EFFECT OF UNICONAZOLE ON FLOWERING, YIELD AND FRUIT QUALITY ON DURIAN

Abstract

This study was aimed to investigate the effect of uniconazole (UCZ) on inducing early flowering, fruit yield and quality in durian cultivar ‘Monthong’. In the 1st year, a single foliar spray at a high concentration of 2,500 mg L-1 UCZ was made, compared to multiply sprays of 1.5 mg L-1 brown seaweed extracts, a conventionally used solution. The results showed that UCZ sprayed at mature leaf stage after 2nd leaf flushing could hasten flower emergence. UCZ very strongly inhibited inflorescence length, shortening the fruit stalk. There was no significant effect of UCZ on fruit yield but UCZ reduced fruit size. Analysis of fresh fruit showed that UCZ decreased both fresh weight and normal seeds. In vivo pollen germination, observation showed that UCZ delayed pollen tube growth. In the 2nd year, the experiment was conducted to find a suitable concentration for early durian fruiting. Lower concentrations of UCZ could induce both early flowering and more flowering branches than non-chemical application. All lower concentrations of UCZ had no effect on fruit yield. Spraying of 100 mg L-1 UCZ had no effect on suppression of inflorescence elongation and fruit size. UCZ at 250 and 500 mg L-1 inhibited only fruit width, whereas no other fruit size characteristics were suppressed. All lower concentration of UCZ decreased both fresh weight and the number of normal seeds. These results suggest that UCZ promoted flowering in durian by shortening the time of bud release. The reduction of pollen tube growths caused by UCZ could be attributed to the inhibition of normal seed development. We recommended the lower concentration of UCZ at 100 mg L-1 for early durian production.