PROHEXADIONE-CA MODIFIES GROWTH AND ENDOGENOUS HORMONES IN THE SHOOT APEX IN APPLE TREES

Abstract

This study was conducted with the purpose of learning the effects of prohexadione-Ca (P-Ca) on the vegetative and fruiting growth of the apple cv ‘Golden Delicious’ and relate these effects to the levels of endogenous gibberellins, cytokinins and auxins in shoot tips. The growth retardant was sprayed on trees early in the spring when shoot growth reached 5 cm in length. The concentration dosages of P-Ca were 0 (control), 125, 175 and 250 mg L -1 . The results showed that P-Ca at any concentration reduced the final length of shoots and internodes. The leaf number per shoot was also reduced in all P-Ca treated trees. The growth retardant at 175 and 250 mg L -1 increased total yield per tree, reflected by a higher fruit set but reduced, although not statistically, fruit weight. Harvested fruits from these treatments showed an increase in firmness and a reduction in soluble solids. The endogenous hormone status was analyzed by bioassay and GC-MS on shoot tips from apple trees treated with prohexadione-ca at 250 mg L -1 . The levels of gibberellins and auxins in shoot tips were decreased soon after the P-Ca application; whereas the cytokinin content increased. In these P-Ca tissues, it was possible to identify gibberellins A9, A20, A51 and A53. In control samples gibberellins A1, A4 and A7, were identified.