2012 Annual Report 1a.Objectives (from AD-416): To study how K enters the berry and in what tissues it accumulates. To determine what is the sensitive phenological stage that is responsive to K. To study the influence of K on sugar translocation. To determine if K has effects on expression of genes in source and sink organs. To study applied aspects of the responses to K at the vineyard level. 1b.Approach (from AD-416): A combination of practical vineyard experiments evaluating the responses of grapes to potassium potassium applications including rates of maturation, internal quality, and control of preharvest and postharvest plant pathogens, combined with laboratory experiments evaluating the entry and spatial distribution of potassium within berries, gene expression by microarray analysis using the Nimblegen Grape array MD X 12 platform, and translocation of sugars. 3.Progress Report: Progress in FY 2012 was made on an objective of NP306, Problem Area 1d. Preservation and/or Enhancement of Quality and Marketability, Objective: Develop environmentally friendly strategies for plant and animal pathogen control. Potassium sorbate or a program consisting of four conventional fungicides were applied to clusters of ‘Thompson Seedless’ grapes at berry set, pre-bunch closure, veraison, and 2 or 3 weeks before harvest. After storage at 2ºC for 6 weeks, the natural incidence of postharvest gray mold was reduced significantly by potassium sorbate, the fungicide program, or both together in a tank mixture, in 2009 and 2010, but not in 2011, when little decay developed even after long storage of all these grapes. The experiment was repeated with the addition of three chitosan products (OII-YS, Chito Plant, and Armour-Zen). Potassium sorbate treatment significantly increased endochitinase activity and resveratrol content of the berry skin, indicating potassium sorbate had induced resistance to pathogen infection in the berries. Hydrogen peroxide content of the berries was significantly reduced by the chitosan products, but not by potassium sorbate or the fungicides. Only the fungicide treatment signiciantly reduced the prevalence of postharvest decay of berries. Among the conventional fungicides applied in this test, fenhexamid was markedly superior to the other fungicides for control of both the incidence and spread of gray mold during storage.