Some factors influencing storage ability of 'Jonagold' apples

In the years 1994-1998 samples of soil, leaves, fruitlets and fruits from 20-22 commercial orchards in Central Poland were analysed for minerals. Directly after fruit harvest, internal ethylene concentration, flesh firmness, soluble solids, starch index and mean fruit weight were determined. Additional apple samples from each orchard were infiltrated with MgCl2 solution, and after 7 days at 20degreesC, bitter pit-like symptoms were recorded. After 6 months in cold storage, fruit quality was evaluated. Among the physiological disorders bitter pit (BP) prevailed. Its frequency was usually correlated with K and Ca concentration and with K:Ca ratio in any analysed organ as well as with leaf N concentration and Mn concentration in leaves and fruitlets. At a leaf K concentration as low as 1.25% d.m., no more than 2% of apples should exhibit bitter pit. When leaf K reaches 2.2%, from 6 to 16% of apples would show bitter pit. Generally the K:Ca ratio seemed to be the best indicator of bitter pit occurrence. A K:Ca ratio above 28:1 is associated with more than 2% of apples affected by this disorder. Incidence of bitter pit-like symptoms induced by infiltration with magnesium chloride was positively correlated with true bitter pit in apples; the coefficient of determination was 61%. These results indicate that the number of bitter pit-like spots may be a useful tool to predict natural bitter pit development in storage.