Genetic Analysis of Seedling Vigor in Temperate japonica Rice (Oryza sativa L.).

Seedling vigor is an important trait for direct seeded rice (DSR) cultivation. In California, germinated rice seeds are seeded aerially onto flooded fields. Released varieties have very similar vigor under these conditions. M-203 and M-206 are medium grain temperate japonica varieties adapted for the California production environment. Evaluation of these two varieties under direct seeding into soil revealed that M-203 exhibits better vigor than M-206 under controlled conditions (12-hr photoperiod, constant 28°C) as well as in the greenhouse and outdoor basins. A recombinant inbred line (RIL) population (F₇; n = 178) developed from the cross M-203/M-206 was evaluated for seedling height 7 and 14 days after sowing (PH7 and PH14), growth rate (GR) and fresh weight of the aboveground biomass (FW). Additionally the RIL population was evaluated under cold stress (13°C) and alternate temperature conditions (28°C/13°C) in a controlled environment. M-203 presented significantly better vigor than M-206 during the early stage of seedling growth (PH7) across all environments. Transgressive segregation was observed for all traits. Six RILs were identified as consistently exhibiting greater vigor than M-203 considering all traits measured in all growing environments. Preliminary genotyping was performed using 24 single nucleotide polymorphism (SNP) markers. The RIL population is currently being genotyped using a reduced representation sequencing approach and the resulting marker data will be used with the trait data to identify QTLs contributing to the difference in seedling vigor exhibited by M-203 and M-206.