Comparison of yield potential among indica inbred, hybrid, and first-, and second- generation new plant type (NPT) rices

Various approaches are being undertaken to increase the yield potential of rice at the International Rice Research Institute [Los Banos, Laguna, Philippines]. Among the more prominent ones is the exploitation of heterosis by breeding tropical hybrid rice and the development of second-generation new plant type (NPT), which is the cross of the first-generation NPT with indica lines. This experiment evaluated some materials from these approaches last year. Fifteen genotypes: one indica inbred, five hybrids, one first-generation NPT, and eight second-generation NPT lines were planted in the IRRI Farm during the dry and wet seasons of 2002. A total of 200 kg N/ha was applied during the dry season; 70 kg was used in the wet season. Plant samples from a 0.5 sq m area were taken during mid-tillering stage, panicle initiation, flowering, and at physiological maturity for growth and yield component analyses. A 5 sq m area was harvested from each plot for yield measurement. The hybrids had the highest average yield among the four groups. The yield advantage of the hybrids over the inbred IR72 was 24% during the dry season and 18% during the wet season. IR73868H gave the highest yield among the hybrids in both seasons. The second-generation NPT lines had the next highest average but was only 4% higher than IR72. The NPT line IR68552-100-1-2-2 had the lowest yield because of its very low number of spikelets per unit area and harvest index although it had the highest total dry matter per sq m. The reason for the highest yield of the hybrids is the fact that they had the highest number of spikelets per unit area and highest harvest index than the other groups. This also explains why the second-generation NPT lines have higher yield than the first-generation NPT lines. It is expected that the second-generation NPT developed by crossing tropical japonica NPT lines with elite indica parents will have higher yield potential