关键词: 二季晚稻, 安全齐穗, 低温, 结实率, 产量

Abstract:

【Objective】 The objective of this study is to determine the critical lowest temperature for the safe heading of various types of late-season rice cultivars and the dates for their safe full heading in different double-season rice production regions of Hubei Province, and to provide guidelines for the rational layout and scientific arrangement of double-season rice production in different regions. 【Method】 Different types of late-season rice cultivars including japonica, indica and indica-japonica hybrid those are suitable for different cropping methods in the double-season rice cropping regions of Hubei Province were used as materials and a multi-site field experiment with various sowing dates was conducted at Chibi City, Xianning, Gongan County, Jingzhou, Hongshan District, Wuhan, Tuanfeng County, Huanggang, and Xiaochang County, Xiaogan, Hubei Province, respectively, in 2020 and 2021. Meanwhile, simulated low-temperature treatment was imposed to the potted plants during booting and heading in a pot experiment. The grain-setting rate and grain yield per plant or hill were investigated and the relationship between grain-setting rate and air temperature prior to full heading was analyzed. The critical lowest temperature for their safe heading of various types of cultivars was determined using the temperature under that the grain-setting rate was reduced to 82% of that under the optimum temperature. Furthermore, the daily risk maps for the full heading of different cultivar types in September were drawn based on the meteorological data in the past 30 years in various double-season rice cropping regions of Hubei Province. The latest safe dates for full heading of various types of cultivars in different double-season rice cropping regions were determined as the injury from low temperature to their heading can be avoided in more than 80% of years. 【Result】 With the delay of sowing date, the heading date of various cultivars was delayed. The grain yield per plant or hill decreased significantly under late sowing conditions. Grain-setting rate, a determinant factor that affects the yield of individual plant or hill, was quadratically related to the mean daily temperature in the 4 days prior to full heading. The critical lowest temperature for the safe heading in the 4 days prior to full heading was 19.6 ℃ for japonica cultivars, which was 0.4 ℃ lower than the conventional standard; and 22.4 ℃ for indica cultivars, which was 0.4 ℃ higher than the conventional standard; and 22.2 ℃ for indica-japonica hybrid cultivars, which was close to that of indica cultivars. The latest safe date for the full heading of late-season japonica, indica and indica-japonica hybrid cultivars was September 25-28, 16-19 and 17-20 in southeastern Hubei; September 23-27, 13-19 and 14-20 in eastern Hubei; September 25-27, 10-17 and 10-18 in Jianghan Plain; September 22-26, 7-15 and 7-17 in northern Hubei, respectively. 【Conclusion】 The safe date of full heading for late-season rice differed much among various cultivar types and in different double-season rice cropping regions of Hubei Province. It showed a trend that became earlier from south to north in Hubei Province, and was earlier for indica cultivars than for japonica cultivars. The latest safe date of full heading for indica-japonica hybrid cultivars was close to that for indica cultivars. It is of importance to select suitable cultivars and arrange reasonable sowing dates according to the local climatic conditions and cultivar characteristics for the safe production of late-season rice. Plantation using japonica cultivars is helpful to combat the damage from low temperature during heading and flowering in the late-season rice production.

Key words: late-season rice, safe heading, low temperature, grain-setting rate, grain yield