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Detecting and quantifying latent infection of canker- and blight-causing pathogens in stone fruit and nut crops in California

Paulo Lichtemberg: University of California - Davis

<div>Botryosphaeriaceae is considered as a fungal family consisting of plant pathogens, including a number of species causing canker and shoot blight diseases of woody plants. These pathogens cause latent infections of plant tissues. In order to quantify the latent infections of major canker-causing pathogens in different tree crops important in California, shoot and bud samples were randomly collected from almond, dried plum, pistachio, and walnut trees. The previously developed and used DNA primers and a <em>q</em>PCR assay were applied to process these samples to detect and quantify six selected canker-causing pathogen groups, such as <em>Phomopsis</em> spp., <em>Botryosphaeria dothidea, Lasiodiplodia</em> spp.<em>,</em> <em>Cytospora</em> spp.,<em> Neofusicoccum</em> spp., and<em> Diplodia </em>spp. The concepts of molecular severity (MS) and index of latent infection (ILI) were introduced and applied to quantify the levels of latent infection in these samples. Variation of incidence of latent infection among pathogen groups was observed, while, <em>Phomopsis</em> spp. and <em>Diplodia</em> spp. showed low levels as compared to those of other four pathogen groups. High incidences caused by <em>Cytospora</em> spp. were observed for two dried plum orchards, while most orchards showed high incidence of <em>B. dothidea</em> and <em>Lasiodiplodia</em> spp. and moderate levels caused by <em>Neofusicoccum</em> spp. The MS were maintained at a certain range among pathogen groups and tree crops. The ILI values were also variable among pathogen groups and tree crops.</div>