Physiological attributes associated with early-season drought resistance in spring durum wheat cultivars

One of the common features of the Mediterranean climate in North Africa is the uncertainty of rainfall immediately after wheat (Triticum durum Desf) emerges. Relatively little work has been done to compare the drought resistance of spring durum wheat cultivars under early-season drought stress. There is a limited insight into the physiological basis of spring durum wheat drought resistance in rainfed Mediterranean regions. Field experiments were conducted in 1995 and 1996 growing seasons, and a greenhouse experiment was conducted in 1996 to examine differences in some physiological characters among six spring durum wheat cultivars in response to different durations of early-season drought, and rewatering; and to determine the relationships of these characters to drought resistance. Six spring durum wheat cultivars were evaluated under four water regimes. Water regime treatments were: a well-irrigated treatment; and three water deficit treatments imposed during the period from emergence through either the onset of tillering, mid-tillering or the end of tillering. Cultivars differed widely in their response to early season water stress. Under drought stress conditions, grain yield, aboveground dry matter yield, water use efficiency for the grain (WUEg) and for the total dry matter (WUEdm) were strongly positively associated with net CO2 uptake:transpiration ratio (A/E), and osmoregulation capacity. It is concluded that drought-induced changes in A, A/E, stomatal resistance, and osmotic adjustment are possible key control points in determining the drought-resistance of a cultivar. Furthermore, there is a substantial degree of intraspecific variation for the above mentioned physiological attributes to explore as a selection tool. Selection for high osmoregulation capacity and high A/E ratio would seem to be a justifiable means of improving total dry matter and grain yield under conditions of early-season water stress.