Genotypes with enhanced expressions of acquired tolerance mechanisms showed improved growth under stress

Cultivation of rice under aerobic systems saves considerable irrigation water but the plants experience atmospheric (high VPD) and soil moisture stress between irrigations. Cultivars with enhanced expression of acquired cellular level tolerance mechanisms adapt well to this ecosystem. In this study genetic variability in acquired tolerance was studied in rice cultivars under different stress conditions. Amongst the six cultivars, KMP-153 and AC39020 showed significantly higher tolerance to PEG, NaCl stress and higher seedling vigour under accelerated ageing conditions. These genotypes maintained higher cell viability as measured by TTC reduction assay compared to the susceptible genotypes BPT5204 and Telahamsa. Similarly, the pot grown 30-day old plants were exposed to a gravimetry based gradual dry down protocol by maintaining soil moisture status similar to all the genotypes during the stress development and subsequently when the plants were maintained at desired soil moisture status, 60, 40% FC. Under similar moisture stress conditions expression of ROS scavenging enzymes SOD and APX, and dehydrin proteins LEA 14 and chaperons BiP-1 was significantly high in these tolerant lines. These resistant cultivars maintained higher photosynthetic rate and accumulated less MDA and also showed sustained growth under stress. The rice genotypes KMP-153 and KMP-175 which showed higher growth under PEG, NaCl stress and under AA also showed higher biomass and photosynthetic rates under drought conditions. These results reveal that by imposing stress similar to all genotypes and exposing to the induction stress or by gradual stress imposition prior to severe stress intrinsic variability in acquired tolerance mechanisms across the genotypes can be assessed. Genotypes with enhanced expression of acquired tolerance mechanisms showed higher tolerance to stress both at seedling stage and in pot grown plants.