Diversity of Diaporthe species causing wood-canker diseases of fruit and nuts crops in northern California
D. LAWRENCE (1), R. Travadon (1), K. Baumgartner (2). (1) University of California-Davis, Davis, CA, U.S.A.; (2) USDA-ARS, Davis, CA, U.S.A.
<i>Diaporthe</i> species cause many plant diseases worldwide including dieback and the formation of cankers in the permanent woody structure of economically important crops such as apricots, almonds, and grape. This study aimed at revealing potential inoculum sources of <i>Diaporthe </i>species associated with Phomopsis dieback of grape in California, where cultivars of table grape are among the most susceptible. <i>Diaporthe</i> isolates were collected from wood cankers in vineyards, orchards (almond, apricot, pear), and from the wild host willow in riparian areas surrounding these cultivated crops. Morphological characterization based on colony growth rates (ranging from 12-80 mm after 8 days) and <i>alpha</i> conidia sizes (ranging from 5.6-11.2 × 1.9-4.4 µm) identified seven morphological groups. Nine species (<i>D</i>. <i>ambigua</i>, <i>D</i>. <i>ampelina</i>, <i>D</i>. <i>australafricana</i>, <i>D</i>. <i>chamaeropis</i>, <i>D</i>. <i>eres</i>, <i>D</i>. <i>foeniculina</i>, <i>D</i>. <i>nobilis</i>, <i>D</i>. <i>novem</i>, and <i>Diaporthe</i> sp. nov.) were revealed based on phylogenetic analysis of three loci (ITS, translation elongation factor 1-alpha, calmodulin). This includes the first report of <i>D</i>. <i>australafricana</i>, <i>D</i>. <i>chamaeropis</i>, <i>D</i>. <i>nobilis</i>, and <i>D</i>. <i>novem</i> in California vineyards, with <i>D</i>. <i>chamaeropis </i>reported on grape for the first time as well as the circumscription of a novel <i>Diaporthe </i>sp. isolated from willow. Pathogenicity testing on grape is currently underway to elucidate the role of all nine identified <i>Diaporthe</i> species in the etiology of Phomopsis dieback.
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