Waterlogging at jointing and/or after anthesis in wheat induces early leaf senescence and impairs grain filling

Waterlogging may be involved in the grain-filling disorder known as 'abnormal early ripening' (AER) in wheat (Triticum aestivum) in western Japan. This study carried out over two consecutive cropping seasons (2009/10 and 2010/11), examines whether or not wheat plants exposed to waterlogging at jointing exhibit early leaf senescence during grain filling. The effects of a single waterlogging at jointing (WLjoint) or after anthesis (WLanthe), and of a double waterlogging at the same two stages (WW) were compared in three Japanese wheat cultivars. Waterlogging for 21 days was imposed in all cases except for after anthesis in 2010/11 when the treatment was for only 11 days. In both cropping seasons, grain yield in the WLjoint plants was 10-15% lower than that in the well-drained plants. The lower yields were due to smaller grain weights, rather than to decreases in spike number or grain number per spike. The WLanthe treatment also reduced yield by 15%, although the duration of stress in the WLanthe plots was 10 days shorter than in the WLjoint, plots. This indicates that the WLanthe treatment had a more negative impact on yield. Plants in the WW plots exhibited reductions in grain yield of from 22 to 35% depending on the cultivar. The smaller grain weights of waterlogged plants was a result of both a 1-5 days shorter grain-filling period and also lower grain growth rates in the later stages of filling. Plants in the WLjoint and WW plots did not show reductions in leaf greenness, stomatal conductance or leaf water content during or after waterlogging at jointing. However, the plants in the WLjoint and WW plots,and also in the WLanthe plots, suffered reductions in these parameters about 14 days after anthesis. At the same time, the plants in the WW plots showed the most marked leaf senescence and the lowest leaf water contents (0.39 g g(-1) in the WW plots vs 0.85 g g(-1) in the well-drained plots). At maturity, concentrations of water-soluble carbohydrates (WSCs) in culms were highest in the WW plots, probably indicating that remobilization of the WSCs from the culms to the grains was reduced. These results indicate that root injury by waterlogging at jointing induces rapid leaf senescence in the grain filling period. Comparisons among the WLjoint, WLanthe and WW plots indicate that in wheat, root sensitivity to waterlogging rises markedly during the post-anthesis period. (c) 2012 Elsevier B.V. All rights reserved.