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.     

Identification and phenotypic characterization of γδ T cells in rat lymph

γδ T cells represent an unconventional subset of T lymphocytes that are abundant in epithelial tissues and serve as an early immune defense against microbes. We have, for the first time, identified γδ T cells in steady-state thoracic duct lymph (TDL) from rats. The lymph contains γδ T cells expressing CD8 but not CD4, CD25, MHC-II or CD103. The percentage of TDL γδ T cells in rats does not change when the mesenteric lymph nodes (MLN) are surgically removed. Our data suggest that a proportion of γδ T cells migrate from the intestine into rat TDL, under steady-state conditions.     

Tolerance of longer-term partial stagnant flooding is independent of the SUB1 locus in rice

Longer-term partial stagnant flooding, particularly when it occurs following transient complete submergence causes severe damage to modern rice varieties. Progress was made in developing varieties tolerant of complete submergence through transfer of the Submergence-1 (SUB1) gene into popular varieties. However, SUB1 may not be effective under partial stagnant flooding (SF), as the new varieties may not elongate and continue growth when fully or partially submerged because of the SUB1-mediated suppression of elongation. We tested a set of rice genotypes, including a pair of near-isogenic lines (NILs), Swarna and Swarna-Sub1, under either SF or SF following complete submergence of 12 d. Swarna-Sub1 had higher survival and yield than Swarna following 12 d of submergence, but survival and grain yield of all lines decreased substantially when SF of 15-30 cm followed complete submergence, with the sensitive lines experiencing greater reductions in growth and yield. This suggests the importance of combining SUB1 with tolerance of SF in areas where both stresses are expected during the season. Swarna and Swarna-Sub1 are more sensitive to long-term partial SF than IR49830 and IR42 because of their short stature, and Swarna-Sub1 showed slightly higher reduction in tillering than did Swarna when subjected to deeper SF alone, possibly because of further inhibition of elongation by SUB1 if induced in submerged tissue. The results suggest that tolerance of these genotypes to SF depends less on SUB1 introgression and more so on the genetic background of the recipient genotype, with better performance of the genotypes that are inherently taller, such as IR42 and IR49830. The SUB1 donor landrace FR13A and its derivative breeding line IR49830 had better survival and relatively less reduction in grain yield under SF following complete submergence and under longer-term partial SF, indicating that these genotypes may have genes other than SUB1 for submergence and SF tolerance. For better adaptation to prolonged SF, SUB1 should be introgressed into genotypes that tolerate partial SF through better tillering ability and taller shoots, because SUB1 may not be effective in shorter genotypes, as it promotes survival of submerged plants by hindering shoot elongation to conserve energy reserves. Varieties combining tolerance of prolonged SF with SUB1 will have broader adaptation in flood-prone areas and greater impacts on yield stability.     

Physiological Mechanism and Nutrient Management Strategies for Flood Tolerance in Rice Grown in Lowland Flood Prone Ecosystem

Journal of Crop Science and Biotechnology - In flood-prone areas, rice must have flood tolerance characteristics either through genotypic selections or by nutrient application management...