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Rice, often termed the golden cereal, sustains billions globally but faces submergence as a significant constraint in semi deep and deep-water ecosystems in India. The primary aim of this study was to evaluate the genetic potential of yield and yield-contributing traits in the cross ASD 16 x BIL of CO 51 Sub1 (12 x 9-7-6-12-3-45) across the F2 and F3 generations. The research revealed a wide range of variation for all traits in both generations. Specifically, positively skewed and platykurtic curves were observed for the number of productive tillers per plant and the number of chaffy grains per panicle, indicating the influence of a large number of genes with dominance-based gene interaction on these traits. The study also found highly significant correlation and regression coefficients for all recorded traits. Interestingly, while broad sense heritability showed high values for certain traits, narrow sense heritability percentages were only moderate for the same traits. Thus, focusing on selecting individuals based on narrow sense heritability would be more effective in improving those traits, as it targets the genetic variation that can be passed on to future generations. [ABSTRACT FROM AUTHOR]

Stagnant flooding (SF) is a serious threat for rice production in rainfed lowland areas of Southeast Asian countries. To overview the SF effect, photosynthetic performances and productivity were studied with three landraces (Ravana, Kamini, and Rashpanjor) and four high-yielding cultivars (Savitri, Savitri-Sub1, Gayatri, and Varshadhan) of rice under medium depth (40-50 cm) of water level. Stagnant flooding significantly increased the stem elongation and decreased yield and yield attributing parameters. The chlorophyll a fluorescence rises from O- to P-step with distinct J- and I-step were noticed in all the cultivars up to 75 d of SF. Prolonged flooding (> 2 months) perturbed both donor and acceptor side of PSII. Vitality indices (PIABS and PITOT) decreased greatly under prolonged SF. Analysis of O-J-I-P transients suggests that the information is useful for agricultural planning with the purpose to enhance rice yield under lowland medium depth SF. [ABSTRACT FROM AUTHOR]

Poor productivity of rice in rainfed lowlands is due to complete submergence as it is a major abiotic stress of these regions. For enhancing the rice productivity of these areas, better nutrient management options are required and results may even better when combined with stress tolerant cultivars, even when tested under natural conditions of farmers' field. For supporting the above statement, the effect of nitrogen and phosphorus in graded doses was evaluated for submergence tolerance in controlled conditions and the results obtained were tested and validated at farmers' field in Cuttack, Odisha, India. Shoot elongation, leaf senescence and lodging were lowest with the application of higher phosphorus (60 kg ha−1). Highest dose i.e. 100-60-40 NPK kg ha−1 resulted in higher plant survival of all the varieties by 90–170% over no nutrient application, it was also reflected in the higher growth after recovery, leaf greenness, leaf and stem growth, chlorophyll and carbohydrate concentrations and ultimately higher grain yield. At farmers' field, application of basal P, K and post-flood N management practice resulted in overall better performance of Swarna and Swarna-Sub1 showing higher yield attributes leading to 65.7 and 37.9% higher grain yield, over conventional practices followed by farmers. Apart from that results were more positive if post-flood nitrogen was applied as urea foliar spray might be due to quick absorption of N by plant leaves and also spraying helps in removing the silt of flood water sticking to the leaf surface and facilitated the plants to photosynthesize and survive after desubmergence. These cost-effective management options may enhance the productivity and profitability of rice in the flood-prone areas where farmers hesitate to apply nutrients. [ABSTRACT FROM AUTHOR]

The southern part of erstwhile Dhanushkodi township, Tamil Nadu, experienced subsidence and submergence during AD 1948-49. Shallow bathymetric and side-scan surveys together with sampling and underwater videography confirm the extent and quantum of subsidence. The studies reveal that a vertical tectonic movement (fault) parallel to the coastline with a displacement of ∼5 m led to the subsidence of the southern part of the township. This fault movement has occurred 57 years ago and hence could be the latest neo-tectonic movement ever recorded along the east coast of India. [ABSTRACT FROM AUTHOR]

A laboratory study at the Indian Agricultural Research Institute, New Delhi showed that DCD was an efficient nitrification inhibitor under field capacity moisture ( - 30 kPa) but not so under submerged soil conditions. Nitrification inhibition by DCD was 79.6% after 1 week of incubation and decreased to 59.3% after 3 weeks of incubation under field capacity moisture, while it was only 19.3% after 1 week of incubation and 10.6% and 18.4% after 2 and 3 weeks of incubation under submergence, respectively. DCD can play an important role in reducing N losses from agricultural fields. [ABSTRACT FROM AUTHOR]

We review a multidisciplinary approach to improve flooding tolerance in rice and, specifically, tolerance of complete submergence. Environmental characterizations in India and Thailand suggest that limited gas diffusion and, sometimes, low irradiance are the most important factors contributing to plant mortality. This supports the view that submergence tolerance of rice seedlings is related to maintenance of energy supply partly through fast rates of alcoholic fermentation which require high levels of carbohydrates. In germinating seeds, rates of coleoptile elongation during anoxia are highly correlated with rates of alcoholic fermentation and carbohydrate supply for energy production. In older seedlings, survival during submergence is highly correlated with carbohydrate supply.Optimization of growth vs. maintenance processes affects survival because elongation growth competes for energy and carbohydrate reserves essential for maintenance processes. This was demonstrated by experiments using: (a) cultivar comparisons, (b) growth regulators and (c) dwarf-mutants. Hence, submergence tolerance of 14-d-old rice seedlings can increase by up to 98% during 10 d submergence when elongation growth is reduced in these three ways. This is consistent with the observation that submergence tolerance and elongation ability rarely occur in the same genotype.Plant breeding has produced elite lines with up to four-fold greater yields and submergence tolerance equal to the world's most tolerant cultivars, but successful introduction of these elite lines in the field is elusive. Recent production of double haploid populations differing in submergence tolerance permitted testing of the physiological and genetic linkage of trails, or genes, with submergence tolerance. Genetics research with segregating populations of 15- to 50-d-old seedlings demonstrated (a) there is one dominant gene for submergence tolerance and (b) this gene is present in three out of four of the world's most tolerant rice cultivars. This suggests that a common factor related to tolerance of limited gas diffusion, (e.g. one of the enzymes of alcoholic fermentation) may be responsible for genotypic differences in submergence tolerance of rice. An alternative possibility is that a gene for a transcription factor is involved in the expression of a multiple gene cascade that confers submergence tolerance. [ABSTRACT FROM AUTHOR]