Effects of water stress on dry matter accumulation and translocation in winter wheat cultivars planted at different ages

Water shortage seriously threatens sustainable agriculture development across the globe. Winter wheat (Triticum aestivum L.) is the largest water user and wheat production is often limited by water scarcity and uneven distribution of precipitation in Henan Province. Winter wheat grain yield is mainly formed by dry matter accumulation and redistribution in vegetative organs during pre- and post-anthesis. Water conditions have significant effects on dry matter accumulation, distribution ratios of dry matter among various organs and hence grain yield. Therefore knowledge of the changes in dry mater associated with genetic gains is required for understanding yield-limiting factors and determining future breeding strategies. However, few available data exist on the mechanisms of effects of different water regimes on dry mater accumulation and translocation in wheat. The objective of this study was to determine the effects of water conditions on the characteristics of dry matter accumulation and translocation in winter wheat cultivars planted at different ages. The results provided the needed valuable information for further improvements in grain yield and determination of future breeding strategies of wheat in China. Six representative winter wheat cultivars (planted in the 1950s, the 1960s, 1970s, 1980s, 1990s and 2002-2003) were used under similar conditions in the 2011-2012 growing season. The three water regimes used were as follow: control (CK) at 75%~85% of field capacity, mild water deficit (MD) at 60%~70% of field capacity, and severe water deficit (SD) at 45%~55% of field capacity. Results showed that genetic improvement optimized dry matter distribution at different growth stages in winter wheat and well balanced dry matter contribution to grain during pre-anthesis and post-anthesis. Dry matter accumulation and translocation in winter wheat before and after anthesis increased in modern cultivars. Furthermore, reduced dry matter assimilation in modern cultivars increased grain production after anthesis. Modern cultivars were shorter in height and peduncle than old cultivars. Modern cultivars improved the 1000-grain weight, harvest index and grain yield. Increase in winter wheat grain yield was mainly related to increase in the 1000-grain weight, which further led to a significant increase in harvest index under constant total biomass accumulation in the year. The 1000-grain weight and harvest index were positively related with yield improvement. Compared with wheat cultivars planted in the 1950s, average height of winter wheat planted in the 1990s and 2002 under CK, MD and SD decreased by 35.2%, 36.2% and 38.2%, respectively. However, average 1000-grain weight increased by 31.7%, 17.4% and 56.3%, respectively. Also average grain yield increased by 40.4%, 43.0% and 52.4%, respectively. Harvest indexes of winter wheat cultivars planted in the 1990s and 2002 under CK, MD and SD were respectively 31.4%, 22.3% and 24.6% higher than those of wheat cultivars planted before the 1980s. Dry matter accumulation in early cultivars was higher than that in modern cultivars from heading to anthesis under CK. Under MD and SD treatments, dry matter transfer at pre-anthesis in winter wheat cultivars planted in the 1990s and after was improved. Dry matter output to grain from stem increased in modern cultivars. Reduction in dry matter after anthesis was small and dry matter proportion was suitable in modern cultivars. This laid the basis for future increases in grain yield under water stress conditions.