Preflower irrigation and paclobutrazol dependent fruit number and water use efficiency responses in young mango trees

Abstract

This study compared four rates of preflowering irrigation (0, 13, 25 and 50mm/week) on paclobutrazol (PBZ) and non-paclobutrazol (non-PBZ) treated mango trees ('Kensington Pride', KP) over four seasons (1995 to 1998). Flowering and fruit numbers per tree followed a biennial bearing pattern and the responses to preflower irrigation differed between PBZ and non-PBZ treated trees. Peak flowering intensity was significantly improved by PBZ application in one on-season and one off-season (1995 and 1998) and was reduced by 50 mm/week preflower irrigation in the same two seasons. There were significant interactions between irrigation and PBZ application for fruit number per tree for these two seasons. For the on-season of 1995 PBZ trees irrigated at 25 mm/week (78 fruit/tree) had significantly more fruit than all other PBZ and non-PBZ irrigation treatments with the exception of the non-PBZ, non-irrigated (0 mm/week) treatment. For the off-season of 1998 season PBZ trees irrigated at 13 mm/week produced 52 fruit/tree, significantly more than all other treatments. Year to year results were variable but highlighted that the greatest fruit production for PBZ treated trees came from low or moderate preflower irrigation rates and that the preflower irrigation requirements of PBZ treated trees are lower in off-seasons (13 mm/week) than on-seasons (25 mm/week) when they carry a greater fruit load. There was an overall pattern for PBZ treated trees with a low or moderate level of preflower irrigation to support the highest fruit numbers. Water use efficiency (WUE) defined as the sum of irrigation and rainfall over yield) values gave similar interactions to that of the fruit number results. The WUE results demonstrated that for non-PBZ treated trees preflower droughting was the most water efficient, but for PBZ treated trees it was more efficient to irrigate at 25 or 13 mm/week depending on the fruit loads of the season.