates from 36 plant hosts from five continents, including 45 strains from almond in California. Species were identified by comparison to 13 ex-type strains with phylogenetic analyses based on six loci, including the internal transcribed spacer (ITS) regions of the nuclear ribosomal RNA gene repeat and portions of the coding genes elongation factor 1-alpha, glyceraldehyde-3-phosphate dehydrogenase, heat shock protein, histone-3 and beta-tubulin. Seven species were found from almond: Botryosphaeria dothidea, Neofusicoccum parvum, Neof. mediterraneum, Neof. nonquaesitum, Diplodia seriata and Macrophomina phaseolina were identified from band cankers, and B. dothidea, Neof. mediterraneum, Neof. parvum and Dothiorella sarmentorum from canopy cankers. All were capable of inducing cankers on inoculated almond branches in the field. All species found on almond also occurred on other hosts, suggesting that infected vegetation adjacent to almond orchards could serve as source of inoculum of virulent almond strains. Of the 19 monophyletic groups obtained at the species level, 13 contained ex-type strains, five were morphologically similar to established species and one was morphologically distinct from its closest relatives, Neof. andinum and Neof. arbuti, as well as from the more than 190 described species of Fusicoccum and Neofusicoccum, and thus was described as the new species, Neof. nonquaesitum. Evidence for cryptic speciation was found in B. dothidea, Neof. ribis and Spencermartinsia viticola. Botryosphaeria dothidea and Neof. ribis comprised lineages that formed the morphologically distinct Dichomera anamorph not found in any other isolates recognized as B. dothidea and Neof. ribis. An S. viticola isolate from California was phylogenetically divergent and had conidia that differed morphologically from the type. Neofusicoccum parvum was diverse but lacked any morphological features correlating with molecular diversity. Phylogenetic analyses of combinations of datasets showed that pooled analyses of all six datasets resulted in the highest number of supported branches, suggesting that addition of more data might yet improve phylogenetic resolution.
We thank Mike Wingfield and Bernard Slippers, FABI, University of Pretoria, Nuccia Eyres, Department of Agriculture, government of Western Australia, Turner Sutton, North Carolina State University, and Bernardo Latorre, Pontificia Universidad Católica de Chile, for providing cultures critical to this work, Dave Morgan, UC Davis, for suggestions that improved the manuscript, and the California Almond Board for financial support.