Effect of pre-flowering irrigation on leaf photosynthesis, whole-tree water use and fruit yield of mango trees receiving two flowering treatments

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Two flowering treatments and two irrigation treatments were applied to mango trees of cultivar Kensington Pride in a commercial orchard near Darwin, northern Australia. Paclobutrazol (PBZ) was applied as a soil drench. For the mango flowering treatment (MFT) a cincture was cut into each tree trunk and a length of twine soaked in a solution of morphactin was tied into the cincture. Extra irrigation treatment (XTI) was applied between 30 and 46 days before peak flowering, and normal irrigation (NI) was applied when flowering activity was detected in about 65% of the tree canopy. Leaf light-saturated carbon assimilation ( A lsat), stomatal conductance ( g s), chlorophyll fluorescence parameters, whole-tree water use, flowering activity, fruit growth and fruit yield were recorded over three years. A lsat, g s, and electron transport rates (ETR) were low at time of flowering regardless of the irrigation or flowering treatment. A significant increase in A lsat, and g s (10–20%) was detected at some dates in trees receiving extra irrigation. ETR of XTI trees was significantly higher than that of NI trees at flowering and during early phase of fruit growth, but not later in the season. In both flowering treatments whole-tree water use of XTI trees was significantly higher than that of NI trees in the pre-flowering and flowering period but not near the end of the fruiting season. XTI treatment did not change flowering intensity; however, it caused flowering to be more variable. XTI treatment resulted in larger fruits in PBZ treated trees and increased fruit retention in MFT treated trees. Fruit relative growth rate was higher in fruits from XTI trees early in the season but was similar to those from NI trees later in the season. Regression analysis of the proportion of flowering and fruit number/yield during the 3 years of the experiment reflected a similar conversion of flowers to fruits in the M-XTI and all PBZ trees, but was lower in the M-NI trees. After 3 years of treatment, XTI resulted in trees with larger trunk circumference and higher leaf area index compared to NI trees. The effect of low C availability at time of flowering on fruit yield is discussed.