The aim of this thesis was to investigate how preharvest cultural factors such as calcium (Ca) sprays and fertiliser, leaf to fruit (leaf:fruit) ratios and water stress can influence the postharvest quality of tropical 'Kensington Pride' (syn. 'Kensington') mango (Mangifera in di ca L.) fruit. These four cultural practices chosen were also aimed at manipulating the Ca concentration in mango fruits to determine the role of fruit mineral nutrition, in particular Ca, in mango fruit ripening and storage potential.
The concentration of Ca in the fruit was directly manipulated by applying Ca directly to the fruit or the soil in a series of field experiments conducted in orchards at Ayr (north Queensland) and Childers (south east Queensland) between 1994 and 1996. Applying Ca directly to the fruit surface was more effective than applying Ca to the soil. In the 1994/95 season, JO uniform mango trees had fruits treated with 0 or 0.8% CaCl2 + 0.01% Agral at 45, 115 or 45 + 87 + 115 days after panicle emergence (DAPE). Control fruits were not treated. While the Ca concentration in the skin was significantly (P < 0.05) increased by 23-27% in all Ca-treated fruits, no significant (P < 0.05) difference in the number of days fruits took to reach eating soft at 22°C (shelf life) was observed. In the 1995196 season, the concentration of Ca in the spray solution was increased and the number of applications was increased to elicit a greater response in fruit shelf life. Fourteen uniform trees had fruits treated with 0, 2 or 4% CaCl2 + 0.01% Agral at weekly to fortnightly intervals from 4 weeks after flowering until fruit harvest. Control fruits were not treated. Both the 2 and 4% CaCl2 treatments significantly (P < 0.05) increased the pulp Ca concentration by approximately 18%. The Ca concentration in the skin was also significantly (P < 0.05) increased by 24 or 37% following treatment with 2 or 4% CaCl2, respectively. However, only the 4% CaCl2 treatment increased the fruit shelf life (1.3 days) and reduced the rate of fresh weight loss, but also caused a 5% increase in lenticel spotting.
While the aim to increase the concentration of Ca in the fruit was achieved, the fruit response (increased shelf life) was relatively minor for such an intensive application of Ca. Therefore, the following experiments aimed to manipulate the concentration of Ca in the fruit indirectly by altering the competition between leaves and fruits for photoassimilates (leaf to fruit ratio experiments) and irrigation water (water stress experiments) to investigate if indirect measures could more effectively influence fruit Ca, and thus produce a greater response in fruit shelf life.
The first of the two leaf:fruit ratio experiments was conducted during the 1 994195 season on 20 trees growing in a commercial orchard at Ayr, north Queensland. Whole tree canopy leaf fruit ratios were either decreased by pruning vegetatively flushing terminals or increased by thinning flowering panicles. Unfortunately, the leaf:fruit ratios were not significantly (P < 0. 05) altered by these treatments and the only quality characteristic consistently affected was skin red blush colour. In the second leaf:fruit ratio experiment conducted during the 1995196 season, leaf:fruit ratios were altered on individual branches to overcome the high tree-to-tree variability encountered in the first experiment and to more accurately establish specific ratios. Decreasing the leaf:fruit ratio to 30 resulted in smaller fruits with lower dry matter (DM) percentage (generally used as an indicator of fruit maturity), but extended the shelf life by 2 days, increased the Ca concentration in the pulp tissue by 27%, and improved storage performance by reducing external chilling injury (Cl). Increasing the leaf:fruit ratio to 60 produced larger fruits and extended shelf life by approximately 2 days, but had no effect on DM percentage or pulp Ca concentration………