Quantification of<i>Botrytis cinerea</i>in Grapevine Bunch Trash by Real-Time PCR

Abstract

Quantification of colonization of grape bunch trash by <i>Botrytis cinerea</i> is crucial for Botrytis bunch rot (BBR) control. A previously developed quantitative polymerase chain reaction (qPCR) method was adapted to quantify <i>B. cinerea</i> DNA in grape bunch trash, and a colonization coefficient (CC) was calculated as the ratio between the DNA concentrations of <i>B. cinerea</i> and of <i>Vitis vinifera.</i> CC values increased linearly with the number of conidia of <i>B. cinerea</i> or the quantity of mycelium of <i>B. cinerea</i> added to the bunch trash increased. CC values also increased linearly in bunch trash samples containing increasing percentages of <i>B. cinerea</i>-colonized bunch trash; in the latter samples, CC values were correlated with subsequent assessments of <i>B. cinerea</i> colonization of trash (as determined by plating on agar) and sporulation on the trash (as determined by spore counts after incubation in humid chambers). The qPCR assay was also validated using trash collected from bunches treated or not treated with fungicides in three vineyards in two seasons. CC values reflected the reduction in sporulation and in latent infections of mature berries caused by fungicide application. The qPCR assay enables rapid, specific, sensitive, and reliable quantification of the degree of colonization of bunch trash by <i>B. cinerea</i>, which makes it a useful tool for studies of the epidemiology and management of BBR.