Bitter pit is a physiological disorder caused by calcium (Ca) deficiency in apples. However, recent publications have shown that bitter pit can be caused by an increase of gibberellins activity in the plant. This research was carried out to assess the effects of orchard spraying with prohexadione-calcium (ProCa) (an inhibitor of gibberellins synthesis) and gibberellin GA3 on vegetative growth of the trees and occurrence of bitter pit in the fruit. The experiment was conducted in an orchard located in São Joaquim, State of Santa Catarina (Southern Brazil), in 2009/2010. 'Catarina' and 'Fuji' apple trees were sprayed with water (control), ProCa and GA3 (both products at the dose of 319 mg L-1), at the petal fall stage (October 15, 2009), when shoots were 5-10 cm long, with treatments repeated after 20 days. The trees were evaluated in terms of chlorophyll content, area, dry mass and specific area of the leaves (in January/2010), and length of current season shoots and weight of shoots removed by winter pruning (in May/2010). Fruit were harvest at commercial maturity, cold stored (0±0.5ºC/90-95% RH) for four months, and then assessed for occurrence of bitter pit after five days of shelf life. In both cultivars, vegetative growth of the trees was reduced by ProCa and increased by GA3 in comparison to the control. 'Catarina' and 'Fuji' apples from trees treated with ProCa had lower occurrence of bitter pit after cold storage than the control treatment, as a result of lower contents of K, Mg and N, in relation to the Ca contents, assessed in the peel tissue of the fruit. On the other hand, the treatment with GA3 increased the occurrence of bitter pit compared to the control in both cultivars.
Malus domestica Borkh; prohexadione-calcium; anti-gibberellin; fruit; mineral composition; postharvest; physiological disorder
