Using Incidence of Botrytis cinerea in Kiwifruit Sepals and Receptacles to Predict Gray Mold Decay in Storage. Themis J. Michailides, Associate Plant Pathologist, University of California, Davis, Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier 93648. David P. Morgan, Staff Research Associate, Department of Plant Pathology, University of California, Davis, Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier 93648. Plant Dis 80:248. Accepted for publication 15 December 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0248.

A field-monitoring system has been developed to predict the incidence in storage of gray mold decay of kiwifruit caused by Botrytis cinerea. Kiwifruits were harvested from nine vineyards in 1993 and 1994, and their sepals and receptacles (stem ends) were surface sterilized and placed on acidified potato dextrose agar. The incidence of B. cinerea was determined after incubating dishes at 6 to 7°C for 6 days followed by 3 days at 23°C. At commercial harvest time, kiwi-fruits were harvested from these vineyards and stored at a controlled-atmosphere, cold (-0.5°C) facility. Postharvest gray mold was recorded after 3 and 5 months of storage. In both years, the incidence of sepal colonization decreased 3 months after fruit set and then increased until harvest time. In contrast, the incidence of receptacle colonization increased continuously from 4 and 1 months after fruit set until harvest in 1993 and 1994, respectively. In 1993, the relationship between incidence of B. cinerea in fruit sepals or receptacles and incidence of gray mold after 3 and 5 months of fruit storage was significant, as determined by linear regression, for most sampling dates from 4 months after fruit set until harvest. In 1994, all regressions were significant (R² = 0.55 - 0.96, P < 0.05 or <0.01) and for both years the best correlation was obtained with the samplings done 4 months after fruit set. Furthermore, for both years, low (<15%), medium (16 to 50%), and high (>50%) incidence of sepal or receptacle colonization by B. cinerea distinguished (predicted) the majority of the vineyards as having low (<2%), moderate (2 to 6%), and high (>6%) incidence of postharvest gray mold decay after 5 months of storage, respectively. In vineyards where the incidence of gray mold decay was low to moderate (<2% and up to 3.3%), one or two sprays of vinclozolin (at bloom and/or preharvest) did not significantly reduce the incidence of gray mold. However, preharvest spray(s) of vinclozolin applied 1 and/or 2 weeks before harvest in vineyards with high (>6%) incidence of gray mold significantly reduced fruit decay in storage