MORPHOLOGICAL ATTRIBUTES ASSOCIATED WITH EARLY-SEASON DROUGHT TOLERANCE IN SPRING DURUM-WHEAT IN A MEDITERRANEAN ENVIRONMENT

Impacts of drought during the reproductive development phase of wheat have been thoroughly investigated, while studies of the early-season d rought effects are lacking. Field experiments were conducted to study the effect of duration of drought stress during the period from emerge nce to the end of tillering on the growth and performance of different wheat cultivars, and to identify traits that could be associated with the resistance to early season drought. Experiments were conducted on a Vertic Calcixerol soil in the semiarid cereal-growing region of Mor occo in 1995 and 1996. Six spring durum wheat (Triticum durum Desf.) c ultivars selected on the basis of variation in morphology, phenology, and zone of adaptation were subjected to four water regimes, including a well-irrigated control. The three water stress treatments were impo sed by withholding water during the period from emergence to either th e onset, middle, or the end of tillering. Subsequent irrigations provi ded adequate soil moisture for the remainder of the growing season. Re sults from both years were generally consistent. The differential resp onses of the six cultivars was mainly due to differences in numbers of kernels produced. High yields under early-season drought were attribu ted to high leaf area index under stress and, upon recovery, and to hi gh tiller survival rate. The consistency observed over years in the re lationships between grain yield and those traits that proved to be mos t associated with the resistance to early-season drought, would sugges t the usefulness of these traits as selection criteria for breeding fo r improved drought resistance in a Mediterranean climate type of North Africa.