Growth, productivity and grain quality of AG1 and AG2 QTLs introgression lines under flooding in direct-seeded rice system

Early flooding after direct seeding induces anaerobic condition during germination or anaerobic germination (AG), which severely reduces crop establishment in both rainfed and irrigated areas. Seeds germinating in flooded soils could encounter hypoxia or even anoxia in severe cases, and this hinders germination and seedling growth. The study evaluated the effects of incorporating two major QTLs, AG1 and AG2, associated with tolerance of flooding during germination into the background of two popular rice varieties and assessed their interactive effects on enhancing crop establishment, and subsequent growth, grain yield and quality under direct seeded rice (DSR) system. Elite near-isogenic lines incorporating QTLs of major effects on AG tolerance (AG1, AG2 and AG1 + AG2) in the backgrounds of the popular varieties PSBRc82 (PSBRc82-AG1, PSBRc82-AG2, PSBRc82-AG1-AG2) and Ciherang-Subl (Ciherang-Subi-AG1, Ciherang-Subl-AG2, Ciherang-Subl-AG1-AG2), along with the donors Kho Hlan On (KHN for AG1) and Ma-Zhan Red (MZR, AG2) and the recipients PSBRc82 and Ciherang-Subi were grown either under saturated soils or flooded with 3 - 5 cm water depth immediately after dry seeding. Flooding substantially reduced seedling emergence, survival, plant biomass, grain yield and yield components across genotypes. The reduction in yield was more drastic in the sensitive genotypes. The significant decline in grain yield was mainly attributed to reductions in number of panicle per unit area. The AG1, AG2 QTLs are effective in conferring tolerance of early flooding during germination. AG1 and AG2 introgression lines showed a yield advantage of up to 2.8 t ha(-1), under early flooding compared with their recurrent parents. Apparently, introgression of AG1 and AG2 QTLs did not have any negative impact on performance under saturated (control) and flooded conditions with respect to seedling emergence, growth, and yield, though with effect on chalkiness in some backgrounds, which warrant further studies.