ONTOGENIC ANALYSIS OF YIELD COMPONENTS AND YIELD STABILITY OF DURUM-WHEAT IN WATER-LIMITED ENVIRONMENTS

One main reason for the slow improvement of durum wheat in water-limit ed environments is the lack of clear understanding of the interrelatio nships among yield components and their compensatory changes under low and erratic moisture availability. Five cultivars, varying in many ph ysiological attributes, were tested under different drought-stress con ditions in field and greenhouse experiments. The cause-effect relation ships of duration of vegetative period, duration of grain-filling peri od, number of spikes per m(2), kernels per spike, kernel weight and gr ain yield per m(2) were assessed. Furthermore, yield stability was eva luated. Yield reduction was largest under mid-season stress (58%), fol lowed by terminal stress (30%) and early stress (22%). Cultivar Po was very sensitive to terminal stress. Path-coefficient analysis revealed a complex pattern of relationships among the six variables. An increa se in vegetative period reduced the grain-filling period under all con ditions. It increased number of kernels per spike under non-stress con ditions. The direct effect of spikes per m(2) on grain yield was signi ficantly positive. However, more spikes per m(2) resulted in fewer ker nels per spike and a low kernel weight and, as a result, a negative re lationship with grain yield under early stress. Grain-filling period h ad a strong influence on grain yield via kernel weight. Kernels per sp ike had the largest direct effect on grain yield. However, it was nega tively correlated with kernel weight, especially under terminal stress . Grain yield heavily depended on kernels per spike under early stress and grain-filling period and kernels per spike under terminal stress. Variation in drought susceptibility index among cultivars was signifi cant under early and terminal stress conditions, but not under mid-str ess conditions. Yield potential and stability were not correlated for the different drought-stress conditions. Longer grain-filling period, increased number of kernels per spike and limited spike number per m(2 ) can be used as selection criteria for sustainable yield in water-lim ited environments.