Stress tolerance indices for the identification of low phosphorus tolerant introgression lines derived from Oryza rufipogon Griff

Soil phosphorus (P) deficiency is one of the major challenges for the cultivation of rice worldwide because it limits the growth and productivity of the crop. Therefore, the ability to grow in P-deficit soils is an important trait for rice cultivation. O . rufipogon Griff., a wild relative of rice, is a source of genetic variation for low phosphorus tolerance. The present study was undertaken to identify low P stress-tolerant introgression lines by analysing stress tolerance indices of 40 introgression lines of O. rufipogon. The populations were screened under low soil P and normal soil P plots for two growing seasons. Based on yield under stress and normal conditions, we computed different stress indices, including stress tolerance index (STI), tolerance index, yield reduction ratio (YR), stress susceptibility index, yield stability index (YSI), yield index, per cent yield reduction and geometric mean productivity (GMP). The studies of correlation analysis, principal component analysis and clustering revealed that STI, YSI and GMP were ideal indices for the selection of genotypes that performed well under both stress and normal conditions. Based on these indices, introgression lines (IL-24, IL-29 and IL-32) were identified as promising low P tolerant lines, which exhibited better grain yield under both stress (Y S ) and normal (Y P ) conditions. These pre-breeding lines serve as valuable genetic resources for low P tolerance in rice breeding programmes across the world.