Physiological and antioxidant responses associated with Sub1 gene introgressed rice (Oryza sativa L.) lines under complete submergence.

Rice is the only crop which is well adapted to aquatic environment but, it is unable to survive if completely submerged for several weeks. Breeding rice varieties with submergence tolerance is one of the best approaches to alleviate the adverse effect of submergence which requires the introgression of Sub1 gene into elite rice varieties. Hence, the study was undertaken to introgress submergence tolerant gene into the rice variety Jaya through Marker-Assisted Backcross Breeding. Also the physiological and biochemical responses like survival percentage, underwater shoot elongation, total carbohydrate content and superoxide dismutase activity were also studied in Sub1 introgressed lines. We could develop twenty Sub1 introgressed lines with Sub1 region of 3.1-5.1mb and with 80.0- 95.3% recurrent parent genome recovery. Sub1 introgressed Jaya lines and the tolerant checks FR13A and Swarna Sub1 had lower shoot elongation under water, higher superoxide dismutase activity (about 5 times) upto 4 h after de-submergence which resulted in higher survival percentage. The reduced shoot elongation of tolerant varieties reduced the utilization of stored carbohydrate. Through our research we introgressed Sub1 gene into rice variety Jaya through Marker-Assisted Backcross Breeding and could study the physiological responses under submergence by which we confirmed the presence of Sub1 gene in these lines. These lines could be field evaluated and could be released as a new variety thus helping the farmers of flood prone areas of Kerala.

Introgression of dual abiotic stress tolerance QTLs (Saltol QTL and Sub1 gene) into Rice (Oryza sativa L.) variety Aiswarya through marker assisted backcross breeding.

Salinity and submergence are two very prominent abiotic stress conditions affecting rice yield adversely in the coastal agro ecosystem. Marker Assisted Backcross Breeding (MABB) is an efficient and fast track molecular tool to incorporate a desired stress tolerant QTL/gene into an improved cultivar. The present study was carried out for the introgression of Saltol QTL responsible for salinity tolerance and Sub1 gene responsible for submergence tolerance into the high yielding rice variety Aiswarya independently through MABB. Final objective of the study is to develop dual stress tolerant (tolerance to salinity and submergence) Aiswarya rice variety by pyramiding the both target QTLs introgressed BC2F2 progenies having maximum background homozygosity. The donors of Saltol QTL and Sub1 gene used in the present study were FL478 and Swarna Sub1, respectively. Based on the background genome analysis of the introgressed plants, the plants with > 85-90% background similarity were selected for pyramiding of Saltol QTL and Sub1 gene into the elite background of rice variety Aiswarya. Those selected introgressed lines with Saltol QTL and Sub1 gene will be again crossed to pyramid both Saltol QTL and Sub1 gene into the rice variety Aiswarya. Such a mega rice variety pyramided with dual stress tolerant QTLs is the expected outcome of this study and can be recommended for cultivation in the flood prone saline coastal agroecosystem.