Competition regulates mango fruiting above a floral density threshold

Abstract

Mango flowering is interannually variable and temperature dependent. Flowering intensity declines with increasing pre-flowering temperatures associated with global warming, potentially limiting yields. Additionally, floral density that does not contribute to greater yield represents an unnecessary drain on plant resources such as nutrients, water, and carbohydrates. This can lead to reduced fruit bearing capacity in later stages of cropping or contribute to interannual yield variation. The objective of this work was to identify the floral density compensation point (FDCP), above which additional flowering becomes redundant, and below which surplus carbohydrates are partitioned to existing flowers, fruit, vegetative growth, or stored. Over two growing seasons, the number of inflorescences on 32 Calypso® mango trees in Dimbulah, Australia were thinned by up to 95%, resulting in floral densities between 0.09 and 4.14 inflorescences per trunk cross sectional area (cm2). Fruit yield, number, composition, vegetative growth, and starch concentration in terminal growth units were measured for each of the trees. Calypso® mango trees have excess floral density, beyond the maximum fruit biomass the tree can support to harvest. Below the FDCP, the tree is unable to compensate for low numbers of inflorescences, and floral density was strongly positively correlated with fruit number and yield, and strongly negatively correlated with fruit per panicle and total soluble solids concentration of ripe fruit. Above the FDCP fruit yield, number and total soluble solids concentration were only weakly related to floral density as they appear limited by carbohydrate availability rather than flowering. Fruit weight, vegetative regrowth of fruiting and non-fruiting terminals, and the starch concentration in terminal growth units were less dependent upon the FDCP and changed continuously across the floral densities evaluated. This information will be valuable for managing mango flowering under current and future climates.