Rice grain quality sinks with submergence

Grain quality is one important trait considered in rice variety development. Abiotic stresses, such as extreme temperature, salinity, and drought, have been reported to affect grain quality. In this study, the authors evaluated the effect of submergence stress in the grain quality of 12 genotypes exposed to complete submergence for 11 days of vegetative stage and compared with those grown in favorable irrigated condition in 2009 dry season. The traits include % brown rice, % milled rice and % head rice, grain size and shape, % chalky grains, % amylose content, alkali spreading value, and % crude protein. The rough rice harvested from submerged genotypes had higher proportion of hull, brown rice and bran than those harvested from unstressed counterparts, with an increase of 0.1% to 7.8% for hull, 3.4% to 11.9% for brown rice, and 0.3% to 11.2% for bran. While brown rice was increased, milled rice was reduced in submerged 10 genotypes by 0.3% to 15.1%, indicating that increased brown rice was due to more bran present in the rough rice of stressed genotypes. Submergence stress resulted in more broken grains for eight genotypes, and less head rice for five genotypes. Chalky grains was significantly increased by submergence stress, the magnitude varies with genotype, ranging from 0.1%-7.6%. Submergence stress reduced amylose content by 0.1% to 7.0% depending on genotype. Gelatinization temperature as determined by alkali spreading was also reduced in eight, but increased in the other four submerged genotypes. Submergence stress increased crude protein in all genotypes, ranging from 0.5% to 2.5%. With submergence stress significantly affecting grain quality traits, palay samples from both stressed and favorable environment should be considered when doing evaluation and selection of breeding lines for submergence-prone ecosystem.