Photosynthesis and radiation use efficiency at anthesis in relation to biomass accumulation and yield in Basmati rice (Oryza sativa L.)

The present study was conducted to evaluate the role of traits associated with photosynthesis, Radiation interception (RI) and Radiation Use Efficiency (RUE) in relation to biomass and yield in Basmati rice genotypes. It was hypothesized that, whether yield improvement of Basmati rice will depend on enhancing the biomass through better RI and RUE or harvest index or both. A field experiment was conducted with nineteen aromatic rice genotypes, which included eighteen Basmati and one aromatic hybrid (PRH-10). Among the nineteen genotypes there was variability in biomass production and leaf area and the biomass production was linearly correlated with total intercepted PAR (TIPAR) between 55 and 95 DAS. Higher radiation interception was associated with the variability in crop growth rate among the genotypes. There was a high variability in the RUE ranging from (1.46-2.89 g MJ(-1)), and those genotypes maintained higher crop growth rate (CGR). Genotypes with higher LAI were associated with a lower extinction coefficient (k) and improved RUE. However, the leaf photosynthetic parameters viz. photosynthesis rate, transpiration rate and stomatal conductance were negatively associated with the aboveground biomass at anthesis. The net assimilation rate (NAR) was positively correlated with the photosynthetic parameters. Comparison of the mean of five highest biomass Basmati genotypes (HBBG), namely PB 1121, Sarbati, Pant Basmati-1, PB 1728 and PB1718 was done with the aromatic rice hybrid PRH-10. At anthesis stage, there was not much difference in dry weight, CGR and in RUE in HBBG compared to PRH-10. At harvest, the HBBG showed higher biomass (+ 15%) compared to PRH-10. However, the grain yield was higher in PRH-10 (+ 8%) due to its higher harvest index (+ 25%) over HBBGs. It was associated with higher number of spikelets per panicle (+ 19.5%) and % filled spikelets (+ 7.5%). Moreover, less height in PRH-10 compared to HBBG also favoured higher harvest index. The better yield performance of PRH-10 could be associated with photosynthetic parameters-higher flag leaf area (+ 40%) and higher flag leaf photosynthesis (+ 48%). It may have contributed in supporting the higher sink demand leading to high yield in PRH-10. Therefore, it can be concluded from the present study that high biomass Basmati genotypes which have high RUE in combination with higher sink capacity (i.e., number of spikelets/panicles) and better partitioning due to reduced height can lead to yield enhancement in Basmati rice.