Chemical thinning of morula fruit (Sclerocarya birrea subspecies caffra Hochst) using benzyladenine

Abstract

A field experiment was conducted at Gabane Veld Product Research and Development (VPR&D) morula orchard from August 2008 to May 2009. to evaluate the effects of benzyladenine (BA) on fruit set and quality of morula (Selerocarya birrea subspecies caffra L.). Benzyladenine was applied when the fruitlets were 8-10 mm in diameter at concentrations of 0,50, 100 or 150 mg/1. Benzyladenine application significantly (p < 0.001) reduced fruit set of morula trees by between 48-67 %. Application of BA to morula fruit trees significantly (p < 0.001) increased fruit size (length and diameter), density and weight. However, BA application had no significant effect on the fruit length-to-diameter (L:D) ratio. Benzyladenine significantly (p < 0.01) increased the fruit endocarp but decreased mesocarp of morula fruit by a margin of (1.1-63 %), suggesting that BA-induced increase in fruit weight was attributed to increase in the endocarp. Application of BA to morula trees resulted in fruits with significantly higher soluble solids content (SSC) (p < 0.05), titratable acidity (p < 0.01), citric acid equivalent (p < 0.01) and vitamin c content (p < 0.001) compared to control (unsprayed) trees. Morula trees sprayed with BA had significantly (p < 0.001) higher leaf area, total leaf chlorophyll content, chlorophyll a and chlorophyll b respectively than unsprayed control trees. Benzyladenine application significantly (p < 0.05) increased vegetative growth (terminal shoot growth and number of shoots) of morula trees. Morula trees sprayed with BA had significantly higher leaf and fruit potassium, nitrogen, magnesium, calcium, sodium and phosphorus contents than control trees. Benzyladenine also promoted morula fruit colour development at maturation. The results of this study showed that BA has the potential to be used as a chemical thinner of morula or an agent that improves fruit quality. However, further research on concentration and timing of application needs to be done.