In-Orchard Sizing of Mango Fruit: 3. Allometry and Growth Model

The forecast of fruit weight at harvest requires (i) a non-destructive method for assessment of weight (Fw) of fruit-on-tree and (ii) the knowledge of fruit growth dynamics. To address the first issue for mango fruit, several allometric relationships between Fw and fruit-lineal dimensions of length (L), width (W), and thickness (T) were considered, with the relationship Fw=kLWT recommended. A k value of 0.5146 was established for fruit of the cultivar Honey Gold for fruit past the stone-hardening stage, based on assessment of 1091 fruit from 13 season/orchard populations and preliminary values of 0.5376, 0.5151, and 0.5239 for the Keitt, Kensington Pride, and R2E2, respectively, on the basis of more limited datasets. A combined cultivar model was recommended across all cultivars considered, except Keitt. The variation in k between populations of Keitt and Honey Gold fruit was due to the difference in fruit density, rather than shape. This conclusion should be tested in context of other cultivars and fruit development. A correction for developmental age was established for Honey Gold fruit, viz., kcorr=−0.0009× DAFB+0.5975 for fruit up to ~1224 growing degree days. The need for similar corrections for other cultivars should be investigated. For the second issue, the use of a linear function based on measurements of Fw in the weeks immediately before harvest was recommended for forecasting harvest-time weight to an accuracy of approximately 10%. A Logistic function described Fw increase better than a Gompertz function; however, a change in growing conditions during fruit development limits the reliability of such models for forecasting fruit weight at harvest maturity. Rather, it is proposed that a set of reference models based on a set of reference Logistic model parameters for a suite of growing conditions be developed for use in guiding agronomic interventions earlier in fruit development to maintain growth on a trajectory to achieve a desired weight at harvest.