Calcium accumulation in fruit of kiwifruit grown under different windspeed conditions

Many physiological disorders of fruit are associated with low fruit calcium status. This is true for kiwifruit in which fruit storage quality is closely related to fruit calcium concentration. It is well known that calcium transport to a fruit is exclusively via the xylem - calcium is not phloem mobile. Therefore, a fruit’s calcium status will depend on the cumulative inflow of xylem sap through the stalk; this will depend on fruit transpiration, and on the microenvironment in which the fruit develops. A plausible hypothesis says that if the windspeed around a developing fruit is increased, fruit transpiration will be increased, and likewise the accumulation of fruit calcium. To test this hypothesis, trials were conducted, on 10-year-old kiwifruit vines (Actinidia deliciosa 'Hayward') growing in Palmerston North, New Zealand. At fruit set, 12 small electric fans were mounted in the canopy to modify the wind environment of the immediately adjacent fruit. The fans were in operation continuously (24 h /day for several months) from fruit set through to harvest and the wind speed experienced by individual tagged fruit was measured periodically using a small vane anemometer. At harvest the calcium contents of ventilated and control fruits were analysed. The results show that increased windiness is associated with marked increases in fruit calcium.