Evaluation of fruit detachment forces and related characteristics reveals differential fruit detachments at developmental stages and cultivar differences in cashew

Abstract

Cashew is an edible tree nut with great nutritional and industrial importance. Cashew fruit is unique because the true fruit (nut) grows attached to a swollen flower pedicel known as a hypocarp or cashew apple. The fruit detachment force (FDF), a quantitative measurement of the detachment of fruits from the stalk, is considered as an important parameter for the evaluation of the harvesting efficiency of machines, and the cultivar's potential for machine harvesting, and tolerances to biotic and abiotic stresses. There have been no studies on the evaluation of FDFs in cashew to date. In the current study, we investigated the detachment forces of fruits at ten different stages of development according to the BBCH (Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie) scale, a uniform coding system for different growth or phenological stages (701, 703, 705, 707, 709, 811, 813, 815, 817, 819) in ten cashew cultivars. Fruit weight (FW), FDF/FW ratio, and fruit firmness (FF) for different fruit development stages and fruit stalk scar area (SSA) of matured (819 stage) fruits were also studied. FDF, FW, FDW/FW and FF varied significantly at the different stages of fruit development among the studied cultivars. The FDF increased from 701 to 709 stages and then decreased from 709 to 819 stages in all the studied cultivars. The FDW/FW ratio reduced with the development and maturity of the fruit. In matured fruits (811–819 stages), FW and FF showed significant negative (p value = 0.028) and positive (p value = 0.015.) correlations, respectively, with the FDF. In contrast, the SSA had no significant influence on the FDFs. As the FDF has direct implications on the fruit removal efficiency, the results of this study will be useful for designing harvesting machines, screening genotypes for stress tolerance, and identifying the optimal harvesting stage in cashew.