Pre-harvest glochid abscission induced by spraying of GA3 and ethephon on fruits of cactus pear (Opuntia spp.)

Glochids are fine, sharp, sclerified thorns composed of pure crystalline cellulose. The presence of these small spines negatively affects harvest, fruit quality and acceptance; therefore, it is necessary to remove them. At present, glochids are removed by placing the fruits on the ground where they are swept with a broom or a bundle of twigs, or by machines. However, these techniques cause mechanical damage and postharvest losses. Another option is the use of growth regulators before harvest, which has had medium success on white cactus pear. However, the particular effect that these regulators may have on glochid abscission and postharvest physiology and quality in other Mexican varieties has not been studied. In this research, the effect of GA(3) and Ethephon on glochid abscission (pre- and post-harvest) and on postharvest fruit quality was evaluated in four cactus pear varieties: Solferino, Rojo 3589, Amarillo 2289, and Rojo Vigor. At anthesis, flowers and fruits were sprayed with 4 or 6 consecutive (weekly) applications of GA(3) (50 or 100 ppm) and, later, 4 or 6 consecutive (weekly) applications of Ethephon (700 to 900 ppm). After harvest, the following variables were measured: fruit weight, peel, pulp seed, juice degrees Brix, firmness and color. The varieties showed natural differences in the number of glochids per areole, areole glochid retention force, and as response to the treatments. Before harvest, the highest (82%) and lowest (70%) average glochid abscission were observed in the Amarillo 2289 and Solferino varieties, respectively. After harvest, the highest abscission (97.3%) was observed in the Solferino, Rojo 3589 and Amarillo 2289 varieties, and the lowest abscission (92%) in the Rojo Vigor variety. The high GA(3) concentration (100 ppm) promoted higher abscission of glochids than the lower concentration (50 ppm). An antagonistic effect was observed between the factors GA(3) concentration and number of applications. Before harvest, none of the other factors had a differential effect on this variable, except the variety factor. In general, the treatment that promoted the highest glochid abscission, before (82.25%) and after (97.25%) harvest, was four applications of GA(3) (100 ppm) and four applications of Ethephon (700 ppm). In general, the application of GA(3) and Ethephon improved fruit quality parameters, although in certain varieties, some of the quality parameters were affected negatively by some of the treatments.