PREDICTING HARVEST DATE FOR KIWIFRUIT - VARIATION OF SOLUBLE SOLIDS CONCENTRATION WITH MEAN TEMPERATURE

The increase in soluble solids concentration (SSC) of kiwifruit (Actin idia deliciosa cv. Hayward) maturing on the vine was monitored in 35 o rchards in eight regions of New Zealand during 1981 and in 37 orchards during 1982. During these 2 years the date of commercial maturity (SS C of 6.2%) ranged from 16 April at Nelson to 25 May at Kerikeri, a spr ead of 39 days. It tended to be earliest at the southern-most and henc e coolest sites. A simple model that has been used by others to predic t the date of commercial maturity was tested. This model relates the t ime taken for fruit to increase in SSC from 5.0 to 6.5% to the mean ai r temperature during that period. Our data confirmed that the rate of increase in SSC increased as the mean temperature decreased from 15 to 11-degrees-C. However, the predictive model was not consistent betwee n or within seasons. There is some evidence that this lack of consiste ncy is caused, at least in part, by factors other than temperature inf luencing the rate of SSC increase. The rate of increase in SSC was inv ersely correlated with the date that fruit in the orchard reached a SS C of 5.0%. This suggests that the state of vine development influences the rate of maturation. It is also possible that the description of t emperature was inappropriate, either in the use of mean temperatures, or because air temperatures recorded at standard meteorological sites did not adequately represent the temperature of the fruit.