Agronomic manipulations can enhance the productivity of anaerobic tolerant rice sown in flooded soils in rainfed areas

Poor seedling emergence and establishment are a major restraint for adopting direct seeding in rice. This is especially critical in rainfed lowlands where floods can occur immediately after sowing, creating anaerobic conditions during germination and early seedling growth. Developing rice cultivars that can germinate in flooded soils will ensure good crop establishment. Several major quantitative trait loci (QTLs) for tolerance of anaerobic conditions during germination (anaerobic germination; AG) were identified from different landraces; and near isogenic lines (NILs) containing one of these QTLs (qAG-9-2, AG1) in the background of IR64 were developed. This study is an attempt to determine the effectiveness of AG1 QTL in improving germination of two IR64-AG NILs; IR 93312-30-101-20-3-66-6 (IR64-AG131) and IR93312-30-101-20-13-64-21 (IR64-AG132) sown under flooded conditions. The study also evaluated selected agronomic practices anticipated to further enhance crop establishment in flooded soils. IR64-AG NILs showed 81% and 217% higher plant populations over IR64-Sub1 and IR64, respectively, and this was also reflected as significantly higher grain yields. IR64-AG NILs mobilized relatively more starch into soluble sugars while submerged and maintained higher soluble sugar supply to the developing embryo resulting in faster and higher germination rates than the non-AG genotypes. Agronomic manipulations like higher seed rate (60 kg ha−1), better seeding methods and nutrient application improved seedling growth after germination and emergence, increasing plant height, leaf area, number of tillers and biomass accumulation. These improvements were reflected as higher grain yield even in the intolerant cultivar IR64. Application of 20% more phosphorus with the recommended N-P-K resulted in 21%, 16% and 19% higher grain yield in IR64-AG, IR64-Sub1 and IR64, respectively, over the control. The results established that combining proper crop establishment practices with tolerant genotype could enhance crop establishment in flooded soils using direct seeding methods, with consequent reduction in production costs and water use and subsequent increase in farmers' income.