The relationship between ash content and carbon isotope discrimination (Δ) was studied in durum wheat (Triticum durum Desf.) grown in a Mediterranean region (Northwest Syria) under three different water regimes (hereafter referred to as environments). In two of these environments, 144 genotypes were cultivated under rain-fed conditions. In the third environment, 125 genotypes were cultivated under irrigation. Ash content was measured in the flag leaf about 3 weeks after anthesis, whereas Δ was analysed in mature kernels. Total transpiration of the photosynthetic tissues of the culm contributing, from heading to maturity, to the filling of kernels was also estimated. Leaf ash content, expressed either on dry matter or leaf area basis or as total ash per blade, correlated positively (p< 0.001) with Δ in the three environments. However, this relationship was not the result of a positive correlation across genotypes between Δ and tissue water content. Moreover, only a small part of the variation in Δ across genotypes was explained by concomitant changes in ash content. When all genotypes across the three environments were plotted, Δ and ash content followed a non-linear relationship (r2 = 74), with Δ tending to a plateau as the ash content increased. However, for the set of genotypes and environments combined, total ash content per leaf blade was positively and linearly related (r2 = 0.76) with the accumulated culm transpiration. The non-linear nature of the relationship between ash content and Δ is sustained by the fact that culm transpiration also showed a non-linear relationship with kernel Δ. Therefore, differences in leaf ash content between environments, and to a lesser extent between genotypes, seem to be brought about by variations in accumulated transpiration during grain formation. and J. L. Araus ... [et al.].
Heat stress has become more common in recent years, limiting wheat production in Huang-Huai-Hai plain in China. To identify the effect of long-term heat stress on wheat production, two heat-resistant (JM44, JM23) and two heat-sensitive (XM26, GC8901) wheat varieties were sown in heat tents and normal conditions, and heat stress (9 to 12℃ higher than control) was imposed for seven days at post-anthesis. All varieties under heat stress exhibited early senescence and reduced grain-filling rate, while the grain-filling period of heat-tolerant varieties was longer than that of the heat-sensitive. Furthermore, long-term heat stress significantly reduced kernel mass, grain number, harvest index, chlorophyll content, maximum quantum yield of PSⅡ photochemistry, effective quantum yield of PSⅡ photochemistry, photosynthetic rate, and transpiration efficiency. In addition, the distribution of dry matter to vegetative organs, catalase activity, and malondialdehyde content increased. These results indicated that the lesser yield reduction of heat-resistant varieties (11-26%) than that of heat-sensitive (16-37%) is due to relatively higher antioxidative and photosynthetic performance and higher assimilation in the grain from vegetative organs.