1a. Objectives (from AD-416):
To develop preharvest and postharvest practices to extend the shelf-life of table grapes. Specific objectives include: 1) assemble a large collection of Botrytis cinerea isolates from numerous vineyards in the San Joaquin Valley and determine their sensitivity to fungicides; 2) determine the effectiveness of fungicides applied at various times in vineyards before harvest on the incidence of summer bunch rot and subsequent decay after harvest; 3) determine residue levels and their persistence at harvest and during cold storage, and the influence of sulfur dioxide or ozone gas on their persistence; 4) evaluate the effectiveness of periodic or cyclic low concentration ozone use during cold storage (as opposed to constant low ozone concentration), with or without weekly sulfur dioxide fumigation, to control postharvest decay.
1b. Approach (from AD-416):
Isolates of Botrytis cinerea will be collected from table grape vineyards at various locations in the Central Valley of California. PCR will be performed using selected molecular makers to separate isolates into either genetic Group I or Group II. Selected isolates will be tested on agar media for sensitivity or resistance to selected fungicides. Fungicides applied at different timings before harvest in a commercial vineyard will be evaluated for control of summer bunch rot in the field and postharvest decay in berries during cold storage. Berry residue content and residue persistence of the selected fungicides will be determined. In addition to storage in air, the influence of ozone and sulfur dioxide fumigation on fungicide residues will also be determined.
3. Progress Report:
This Trust agreement was established to support Objectives 1 and 2 of the in-house project, Develop integrated and commercially feasible pre-and postharvest practices and treatments to maintain quality and extend the shelf and shipping life of fresh fruit (primarily citrus fruit and table grapes). After harvest, table grapes may be stored around 0C for a period of time prior to shipping to markets, but postharvest rots such as gray mold, if left uncontrolled, can cause significant economic losses during storage and in the market. This new project was initiated in May 2013, and the research focuses on the development of pre- and postharvest integrated approaches for control of postharvest rots in order to extend storage and shelf life of table grapes. A field experiment has been established to evaluate the use of reduced-risk fungicides in the field for control of postharvest gray mold. Isolates of the fungus Botrytis cinerea (the cause of gray mold) are being collected from various geographic areas. Research is ongoing to test sensitivity of Botrytis isolates to selected fungicides in order to develop relevant fungicide programs and evaluate the effectiveness of preharvest treatments alone or in combination with postharvest treatments such as fumigation with ozone or reduced sulfur dioxide for control of postharvest rots. The information will be used to develop integrated practices to improve the quality of table grapes grown in California.