Objective The study aims to analyze the dynamic changes of panicles per plant, leaf area index (LAI), leaf SPAD, and light transmittance rate (LTR) in late-season indica hybrid rice, further clarify their interrelationships and their effects on yield and yield-related traits, and provide a theoretical guidance for hybrid rice breeding and production practice.
Method Five three-line sterile lines and six restorer lines, which are widely used in South China, were used as hybrid combination parents, and a random block experiment of 27 hybrid combinations was conducted in Guangzhou in the late season of 2021. The dynamic changes of photosynthetic parameters, the effects of photosynthetic parameters at different growth and development stages on yield and yield-related traits, and their dynamic correlation were studied.
Result The number of hybrid tillers increased linearly after transplantation, peaked on 25 d after transplantation, and entered a stable period at the initial heading stage (60 d after transplanting). The hybrid LAI rapidly increased after transplanting, reaching its highest value at the late stage of spike differentiation (50 d after transplanting), and then entered a decline period. The leaf SPAD of hybrids gradually decreased after transplantation, and there was no significant difference at the early growth and development stage, while there was significant (P < 0.05) or extremely significant (P < 0.01) differences between the SPAD at the grain-filling stage. The LTR of hybrid populations decreased gradually with the development process. The correlation analysis showed that there was a highly significant positive correlation between the number of tillers per plant and hybrid yield at peak tillering stage (10−20 d after transplanting), initial heading stage (60 d after transplanting), and grain-filling stage (76 d after transplanting). The yield increase effect was mainly achieved by increasing the number of filled grains per plant. The excessive number of tillers during peak tillering stage to the late stage of spike differentiation (25−50 d after transplanting) increased the ineffective tillers, resulted in a decrease in hybrid seed setting rate and a significant decrease in yield. The hybrid LAI value at tilering stage (20 d after transplanting) and initial heading stage (60 d after transplanting) showed a significant or extremely significant positive correlation with yield, with the correlation coefficients of 0.296 and 0.255, respectively. The yield increase effect were mainly achieved by increasing the number of filled grains per plant and the weight of 1000-grain. The LAI value at grain-filling stage (76 d after transplanting) showed a highly significant negative correlation with yield with the correlation coefficient of −0.312. The SPAD of hybrids at the early stage of growth (15−50 d after transplanting) had a significant or extremely significant increase in yield, while the SPAD value in the later stage (76−90 d after transplanting) caused a very significant decrease in yield. The LTR of hybrid populations showed extremely significant negative correlation with their yield, the correlation coefficients between LTR and yield at tillering stage (20 d after transplanting), and early stage of spike differentiation (38 d after transplanting) were −0.282 and −0.384, respectively.
Conclusion The combinations derived from ‘Tianfeng-A’, ‘Wufeng-A’, ‘R998’ and ‘R308’ have strong early tillering ability, a large number of stem tillers, a large LAI, and good early growth and rapid development. The combinations of ‘Yangtai-A’ and ‘R998’ show a lower LTR in the early growing stage and a higher LTR in the later stage, which is much beneficial for plant photosynthesis and yield improvement. The yield of hybrids is affected by photosynthetic parameters at different stages of growth and development, through influencing the different yield traits. By fitting the regression equation between photosynthetic parameters and hybrid yield, the yield of hybrids can be well predicted at early growing stage.
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