Effect of two alleles of Tiller Angle Control 1 on grain yield and dry matter production in rice

Improving rice plant architecture is a promising strategy for increasing yield to meet the rising demand for rice production. The effects of modifying tiller angle, a component of plant architecture, on grain yield and dry matter production are poorly understood in rice. The objective of this study was to investigate the effects of two different alleles of TAC1, a major gene responsible for tiller angle, on rice grain yield and dry matter production. A near-isogenic line (NIL) in the genetic background of IR64, a standard indica rice cultivar, containing a genomic segment of chromosome 9 with the japonica TAC1 allele (tac1) from Koshihikari, a standard japonica cultivar, and a reciprocal NIL in the genetic background of Koshihikari with the indica TAC1 allele (TAC1) from IR64 were developed. Field experiments with the NILs and parent cultivars at two different plant densities were conducted over 2 or 3 years. Introgressions of different alleles of TAC1 drastically modified tiller angle regardless of genetic background. However, the introgression of tac1 into IR64 decreased grain yield and dry matter production, whereas the introgression of TAC1 into Koshihikari did not affect these traits regardless of plant density. The effect on light-capture characteristics—plant canopy coverage ratio, fraction of intercepted photosynthetically active radiation, and light extinction coefficient—was greater in the comparison between IR64 and its NIL than in that between Koshihikari and its NIL. No differences in leaf dry weight, leaf area index or leaf nitrogen concentration were found in either comparison. The effects of TAC1 alleles on grain yield and dry matter production via modification of light-capture characteristics differ depending on genetic background. This study demonstrated the complexity of the relationships between canopy structure and canopy photosynthesis, while emphasizing the importance of characterizing three-dimensional canopy structure in crop growth models.