Evaluation of morpho-physiological and yield-associated traits of rice (Oryza sativa L.) landraces combined with marker-assisted selection under high temperature stress and elevated atmospheric CO2 levels

Rice (Oryza sativa L.) has a tremendous domestication history and is presently used as a major cereal all over the world. In Asia, India is considered as one of the centers of origin of indica rice and has several native landraces, especially in North-Eastern India (NEI), which have the potential to cope with the negative impact of present-day climate change. The current investigation aimed to evaluate the NEI rice landraces potential under high temperatures and elevated CO2 levels in comparison with a check variety for phenological, morphological, physiological and yield-associated parameters and molecularly validated with marker-assisted genotyping. The initial experiment was carried out with 75 rice landraces to evaluate their high heat tolerance ability. Seven better-performing landraces along with the check variety (N22) were further evaluated for aforesaid traits across two years (2019 and 2020) under control (or T1) and two stress treatments - (i) mild stress or T2 [CO2 550 ppm + 4{degrees} C more than ambient temperature] and (ii) severe stress or T3 [CO2 750 ppm + 6{degrees} C more than ambient temperature] using bioreactors. In the molecular analysis, the eight selected genotypes were evaluated through 25 Start Codon Targeted (SCoT) markers. The results revealed that the mild stress (T2) had a positive impact on various morpho-physiological parameters like plant height, number of leaves, leaf area and yield parameters like spikelets panicle-1 (S/P), thousand-grain weight (TGW) and grain yield (GY). This effect could be attributed to the genotypes ability to maintain a higher photosynthetic rate and possess better tolerance ability to moderately high temperatures. However, under high-temperature conditions in T3, all genotypes exhibited a significant decrease in the studied parameters including GY. It was found that pollen traits were significantly and positively correlated to spikelet fertility% at maturity, which was further significantly associated with GY under applied stress conditions. The physiological traits including shoot biomass were evident to have a significant positive effect on yield-associated parameters like S/P, harvest index (HI), TGW and GY. Overall, two landraces Kohima special and Lisem were found to be better responsive compared to other landraces as well as the check variety N22 under stress conditions. SCoT genotyping amplified a total of 77 alleles out of which 55 were polymorphic with the PIC value ranging from 0.22 to 0.67. The investigation suggests the presence of genetic variation among the tested rice lines and further supports evidence of the closely relatedness of Kohima special and Lisem. These two are two better-performing rice landraces from North-East India based on their improving morpho-physiological parameters and yield attributes in mild and severe high temperature and elevated CO2 stress environments. The shortlisted two rice landraces can be used as valuable pre-breeding materials for future rice breeding programs to improve the stress tolerance properties, particularly to high temperatures and elevated CO2 levels under ongoing changing climatic scenarios.