ASSESSMENT OF BITTER PIT RISK IN 'GALA' APPLES BY FRUIT INFILTRATION WITH MAGNESIUM

Abstract

Bitter pit is a postharvest physiological disorder of apples, related to Ca deficiency, and aggravated by high levels of Mg, N, and K in the fruit. This work was carried out to assess the viability of fruit infiltration with Mg for preharvest segregation of ‘Gala’ apples for risk of bitter pit development during cold storage. Fruits were sampled in 50 orchards located in southern Brazil in 2003. Samples of 25 fruits per orchard were taken about 20 days before commercial harvest maturity, vacuum infiltrated (100 mm Hg/2 min) in 0.1 M MgCl2 (with 0.3 M sorbitol and 0.05% Silwet L-77) and then assessed for incidence (%) of bitter pit like symptoms. Samples of 120 fruits were harvested in the same orchards, at the commercial maturity. In each of these samples, 100 fruits were stored in regular air cold storage for four months (0±0.5°C/90-95% RH) and 20 fruits were analyzed for mineral content (Ca, Mg, K, and N). Cold stored fruits were assessed for incidence of bitter pit 5 days after removal from storage. There was a close correspondence of critical levels of Ca and N in the fruit associated with the risk of bitter pit in both Mg-infiltrated and cold stored fruits sampled from different orchards. Orchards with Ca content 500 mg kg-1 in the fruit (corresponding to a N:Ca ratio >14) had higher incidence of bitter pit for both Mg-infiltrated and cold stored fruits. Also, there was a strong relationship between incidence of bitter pit in Mg-infiltrated and cold stored fruits. Thus, apple fruit infiltration with Mg is a feasible method to assess the orchard risk for bitter pit on 'Gala'.