Quantification of Botrytis in Grape Juice Determined by a Monoclonal Antibody-based Immunoassay

Abstract

Monoclonal antibodies to Botrytis//, raised in a previous study, were used to develop a plate—trapped antigen enzyme linked immunosorbent assay ( PTA-ELISA) to detect and quantify Botrytis antigens in juice from infected grapes. Using a dilution series of extracts from freezedried preparations of B. cinerea grown in liquid culture on grape juice and juice from artificially infected and healthy Cabernet Sauvignon and Semillon grapes, we have shown that BC-12.CA4, a genus-specific antibody, can be used in micro-titer PTA-ELISA tests to measure levels of infection from 0 to 5%. Forty-one samples of juice from 15 different cultivars from seven different wineries in the Central Valley region in California were tested along with juice from healthy-looking grapes of the same cultivars. No cross-reaction was found with any of the cultivars tested for juice from healthy-looking berries taken from loads with low levels of infection. Using BC-12.CA4 immunoassay levels of rot were generally higher than visual assessments of bunch rot particularly with machine-harvested grapes at the end of the season. However, in early season samples immunoassay estimates were, in some cases, lower than the visual assessments. It is strongly suspected that in the latter case fungi other than Botrytis were the main cause of bunch rot. Preliminary studies with another antibody, that recognizes both B. cinerea and Aspergillus niger, confirmed that the bunch rot in these cases was mostly due to fungi other than Botrytis.