Modelling flower production of kiwifruit (Actinidia deliciosa) from winter chilling

Abstract

In warm areas of New Zealand the productivity of kiwifruit vines (Actinidia deliciosa) can be limited by the low number of flowers produced following a warm winter. Our objective was to formulate a model that quantifies how temperatures, use of hydrogen cyanamide (HC), and orchard location affect flower production of kiwifruit vines. Flowering of kiwifruit vines, and winter temperatures, were monitored in a range of climates in New Zealand for 6 years. Mean winter temperatures for the period May‐July ranged from 7.6 to 14.1°C. Over this range the average number of king flowers per winter bud decreased from 2.4 to 0.2 as the temperature increased. Although spraying vines with HC increased the number of king flowers, flower production on treated vines still decreased as the winter temperature increased, in a similar manner to control vines. The number of flowers per winter bud could be modelled using factors for usage of HC, long‐term mean annual temperature, and mean winter temperature (r2 = 0.87). On vines that had not been sprayed with HC, the number of king flowers per winter bud increased by 0.45 for every 1°C decrease in mean winter temperature.