Abstract

The International Rice Research Institute (IRRI) has developed a new plant type (NPT) and F_t hybrids to further increase rice yield potential. In this study we compared yield and yield-related traits among four genotypic groups : indica inbreds, F[ hybrids, NPT and NPT X indica lines; and determined the contribution of biomass partitioning and translocation to grain yield under sub-optimum growing conditions. Field experiments were conduct¬ed in 1998 wet season (WS) and 1999 dry seasons (DS) in the Philippines. Forty-seven genotypes in the WS and 46 genotypes in the DS were studied. Growth analyses were done at flowering and physiological maturity and yield, and yield components were measured at physiological maturity. Among the genotypic groups, average grain yield of the Fj hybrids was the highest and that of the NPT lines was the lowest. Grain yield was highly associated with harvest index (HI) with an r² of 0.73-0.84 in both seasons. The relationship between grain yield and biomass production was relatively weak. A negative relationship was observed between T,the amount of biomass accumulated before flowering and translocated to the grains during grain filling and W_r the biomass accumulation from flowering to physiological maturity. The NPT lines had the highest average W_rbut had the lowest Tamong the genotypic groups, which was opposite of that of the Fj hybrids. Compared to W_r, Twas more closely related to HI and grain yield. Results suggest that under sub-optimum growing conditions such as low total solar radiation increasing Tand HI is vital for achieving high actual grain yield in irrigated rice