ROOT AND SHOOT GROWTH, WATER-USE AND WATER-USE EFFICIENCY OF SPRING DURUM-WHEAT UNDER EARLY-SEASON DROUGHT

One of the common features of the Mediterranean climate of North Afric a is the uncertainty of rainfall immediately after durum wheat (Tritic um durum Desf.) emergence, leading to early-season drought. Impacts of drought during wheat reproductive development have been thoroughly in vestigated, while studies of early-season drought are lacking. The obj ectives of the research reported here were to examine genotypic differ ences for some morphological traits in response to early-season drough t, and to determine the association of these traits with water use, wa ter use efficiency in producing grain (WUEg) and dry matter (WUEdm). E xperiments were conducted under field conditions on a Vertic Calicixer ol. Four cultivars and two advanced lines of spring durum wheat were s ubjected to four water regimes, including a well-irrigated control and three water stress treatments. The three water stress treatments were imposed by withholding water during the period from emergence to eith er the onset, middle or the end of tillering. Subsequently, irrigation was used to provide adequate soil moisture for the remainder of the g rowing season. Total water use, WUEg, and WUEdm were weakly associated with root length density. Under drought stress conditions WUEg and WU Edm were positively associated with relative growth rate under stress, relative growth rate upon recovery and shoot dry matter yields early in the season. To develop new cultivars with improved early vigor, veg etative biomass and WUEg, as proved in this study, wheat breeders need to utilize parent materials with considerable improvements in these c haracteristics. ((C) Inra/Elsevier, Paris.).