Developing a Screening Protocol for Drought Tolerance Classification of 100 Elite Rice Lines.

Drought stress is a major abiotic stress factor that affects growth and development of plants at all stages. Developing a screening protocol to identify variability for drought stress tolerance during seedling establishment is key to identifying stress tolerant lines for early-season vigor breeding. An experiment was conducted to evaluate 100 rice experimental breeding lines for tolerance to drought stress under pot-culture conditions under a mini-greenhouse environment. The rice seedlings were subjected to two different soil moisture regimes, 100 and 50% field capacity, from 10 to 30 days after sowing (DAS). Several morpho-physiological parameters including root traits were measured at the end of the experiment, 25-30 DAS. Significant soil moisture stress by cultivar interactions were observed for most of the parameters measured. A cumulative drought response index (CDRI) was developed by summing the individual response indices of all the parameters. The CDRI values varied between 14.7 and 27.9 among the rice lines tested. Based on CDRI and standard deviation values, five and 28, 45, and 16 lines were identified as the most sensitive, sensitive, moderately sensitive, and moderately tolerant, most tolerant to drought stress, respectively. The rice variety Cheniere and breeding line RU1402174, were identified as the least and the most tolerant to drought among the 100 rice genotypes tested. Even though significant linear correlations were obtained between CDRI and root (R² = 0.91) and shoot (R² = 0.48) parameters, root traits were important in identifying drought tolerant lines during the seedling establishment stages in rice. The identified rice lines will be a valuable resource for rice breeders to develop new genotypes best suited for drought stress conditions. However, further studies are needed to test these lines at different growth stages under stress and field conditions to identify the stability of these tolerant lines for drought.