Paclobutrazol modifies tree vigour and flowering in mango cv. alphonso

Cumulative effects of three annual soil drenching treatments of paclobutrazol (5 and 10 a.i. g/tree) given to the mango cv. Alphonso during months of Aug–Sept revealed reduction in tree height, mean shoot length and number of dormant shoots, and enhancement in flowering. Between the treatments, 10 g/tree paclobutrazol treatment was more effective in altering the vigour determining morphological characters. Flowering intensity did not differ much between the two treatments. The anatomical features under paclobutrazol treatment (10 g a.i./tree) revealed higher phloem to xylem ratio; more so in the shoots of current year flush than the previous year ones. Xylem sap volume declined with the paclobutrazol treatment. The paclobutrazol treated trees responded with an enhancement in the levels of abscisic acid (ABA) and cytokinin-zeatin riboside (t-ZR) and dihydtozeatin riboside (DHZR) in the xylem sap and leaves, and phenols in leaves concomitant with the decline in leaCindole acetic acid (IAA) content; changes being greater under higher dose of paclobutrazol. These results show that the paclobutrazol induced inhibition in tree vigour and promotion of flowering in mango is not only associated with the gibberellin biosynthesis inhibiting character of paclobutrazol but also with its influence on other hormones such as ABA, cytokinins and IAA and as also on phenol.