Modelling kiwifruit growth: impact of pollination period on fruit growth dynamic

C. Pinto, V. Tudela, G. Reginato
The profitability of kiwifruit orchards is directly related to yield and fruit size. Accurate estimates of crop load and mean fruit weight are required by growers and exporters as early in the growing season as possible. Optimal kiwifruit production is highly dependent on pollination because fruit size is closely related to the number of seeds per fruit. Kiwifruit has a highly efficient reproductive system, but seed number could be limited by the effective pollination period (EPP) and therefore affect the size of the fruit. The objective of this study was to determine the impact of effective pollination period on kiwifruit size at harvest and on the dynamic of fruit growth. The trial was carried out in two 'Hayward' orchards in the Central Valley of Chile. Hand pollination was performed with pollen of male vines from the same orchard, collected 1 day before anthesis of each treatment. Female flowers were isolated by bagging them before anthesis to avoid free pollination. Isolated flowers were hand-pollinated at 1, 2, 3, 4, 5, 6, and 7 days after anthesis. After that, starting 23 days after pollination, the fruits were evaluated by their length and equatorial diameter (maximum and minimum) every week with a digital caliper. Fruit quality parameters were evaluated at harvest. Segmented nonlinear regressions were used to describe the growth along the season, as a function of growing degree days (GDD) accumulation, allowing to compare the time of pollination and location (orchard). Preliminary results indicated that kiwifruit growth can be described by a segmented nonlinear regression of two phases. The initial phase, from flowering to 430 GDD showed higher rates of length and equatorial diameter increase. In contrast, the final phase, since 430 GDD up to harvest, showed a linear fruit growth, but with a slower rate of length and diameter increase, and similar changes on both fruit measures. In both phases, the growth rate and fruit size at harvest were unaffected by EPP.
Pinto, C., Tudela, V. and Reginato, G. (2022). Modelling kiwifruit growth: impact of pollination period on fruit growth dynamic. Acta Hortic. 1332, 245-252
DOI: 10.17660/ActaHortic.2022.1332.33
Actinidia, fruit size, growing degree days (GDD), thermal time, seed number

Acta Horticulturae