Analysis of the biomass productivity of super high-yielding rice cultivar 'Hokuriku 193' in terms of the light source utilization

To feed the growing world population, the enhancement of rice yield per unit area is one of the most important goals for crop science. Understanding the physiological factors underlying the high-yielding cultivars is important to accelerate the improvement of yield potential of rice. 'Hokuriku 193' (H193), recently bred in Japan, showed the highest yield record in Japan (Okamura et al., 2021), and is known as the super high-yielding cultivar. The high yield of H193 is explained by both biomass productivity and sink capacity. (Yoshinaga et al., 2013). However, the physiological basis of the greater biomass productivity has yet to be elucidated. In the present study, we aimed to determine the factors contributing to the greater biomass production of H193. The field experiment was conducted at the paddy field of Kyoto University and Tokyo University of Agriculture and Technology in Japan in 2022. Four rice cultivars; H193, 'Takanari', 'Tachisugata', and 'Nipponbare' were planted at 22.2 plants m -2 and one plant per hill. The fertilizer of 4 g N m -2 , 3.1 g P m -2 , and 3.7 g K m -2 was applied as basal, and 2 g N m -2 , 1.6 g P m -2 , and 1.9 g K m -2 was applied at the panicle initiation stage, respectively. Rough grain yield (RGY), total dry weight (TDW), leaf area index(LAI), and fraction of intercepted photosynthetically active radiation (fIPAR) of each cultivar were measured from the tillering stage to the maturity stage (4~5 times). Across two locations, H193 showed greater RGY at harvest and TDW after the panicle initiation stage than that of other cultivars. The fIPAR of H193 also tended to be greater than other cultivars, whereas the radiation use efficiency (RUE) of H193 was almost the same as other cultivars. There was also no difference in LAI among cultivars until the panicle initiation stage. Hence, the greater TDW of H193 was attributable to its greater fIPAR, but the LAI is not the factor explaining the variation of fIPAR. Therefore, canopy architecture may be the reason for the difference in fIPAR. Further characterization of the canopy architecture of H193 is mentioned in the presentation.