Radiation use efficiency and its classification of main varieties in double-cropping rice region of South China

Radiation use efficiency (RUE) of rice varieties is an important factor influencing grain yields of double-cropping rice in South China. However, there have been few studies of rice RUE and its relationship to agronomic traits. We conducted two-season field experiments to evaluate the RUE of 36 major rice varieties in a double-cropping rice region of South China. The relationships between RUE and the main agronomic traits (for example, yield) were explored, and the clustering analysis of tested varieties were classified. The findings revealed highly significant difference of RUE existed in different rice varieties and cropping seasons, respectively. In early and late seasons, RUEs were significantly and positively correlated with the grain yield, the harvest index, and the 1000-grain weight. In the early season, RUE was significantly positively correlated with the biomass and significantly negatively correlated with the growth period; however, in the late season, these correlations were not significant. Principal component analysis revealed the 12 agronomic traits of the tested varieties to be compressed to four independent comprehensive indexes, including the yield and light energy efficiency factor, the panicle and grain number factor, the growth period and grain weight factor, and the seed setting rate factor, in the early season; and to five independent comprehensive indexes, including the yield and light energy efficiency factor, the panicle and grain number factor, the biomass factor, the growth period and grain weight factor, and the seed setting rate factor, in the late season. Clustering analysis revealed that the varieties tested in this study could be divided into three groups:low RUE, medium RUE, and high RUE. Rice varieties numbers with low RUE, medium RUE, and high RUE accounted for 50.0%, 38.9%, and 11.1%, respectively, of the total numbers of tested varieties in the early season and for 27.8%, 47.2%, and 25.0%, respectively of the total numbers in the late season. 'Yliangyou 143' 'Teyou 524' 'Tianyou3301' and 'Teyou3301' were identified as high-RUE varieties in the early season, and 'Wuyou308' 'Tianyou3618' 'Wuyou163' 'Wuyou376' 'Tianyou998' 'Tianyouhuazhan' 'Tianyou3301' 'guang8you188' and 'Yliang you 305' were identified as high-RUE varieties in the late season in South China. In our study, the classification of RUE types for rice varieties has been reported for the first time. The findings will have important guiding significance for the variety layout in growing areas and both the breeding of high-RUE varieties and their efficient utilization.