Real-time PCR assay for the quantification of Botrytis cinerea in grapevine bunch trash

Effective Botrytis bunch rot (BBR) management requires the reduction of bunch trash colonization and the sporulation potential by Botrytis cinerea at flowering and behind (Fedele et al., 2017). In the scope to better understand BBR epidemiology and evaluate the efficacy of early-season disease control, colonization rate of B. cinerea was assessed in grapevine bunch trash by means of real-time PCR (qPCR). The qPCR assay was optimized to quantify B. cinerea DNA in the presence of Vitis vinifera DNA in bunch trash. The fungal colonization rate, namely Pathogen Coefficient (PC) (Saito et al. 2013), was calculated for an amount of B. cinerea conidia added into bunch trash. The PC value increased with the increase of B. cinerea DNA in the presence of V. vinifera DNA. Besides, the PC in different bunch trash infection categories estimated by qPCR were compared to plating method and microscopic counts to evaluate the incidence of colonized bunch trash and the sporulation potential. The obtained results establish the qPCR assay as a potential tool to examine the colonization rate of bunch trash. Hence, the PC was determined in field samples to compare the effect of different fungicide treatments for BBR control. This work provides a new method to be used in studies on B. cinerea in vineyards.