THE IMPORTANCE OF ADVISORY SERVICE IN PREDICTING BITTER PIT USING EARLY-SEASON FRUIT ANALYSIS

Bitter pit is a physiological disorder of apple (Malus × domestica) fruit that is influenced by fruit calcium (Ca) and potassium (K) status. The incidence of bitter pit usually can be reduced by foliar application of Ca during the growing season. Early-season fruit mineral analysis is a technique for predicting fruit K/Ca ratio at harvest, which can serve as a surrogate index for risk of bitter pit development. Early diagnosis of probable high fruit K/Ca at harvest would allow growers to take measures to lower the fruit K/Ca ratio and thereby reduce bitter pit risk. This work focused on verifying the applicability to Trentino apple orchards of the method of early-season fruit analysis used in the South Tyrol to predict bitter pit risk. The survey results acquired during the 1999-2004 growing seasons showed significant differences among cultivars and locations, which allowed development of provisional reference ranges for fruit Ca concentration and K/Ca concentration ratios. Bitter pit incidence and fruit K/Ca ratio were positively related but varied with cultivar, suggesting that cultivar-specific critical values for the K/Ca ratio are necessary. The results suggest that it is possible to accurately predict bitter pit incidence at harvest and stress the need for additional bitter pit management practices based on relevant data collection and interpretation by a local Advisory Service. Cultivar- and site-specific Ca spray programs are recommended to help prevent bitter pit development.