Thermal unit requirement of grape (Vitis vinifera L.) varieties under south western Punjab conditions

Abstract

Weather components have significant impact on the phenology of fruit plants. In order to study the effect of heat, photothermal and heliothermal units on phenology of grapes, an experiment was conducted during 2016 and 2017 on eleven grape varieties. The weather based indices were used for characterizing the thermal response to various phenophases of different grape varieties. Based on the thermal response the eleven varieties were classified into early, mid and late maturing categories. The fruit ripening was differed by 7-9 days for early, 4-8 days for mid and 1-3 days for late ripening groups. For early, mid and late maturing varieties the accumulated range of growing degree days was 1303-1530, 1617-1712 and 1912-1959 °C day, photothermal unit was 15971-19032, 20201-21484 and 24255-24923°C day. Likewise, minimum heliothermal unit was required by early ripening varieties i.e., Himrod(9973 °C days) and Madeliene Anguvine (11235 °C days) but, maximum for long duration varieties like Black Muscat (15000 days) and Angur Early (14579 °C days). Maximum and minimum heat use efficiency was recorded by variety Perlette (1.57) and Black Muscat (0.96), respectively.