Relationships between maturity and storage disorders in ‘cox’s orange pippin’ apples as influenced by preharvest calcium or ethephon sprays

Abstract

In a study over four growing seasons, changes in the starch pattern index, flesh firmness, and background colour were measured in ‘Cox’s Orange Pippin’ apples harvested at 3–4-day intervals during fruit maturation, and related to quality and storage disorders of fruit stored at 3°C for 6 weeks. Trees were sprayed with normal therapeutic sprays without Ca salts, or with Ca(NO3)2 at 2-week intervals during the growing season. Calcium-sprayed fruit showed small but consistent delays in fruit maturity compared with unsprayed fruit, as determined by starch pattern indices and background colour, but not by flesh firmness. After storage, Ca-sprayed fruit were firmer than unsprayed fruit, but there was no effect on background colour. Unsprayed fruit that were harvested early had a high incidence of bitter pit which decreased as harvest date was delayed. Unsprayed fruit were more susceptible to senescent breakdown as harvest date was delayed in two out of the four years. Calcium sprays reduced both disorders. In two seasons, trees were also sprayed with ethephon (2-chloroethyl-phosphonicacid) once before harvest Ethephon accelerated changes in all maturity parameters, decreased bitter pit in one year and enhanced senescent breakdown in both years. In orchard surveys of 35 and 51 orchards in 1980 and 1981 respectively, the possibility that variation in the incidence of bitter pit at any one Ca level resulted from differences in fruit maturity was tested. However, inclusion of starch pattern indices into regressions of bitter pit against Ca concentration in fruit did not improve the relationship between the two variables. Results indicate that starch pattern indices may be useful in following changes in fruit maturation, but cannot be used to predict risk of fruit to bitter pit and senescent breakdown. Adequate Ca levels in the fruit apparendy influence these disorders more than maturity. © Crown 1989.