Objective Whether the litchi trees form flowers is a key determinant of litchi yield. In 2024, in the litchiproducing areas of Guangdong Province, phenomena such as poor flower quality, reduced flowers or even complete absence of blossoms occurred in mid-late maturing litchi, resulting in an extremely low-yield year for litchi, marking a "super off-year" for lychee production. Exploring the influence and restriction of climate condition on the floral initiation of mid-late maturing litchi can furnish a scientific basis for effectively circumventing risks in litchi production, thereby promoting the sustainable development of litchi industry within the context of a complex and changeable climate environment.

Method The daily observation data from six national meteorological stations in Guangdong Province from November 2023 to February 2024 and the data on the floral formation rate of litchi were used in this study. The climate conditions during the flower differentiation period of mid-late maturing litchi in six typical regions in the litchi-producing areas of Guangdong Province, namely, Lianjiang and Gaozhou in western Guangdong, Zengcheng and Dongguan in the Pearl River Delta, and Huilai and Raoping in eastern Guangdong, were analyzed from three aspects: temperature, sunlight, and moisture. The relationship between the differences in the floral formation rate of litchi and the climate conditions was compared and analyzed.

Result During the critical period for the floral formation of mid-late maturing litchi in the litchi-producing areas of Guangdong Province, there were situations such as relatively high temperatures with large variability, late occurrence of low temperatures and long intervals between them, excessive accumulated heat, less sunlight with prominent periods of low light intensity, and insufficient precipitation in the later stage of floral formation, which led to few or no flowers on litchi. There was generally little difference in moisture conditions, but significant differences in temperature and sunlight conditions in the six typical regions, indicating that temperature and sunlight conditions had a greater restrictive effect on the few or no flowers of mid-late maturing litchi in Guangdong Province in 2024 compared with moisture conditions. The traditional high-quality mid-late maturing litchi varieties such as 'Guiwei' and 'Nuomici' in Raoping had a floral formation rate of over 70%, while it was less than 20% in the other regions. This was related to the relatively good climate conditions in Raoping. The specific indicators were as follows: the maximum number of days with an average daily temperature below 19.0℃ was 92 days, the second highest number of days with an average daily temperature below 14.0℃ was 30 days, the minimum number of days with the maximum daily temperature ≥ 25.0℃ was only 29 days, the extremely low temperature was 3.0-4.0℃ and lasted for no more than 3 days, the amount of heat accumulation at hot day with the minimum daily temperature ≥ 22℃ was only 22.2℃, the sunshine hours were over 20% higher than those in the same period of the past five years and the minimum number of days with a daily cumulative sunshine hours ≤ 2 h was only 13 days, and the precipitation from late December 2023 to late January 2024 was less than 15 mm while the precipitation in early and mid-February 2024 exceeded 15 mm. In the future, the above factors can be considered in the study of the relationship between litchi yield and climate conditions, and the production management of litchi orchards. Under the same climate conditions, the floral formation rate of varieties with high chilling requirements such as 'Guiwei' and 'Nuomici' in Dongguan and Huilai was less than 20%, while that of varieties with lower chilling requirements such as 'Guanyinlvl' and 'Lingfengnuo' reached more than 50%.

Conclusion Temperature and sunlight conditions are the dominant climatic factors that restrict the floral differentiation of mid-late maturing litchi in Guangdong Province. Against the backdrop of global warming, disasters such as warm winters, continuous overcast and rainy conditions with insufficient sunlight should not be overlooked. It is recommended that litchi farmers adjust the planted varieties in a timely manner, thereby promoting the sustainable and high-quality development of the litchi industry.