Dry spells trigger durian flowering in aseasonal tropics.

The flowering period of durian is influenced by weather conditions such as prolonged drought and low temperatures. However, the specific criteria and durations of these conditions remain unclear. This study aimed to identify weather conditions that trigger durian flowering by monitoring its phenology and analyzing the relationship between minimum temperature and rainfall using two types of durian- grafting type and seed-grown type. Three flowering events were observed in 2022 and two in 2023. Considering there were no differences in the number or timing of flowering events among the two types, it suggests that genetic background differences do not influence flowering phenology. All flowering events were best explained using the 15-day moving average of rainfall, with the peak of the first flowering occurring approximately 50 days after the 15-day moving average of rainfall fell below 1 mm. These results suggest that drought accumulation over approximately 15 days may trigger the induction of durian flower buds. However, no correlation was determined between the minimum temperature and the first flowering date. These findings indicate that durian flowering is induced by milder drought conditions than those previously proposed. Differences in variety and climate may have led to results different from those reported in earlier studies. Long-term monitoring across multiple sites and varieties is required to discuss these differences further.