Morphology and Dry Matter Accumulation in Rice (Oryza sativa L.) Seedlings Under Drought Conditions

Drought is one of the main limitations of rice (Oryza sativa L.) productivity and is a severe problem in many regions in the world. In Vietnam, drought affects approximately 22% of the area under rice cultivation and usually occurs during the vegetative stage. One of the difficulties in breeding rice for drought tolerance is the lack of genotypic variation among rice populations. In this study, seedlings of 172 rice varieties from different regions around the world were screened under drought and non-drought conditions in order to explore response to drought stress among different rice genotypes. Considerable variation in the leaf rolling index (LRI), shoot dry weight, root dry weight (RDW), shoot length (SL), root length (RL), and drought resistance index (DRI) was found between rice varieties over two screening periods. There were positive correlations between DRI and drought to control ratios in RDW, SL, and RL. A negative correlation between DRI and LRI among varieties suggested that LRI might be useful a drought tolerance indicator in rice seedlings. These negative correlations were greater in early afternoon observations than in morning observations. Correlations were also greater in the early stages of drought stress than under severe drought. These results indicate that leaf rolling should be observed in the early afternoon (when drought stress is at its daily maximum) and in the early stages of drought development, before stress becomes severe.