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Quantification of Botrytis and Laccase in Winegrapes

¹ Research specialist, Department of Viticulture and Enology, University of California, Davis, CA 95616 (current address: Department of Plant Sciences, University of Oxford, OX1 3RB, UK), ² Student, Department of Viticulture and Enology, University of California, Davis, CA 95616, ³ Research scientist, ETS Laboratories, St. Helena, CA 95474 (formerly with E. & J. Gallo Winery, Modesto, CA).

^* Corresponding author (email: molly{at}fmdewey.com)

The levels of rot in approximately 2,000 samples of winegrapes harvested from the Central Valley, California, in 2005 and 2006 were determined by hand sorting of berries and by quantitative immunoassays for Botrytis antigens in the expressed juice. The levels of Botrytis were compared with laccase activities in the same juice samples. A Botrytis-genus-specific, monoclonal antibody (BC-12.CA4) was used to quantify Botrytis by a plate-trapped antigen ELISA and by a new immunochromatographic assay (lateral flow device). Standards for immunoassays on juice samples were prepared from hand-picked, carefully sorted, naturally infected and uninfected Chardonnay grapes. Percentage rot was expressed on the basis of weight and number of infected berries. Use of alternate antigen standards including extracts from freeze-dried mycelium from cultures of Botrytis grown on grape juice and dilutions of a specific Botrytis dessert wine were investigated. Laccase activities were determined by an SO₂-independent, high-throughput method. There was poor correlation between hand-sort estimates of rot from machine-harvested grapes graded at the test stands at wineries with immunoassays for Botrytis antigens and tests for laccase activities in juice samples. However, better correlation (R² = 0.7217) was found between laccase and levels of Botrytis-rot in juice samples from selected, carefully sorted hand-picked berries and immunoassays. The level and frequency of laccase in juice samples increased notably toward the end of the harvest season. In 2005 laccase was most commonly found in juice from Chardonnay, Syrah, and Zinfandel grapes and in 2006 in juice from Cabernet Sauvignon and Merlot.

Key words: Botrytis cinerea, table wines, laccase, diphenol oxidoreductase