Evaluation of grain yield and its components in durum wheat under Mediterranean conditions:: An ontogenic approach

Grain yield of durum wheat (Triticum turgidum L. var. durum) under Mediterranean conditions is frequently limited by both high temperature and drought during grain growth. Path coefficient analyses, based on an ontogenetic diagram, were conducted to study grain yield formation under different temperature and moisture regimes across Spain. Six ICARDA-CIMMYT inbred lines and four Spanish commercial cultivars were grown during 1998 and 1999 at two temperature regimes (cool and warm) and under both rainfed and irrigated conditions. Path coefficient analysis revealed that grain yield under cooler conditions was mostly determined by kernel weight, whereas the number of spikes per square meter predominantly influenced grain production in the warmer environments. The number of kernels per spike had a significant contribution to grain yield, especially under drought stress conditions. These associations do not clearly appear in the simple correlation analysis. Compensatory effects among yield components were almost absent in the cooler environments, probably due to the relative availability of water and N during the critical phases of plant development. Contrarily, under warmer conditions, negative effects of the number of spikes per square meter were registered on both the number of kernels per spike and kernel weight. Path analysis appears to be a useful tool for understanding grain yield formation and provides valuable additional information for improving grain yield via selection for its yield components.