Physiological persistence of paclobutrazol on the 'Tommy Atkins' mango (Mangifera indica L.) under rainfed conditions.
Salazar-García S., Vázquez-Valdivia V.
Author Affiliation: Campo Experimental Santiago Ixcuintla-CIRPAC-INIFAP, Apdo. Postal 100, Santiago Ixc., NAY 63300, Mexico.
Journal of Horticultural Science 72 : 339-345
Abstract : To investigate the feasibility of using paclobutrazol (PBZ) to control mango tree size chemically under rainfed conditions, the physiological persistence of soil applied PBZ on the vegetative growth, flowering behaviour, nutritional status, fruit set and quality of Tommy Atkins mango was assessed for 3 consecutive years in trials in San Blas county, Nayarit, Mexico. A single application of PBZ (0, 2.5, 5, 10, 15, 20 or 40 g/tree) was made after harvest in June, 1990. Each rate was dissolved in 2 litres of water and applied in a 15-cm-deep trench at 1.5 m around the tree. Shoot length was significantly reduced only with ?10 g PBZ/tree. PBZ at 20 and 40 g/tree markedly reduced vegetative growth for a year after treatment. The effect of 10 g PBZ/tree on shoot growth was modest and lasted one year. With the exception of 40 g PBZ/tree, the effect of any PBZ rate on shoot length disappeared by year 3. Increasing PBZ rate increased the earliness of flowering from 16 days (2.5 g PBZ/tree) to 40 days (40 g PBZ/tree) in the first year. For the second year after treatment, the effect of PBZ on time to flowering started to decline and, with the exception of 15 and 40 g PBZ/tree, early flowering ceased by year 3 after treatment. PBZ rates from 2.5 to 20 g/tree did not affect the number of mature fruits/m² of canopy during the 3 experimental years. PBZ at 40 g/tree resulted in the lowest production of mature fruits for the first 2 years after application. However, for the third year this treatment produced the most mature fruits/m² of canopy. All PBZ rates decreased average fruit weight, but the smallest fruits were produced with 15, 20 and 40 g PBZ/tree. Total soluble solids content of fruit juice was not affected at low PBZ rates (2.5 and 5 g/tree), but it was significantly higher with ?10 g PBZ/tree. PBZ at ?10 g/tree markedly reduced leaf P and Ca contents. A similar reduction was found for Mg with rates of ?15 g PBZ/tree. No significant changes were detected in the leaf content of N and K. The use of 10 g PBZ/tree may have a dual effect, as it may reduce tree size and induce early flowering. To keep this effect, it is speculated that under rainfed conditions, a single application of 10 g PBZ/tree should be followed by further application of 10 or 5 g/tree every 2 years.