Author : Tuck-Thye Lye

Summary : Under normal environmental conditions, leaves and apices of 'Carabao' mango shoots produced small quantities of ethylene, ranging from 0.5 to 3 n1/cm apex length/hr in the apices, and 3.9 x 10(-8) l/sq.m. leaf area/hr in the middle leaves. Higher rates of ethylene production were found in the apical leaves than in the middle and basal leaves of the shoot. Foliar application of potassium nitrate did not increase ethylene production in the middle leaves of the shoot. In contrast, one to three days after potassium nitrate treatment, there was a detectable rise in ethylene in the shoot apex and it persisted even when floral development became visible. The flowering response of mango to potassium nitrate induction was distinctly localized; only treated shoots flowered while adjacent untreated shoots did not. The inductive action of the chemical was rapid, with the first visual signs of floral development appearing 6 to 8 days after treatment. Shoots with non-existent or underdeveloped apical buds were less responsive to floral induction. The presence of leaves was necessary for successful floral induction by potassium nitrate, although treating as few as three leaves per shoot was sufficient. There was a differential response to induction by leaves at different positions in the shoot - leaves in the middle region were responsive while the apical and basal leaves were not. There is evidence to suggest that a floral stimulus is produced in the leaves which act as receptive sites of action of potassium nitrate in floral induction. It is unlikely that potassium nitrate action is mediated directly by the increased production of ethylene in the leaves. Girdling experiments indicated that the floral stimulus must be transported from the leaves to the shoot apex.