4.3 Physical mechanisms of grain yield penalty caused by WL4
We found that the greatest reductions in grain yield occurred when waterlogging treatment was applied close to heading, even though the duration of waterlogging was very short (WL4; Fig. 2). This finding is in line with previous results (de San Celedonio et al., 2014; Setter & Waters, 2003). For WL4, lower grain yield was attributed lower grain weight and to a lesser extent, lower kernels per spike. In this treatment, waterlogging caused premature leaf senescence in waterlogging sensitive genotypes. It has been reported that reduced leaf greenness coincides with lower stomal conductance (Araki, Hamada, Hossain, & Takahashi, 2012), photosynthetic rate (Hossain et al., 2011) and water-soluble carbohydrates (Araki et al., 2012). Assimilate from photosynthesis and remobilization of culm residual water-soluble carbohydrates reserves are important for grain filling in crops (Kamran et al., 2020; Schnyder, 1993). Therefore, reduced carbon assimilation rates and lower remobilization of culm reserves in waterlogged plants may have resulted in lower grain growth rate during the grain-filling period of WL4.