Agricultural Horizons: Research, Technology and Sustainable Development Vol. 1

Rice (Oryza sativa L.) is a primary food source for people in Asia. However, rice varieties developed for desirable agronomic traits are susceptible to both biotic and abiotic stresses. Under stress conditions, the growth of rice plants is weakened, and grain yield subsequently declines to an unacceptable level. In rain-fed rice-growing areas, submergence is an economically important form of water stress. Under rapidly changing climatic conditions associated with continuous warming of the earth’s surface, flooding is becoming an unavoidable constraint to rice cultivation. Therefore, rice breeders have sought to improve popular developed rice varieties for submergence tolerance worldwide by using available, highly efficient stress-tolerance QTLs through conventional methods to manage the negative impact of climate change on rice crops. In the present study, two developed short-duration rice varieties, ADT36 and ADT37, were improved for submergence tolerance at the seedling stage through introgression of the Sub1 locus via conventional methods. These varieties are highly popular in the Cauvery delta region of Tamil Nadu, India. This study was carried out in the net house of Kandaswami Kandar’s College, Tamil Nadu (11.1202ºN, 78.0031°E). In the parental polymorphism study, variation between recipient and donor parents was confirmed at the phenotypic and genotypic levels. In phenotypic selection, the parental lines were differentiated as tolerant or susceptible based on the rate of shoot elongation under submergence conditions. In genotypic selection, an InDel marker located within the Sub1 locus was used to differentiate the parental lines. After hybridisation, submergence-tolerant rice progenies were selected by comparing rice lines with the Sub1 locus in the F₁, BC₁, BC₂ and BC₃ generations under submergence-stress conditions. Tolerant rice progenies were selected solely on the basis of their performance under stress conditions. Finally, the presence of the Sub1 locus in the BC₃F₁ generation was confirmed by PCR amplification using a foreground marker in 7 and 6 rice progenies of ADT36 and ADT37, respectively. These positive progenies were allowed to self-pollinate to produce BC₃F₂ seeds. During the evaluation of near-isogenic lines (NILs), some NILs of both varieties showed stability of the Sub1 locus under stress conditions. Therefore, improved NILs of ADT36 and ADT37 can be used in the Cauvery delta region to enhance rice production under submergence-stress conditions.