RELATION BETWEEN WATER-SOLUBLE AND TOTAL Ca CONTENT AND BITTER PIT OCCURRENCE IN 'IDARED' APPLE

摘要

Bitter pit is a well-known physiological disorder in apple (Maius domestica Borkh.) caused mainly by low calcium content (De Long, 1936). Many reports claim calcium, to be the main factor causing bitter pit development (Ferguson et al., 1979; Martin et al., 1975; Pavicic, 1990; Pavicic and Miljkovic, 1991). However, other elements such as potassium or the ratio of mineral elements have also been reported to produce bitter pits (Schumacher et al., 1978). Ratios of elements such as N/Ca, K+Mg/Ca, K/Ca are sometimes used as indicators for predisposition to bitter pit development. Pavicic (1993) showed that chemical analysis of the fruit picked in optimal harvest time predicts bitter pit better than does leaf analysis. Threshold Ca levels above which physiological disorders will not develop (Meheriuk and Moyls, 1989) are not applicable in all cases. Calcium is not always connected with bitter pit incidence (Van Goor, 1971). Inconsistencies in the literature about the impact of calcium on bitter pit development suggest that only certain fractions of calcium are physiologically active (Saks et al., 1990; Van Lune and Van Goor, 1979). Such fractions are probably limited to water-soluble Ca and the ionically bound NaNO_3-exchangeable fractions (Himelrick, 1981). Water-soluble Ca is strongly associated with physiological disorders and this relation is not disturbed by season or harvest date (Saks et al., 1990). Therefore, we studied this fraction in fruit with and without bitter pit using 'Idared' grown on two rootstocks at four locations. Our objective was to see the relation between water-soluble Ca and total Ca in 'Idared' apple fruit and estimate the role this fraction plays in bitter pit development.