Heat unit summation - an index for predicting fruit maturity in litchi (Litchi chinensis)

The GDD values were determined using daily maximum and minimum temperatures considering a baseline temperature of 10°C. The maximum GDD (1902.7°C) was received during 1999. Among cultivars, HUS ranged from 1258.6°C (Trikolia) to 1661.6°C (Dehradun). The mean TSS: acid ratio was maximum during 1999 (71.2). Among cultivars TSS: acid ratio ranged from 53.3 (China) to 79.9 (Rose Scented). Regression analysis indicated linear relationship between HUS and TSS: acid ratio in 8 cultivars (R²°0.50), viz. Ajhauli, Green, China, Deshi, Dehradun, Kasba, Dehra Rose and Shahi. Based on values of GDD and TSS: acid ratio, the cultivars have been classified into different groups, viz., GDD < 1400°C (8 cultivars), 1400–1600°C (3)°1600°C (2), TSS: acid ratio < 60 (3) and 60–70 (5)°70 (5).