Improving the prediction of processing bean maturity based on the growing-degree day approach

Four snap bean (Phaseolus vulgaris L.) cultivars, Goldrush, Teseo, Labrador , and Flevoro, were grown in irrigated fields of southern Quebec between 19 85 and 1998. Data on phenology collected from these fields were used to det ermine which base temperature would best predict time from sowing to maturi ty. The optimal base temperature was 0 degreesC for 'Goldrush', 'Teseo', an d 'Labrador' and 6.7 degreesC for 'Flevoro'. Adjusting different base tempe ratures for intermediate developmental stages (emergence, flowering) did no t improve the prediction model. All years for a given cultivar were then us ed to determine the base temperature with the lowest coefficient of variati on (CV) for predicting the time from sowing to maturity. A common base temp erature of 0 degreesC was selected for all cultivars, since 'Flevoro' was n ot very sensitive to changes in base temperature. This method improved the prediction of maturity compared with the conventional computation growing-d egree days (GDD) with a base of 10 degreesC. For the years and cultivars us ed in this study, calculating GDD with a base of 0 degreesC gave an overall prediction of maturity of 1.7, 1.5, 2.0, and 1.4 days based on average abs olute differences, for 'Flevoro', 'Goldrush', 'Teseo', and 'Labrador', resp ectively.