Application of stress indices for low temperature and deep sowing stress screening of rice genotypes

Low temperature or cold stress and deep sowing plays a pivotal role in limiting rice (Oryza sativa L.) productivity in the temperate rice growing regions as well as in tropical high lands worldwide. A better understanding of stress tolerance mechanism in rice plants will help to develop rice germplasm with improved field level tolerance under variable temperature and sowing deep conditions. Using previously developed stress indices, this study presents results from low temperature and deep sowing screening of four rice genotypes. A group of 25 seeds per replicate (total of 3 replicates) was subjected to stress by deep sowing (15 cm) while another group was subjected to cold stress (13 degrees C-10 h/18 degrees C-14 h) and the control group remained under optimum conditions (25 degrees C and sowing depth of 1.5 cm). The Geometric Mean (GM), Stress Tolerance Index (STI) and Stress Susceptibility Index (SSI) were used to evaluate the genotypic performance under control and stress conditions. The results indicate that it was possible to identify superior genotypes for tolerance based on their stress indices. The indices although correlated, were found to be effective for the selection of genotypes with good yield potential under control and stress treatments and can now be used for genotypic screening under field conditions.