Responses of rainfed lowland rice genotypes to terminal drought in Northeast Thailand

บทคัดย่อ

In Northeast Thailand, rainfed lowland rice often experiences terminal drought that develops around flowering and become severe during the flowering-grain filling stage. Two drought (drought trial 1 and 2) and well irrigated control trials were conducted with 35 genotypes of rainfed lowland rice to determine the traits that contribute to high yield under water - limitinged conditions, particularly the importance of roots system development under terminal drought conditions. In drought trial 2 a gravel layer was added at 10-20cm below the soil surface to discriminategenotypes for deep rooting, while in drought trial 1 there was no gravel layer.Genotypic consistency in root mass and number between the two trials was examined and implication of well-developed root system on growth determined. Because of the long duration of the terminal drought grain yield was more severely affected in later flowering genotypes particularly in drought trial 1. On the other hand, in drought trial 2 with the gravel layer, some late flowering genotypes which had more extensive root systems, i.e. larger root mass and root number were able to produce higher yield than others and they generally had shorter delay in flowering. Correlation analysis suggested that genotypes with more extensive root system were able to maintain higher leaf water potential which resulted in maintaining larger panicle density. In drought trial 2, genotypes that maintained higher leaf water potential produced higher grain yield. It is thus suggested that adaptation of rainfed lowland rice to terminal drought conditions can provide drought escape in general, but also more specifically, certain types of rainfed lowland and certain methods of cultivation (such as adding a gravel layer) can provide an avoidance mechanism through extensive root system development to maintain better plant water status, and therefore survive terminal drought. Under the drought trial 2 where grain yield level was higher than trial 1, delay in flowering is shown to be a trait that could be used as a selection criterion.