Screening of Indica and Japonica Rice Subspecies for Grain Yield and Quality Under High Nighttime Temperature.

We report here on the analysis of a random subset of rice genotypes of indica and japonica subspecies, treated with high nighttime temperature (HNT) stress during flowering, to compare the natural variation between the rice subspecies for HNT tolerance quantified by grain yield and quality. The genotypes were screened in temperaturecontrolled greenhouses for HNT initiated at the R2 and R5 reproductive stages and continued until physiological maturity. A set of 10 indica and 10 japonica diverse rice genotypes were randomly selected from the USDA rice mini-core (URMC) collection. Phenotypic analysis of the genotypes showed that the japonica genotypes had a higher percentage of filled grains per panicle (yield component) when treated with HNT at the R2 and R5 growth stages, and a lower percentage of chalkiness in rice brown grains at the R5 growth stage under HNT compared to indica. We conclude that in this pilot study, the japonica subspecies lines used exhibited more HNT tolerance than the indica subspecies lines in terms of grain yield and quality and represents an important genepool to dissect the genetic mechanisms/pathways involved in the HNT tolerance traits. The identification of genetic markers for grain yield and quality under HNT, would be useful for rice breeders to develop improved U.S. rice cultivars stable for HNT. [ABSTRACT FROM AUTHOR]