The Role of Potassium in Quality of Grapes after Harvest
Commodity Protection and Quality
2013 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.
This agreement supports Objective 1 of the parent project, Evaluate pre-harvest practices and treatments for table grapes using substances of minimal environmental and dietary risk. Potassium sorbate or a program of four conventional fungicides were applied to clusters of ‘Thompson Seedless’ grapes at berry set, pre-bunch closure, onset of ripening, 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. Potassium sorbate treatment significantly increased endochitinase activity and resveratrol content of the berry skin, indications that the potassium sorbate had induced resistance to pathogen infection in the 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.