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Poster: Biology & Disease Mgmt: Postharvest Pathology & Mycotoxins


Seasonal population dynamics of mycotoxigenic Aspergillus section Nigri species on grapes and in vineyard soil using ddPCR
J. PALUMBO (1), T. O'Keeffe (1), M. Fidelibus (2) (1) USDA ARS, U.S.A.; (2) University of California, U.S.A.

Several species of Aspergillus section Nigri (black Aspergilli), including mycotoxin producers, are common residents of grape vineyards, but measuring relative population sizes of individual species using traditional isolation and identification methods is impractical. We developed species-specific primers and probes for quantitative droplet digital PCR (ddPCR) to simultaneously detect and quantify A. niger, A. carbonarius, A. welwitschiae and A. tubingensis populations from grape and soil samples. Samples were collected at berry set, veraison, harvest and raisin stages from two vineyards over two consecutive years. Plate counts showed that total fungal counts were 102-105 cfu/g on berries and 104-105 cfu/g in soil. Plate counts of black Aspergilli in soil were between 102 and 104 cfu/g, independent of sampling time, while counts of black Aspergilli on berries increased from <101 cfu/g at berry set to >103 cfu/g on raisins. Distribution of Aspergillus species using ddPCR showed that in soil, relative abundance of each species varied widely among samples, but A. niger was the most abundant species in 52 of 60 samples. On grapes, relative abundance of A. carbonarius was higher on mature grapes and raisins, and correlated with ochratoxin levels in those samples. This ddPCR method is a useful tool to describe fungal population dynamics in the environment and to monitor mycotoxigenic Aspergillus species during grape and raisin production.