Phenological and yield responses for the identification of both vegetative and reproductive stages drought-tolerant rice genotypes for future breeding

Rice production is severely threatened by drought stress. To develop drought-tolerant varieties, the selection of donors for the breeding programme is crucial. Twenty-one rice genotypes were evaluated at the vegetative and reproductive stages under drought. Higher relative water content (> 65%) and leaf water potential (> - 3.50 MPa) in Danteshwari, Mahamaya, Samleshwari, Poornima, IBD-1, Safri 17, Sahabhagidhan, Vandana and N22 explained their drought tolerance with higher biomass production, lower drought score and early stress recovery rate of 1 and 3 under vegetative stage drought. At the reproductive stage drought, higher grain yield and less relative yield reduction was found in Mahamaya (2.42 t/ha, 46.37%), Samleshwari (2.05 t/ha, 42.88%), Poornima (1.86 t/ha, 42.67%), Sahabhagidhan (2 t/ha, 57.72%) and Danteshwari (2 t/ha, 39.11%), showed higher tolerance due to greater leaf water potential and biomass with a lower reduction in grain filling percentage due to more remobilization of assimilates to the grains. Though, N22 and Anjali flowered 5-7 days earlier in drought stress compared to well-watered condition, partially responsible for increased grain filling under drought. Therefore, visual selection for a large sink size under favorable conditions and higher biomass accumulation under vegetative drought stress with greater fertility under reproduction stage is favorable for maintaining higher grain yield in rice. Further, higher expression of OsAP37, EDT1, OsLEA3-1, OsDIL, OsDRAP1, OsNAC14, OsNAR2.1, OsWRKY30 and OsRab7 in Mahamaya, Samleshwari, Poornima, Sahabhagidhan, and Danteshwari supported the higher grain yield under drought stress.