Rice (Oryza sativa L.) is an important food crop in the Asian countries, but it is severely affected by submergence stress from seed germination to reproductive stage during heavy monsoon period every year in some parts of the world. This situation has created to improve highly preferable rice varieties for submergence stress tolerance. In the present study, two short duration rice varieties, ADT36 and ADT37 were improved for submergence tolerance at seedling stage using CR Dhan 801 with Submergence 1 (Sub1) locus as donor up to BC3F2 generation through marker assisted backcross method. In Tamil Nadu state, these two rice varieties are adapted in the Cauvery delta region wherever submergence and drought stress is erratic. Seeds from this generation were evaluated for submergence tolerance at seed germination stage. At parental level, we noted less and more elongation in the coleoptile growth of donor and both recipient parents under anaerobic condition, respectively when compare to aerobic condition. In the evaluation of BC3F2 population, we found a range in the elongation of coleoptile and root length under anaerobic condition. From these, a number of seven rice lines (ADT36- F12-5-19.6; ADT36- F12-13-7.11,13,14, ADT36- F14-5-3.4, ADT36- F14-16-2.6, ADT36- F15-2-5.1) for ADT36 and four rice lines (ADT37- F113-27-5.2, ADT37- F115-2-1.1, ADT37- F115-2-2.5, ADT37- F115-2-2.7) for ADT37 rice variety were found to be superior in coleoptile elongation compared to donor line. These rice lines at seed germination stage followed quiescence strategy like donor parent having Sub1 associated with seedling stage tolerance and they possessed decreased growth under submergence condition. Further, other lines exhibited escaping mechanism under flooding with higher rate of CL and RL. Thus, selected rice lines harboring Sub1 locus linked with submergence tolerance at seedling stage will support for flood tolerance at seed germination stage also in the genetic background of ADT36 and ADT37. Therefore, in future, these lines can be used in both methods of direct seed sowing and transplanting in upland and lowland rice cultivating areas and as a genetic source in the rice breeding program.

Submergence tolerance, anaerobic seed germination, Cauvery delta areas, ADT36, ADT37, CR Dhan 801. Coleoptile and Leaf elongation

In the present study, we found the difference between the donor and recipient parent based on low and high rate of coleoptile elongation under flooding, respectively. Shoot elongation under flooding which results in consumption of stored starch content very fast and it leads to plant death or lodging following the de-submergence. According to the previous studies, Sub1 locus is linked with only submergence tolerance at seedling stage and it controls the degradation of starch due to shoot elongation but not at seed germination. Elongation of coleoptile in ADT36 and ADT37 rice variety during seed germination associates with SNORKEL 1 and SNORKEL 2 (SK1/2)-dependent escape strategy and CR Dhan 801 with SUBMERGENCE 1A (SUB1A)-dependent quiescence strategy. However, we found both strategies in BC3F2 population. Supportively, in a very recent study, rice line pyramided with AG and SUB1 gene has showed negative impact on shoot elongation. Here also, we found difference in flood tolerance between ADT36 and ADT37 i.e. when compare to ADT36, elongation of coleoptile is found to be decreased and increased under flooding and non-flooding condition, respectively. Thus, this study reveals that expression of gene/QTL depends on the genetic background of a rice variety. Further, the screening process of existing genetic source may lead to a way to some other stress tolerance also.

Salomi R., Vignesh P. and Bharathkumar S. (2023). Screening of BC3F2 Rice population for Submergence Tolerance During Seed Germination. Biological Forum – An International Journal, 15(11): 243-248.