부산대학교 도서관

Rice is one of the most important global staple foods. Due to freshwater scarcity and rapid increase in food demand in the world, it will be necessary to produce more food using less water. Alternate wetting and drying (AWD) irrigation is a promising technology for rice agriculture which potentially increases plant water use efficiency (WUE) whilst maintaining yield. A reproducible AWD system was designed in an environment-controlled growth room to facilitate the study of water use, physiological traits, ionome profile in soil and rice, and gene expression in rice in response to AWD compared to a conventional continuous flooded (CF) system. After successfully standardizing the experimental design, an AWD experiment was conducted using six genotypes (BRRI Dhan 28, ARC 5977, BJ 1, TEPA BORO 508, AUS 105 and Pachodi 427) with four replications. The main aim of the study was to understand the factors that might regulate growth and yield under AWD, along with the study of ionomics and transcriptomics to get an insight into how AWD affects shoot growth and yield. The AWD treatment reduced water use by 30-45% compared to CF. An overall increase in grain yield of 15% under AWD was achieved, along with significant increases in panicle weight and harvest index under AWD compared to CF. The plants grown under AWD had altered element concentration in grains, with a decrease in grain cadmium, manganese, cobalt, nickel and copper, but an increase in grain iron under AWD compared to CF. To identify the genes differentially expressed between genotypes and treatment, shoot transcriptome analyses of BRRI Dhan 28, BJ 1, TEPA BORO 508 and Pachodi 427 were performed, during 5th AWD cycle at 3rd time point (when water level was 9 cm below the soil surface). The analysis revealed 696 DEGs, with the evidence of genotype by treatment interaction. A large variation in number of DEGs between the genotypes was observed, demonstrating a large impact of AWD on BRRI Dhan 28 and a small effect on BJ 1, TEPA BORO 508 and Pachodi 427. The DEGs are involved in processes such as photosynthesis, chlorophyll biosynthesis, stomatal complex morphogenesis, oxidation-reduction process and carbohydrate metabolic process. In conclusion, an AWD system was successfully designed that could be replicated in a controlled environment. AWD increased yield, WUE and modified soil nutrient availability mostly changing with redox corresponding to the altered wet and dry cycles. Relatively small differences in grain nutrient composition were observed, some of them contradictory in direction to other studies. Differential gene expression analysis demonstrated a subtle impact of AWD on gene expression in the shoot, and that is, at large if not all, photosynthesis related genes. Overall, the study suggests that AWD is a mild environmental treatment for which major breeding effort for adaptation is not likely to be needed.