A PREDICTION OF DEVELOPMENTAL STAGES IN POTATO PLANTS BASED ON THE ACCUMULATION OF HEAT UNITS

Growth of potato plants (cv. Desiree) was analyzed over a seven-year p eriod in commercial fields at two locations, during Israel's two growi ng seasons. The effect of temperature on developmental rate was studie d to determine the appropriate heat-unit model for predicting dates of tuber appearance, and termination of the yield-bulking period The bes t prediction of tuber appearance date was based on the accumulation of heat units calculated using a linear relationship between development al rate and daily mean temperature with a combination of 2-degrees-C-2 5-degrees-C-35-degrees-C for threshold, optimum and maximum temperatur es, respectively. Predictions of bulking cessation based on several re ported models were not any more accurate than predictions based on the accumulation of chronological days. High temperatures were found to n egatively affect the developmental rate at both developmental stages. However our analyses indicate that the maximum temperature for tuber a ppearance is higher than that reported previously.