Responses of SUB1 rice introgression lines to submergence in the field: Yield and grain quality

Prolonged submergence is a major constraint to rice production, affecting over 15 million ha in South and Southeast Asia and causing an annual yield loss of over US$ 600 million. This is because all the modern high-yielding rice varieties are sensitive to complete submergence. A major quantitative trait locus (QTL), SUB1, associated with submergence tolerance, was mapped on chromosome 9 and recently bred into popular rainfed lowland rice varieties sensitive of complete submergence, using marker-assisted backcrossing (MABC). Here, we assessed the impact of introgressing SUB1 into three rice varieties popular in farmers’ fields of South and Southeast Asia, Swarna, Sambha Mahsuri, and IR64, under control conditions as well as following submergence in the field. Under control conditions, no differences were observed between Sub1 introgression lines and their recurrent parents in grain yield or quality aspects. Submergence substantially delayed flowering and maturity, and reduced grain yield, shoot biomass, harvest index, and yield components across cultivars. The reduction in yield was more drastic in the sensitive varieties, particularly when submerged for longer duration (17 d). The significant decline in grain yield was mainly attributed to reductions in grain filling, number of grains per panicle, and grain weight. The SUB1 QTL is effective in conferring tolerance of submergence for about 12–17 d, depending on floodwater conditions. Sub1 introgression lines showed a yield advantage of up to 3.8 t ha⁻¹ and slightly better grain quality after submergence compared with their parents. Apparently, the introgression of SUB1 into popular varieties did not have any negative impact on their performance under control conditions but considerably enhanced their yield and grain quality following short-term submergence.