Yield Formation in Mediterranean durum wheats under two contrasting water regimes based on path-coefficient analysis

The components of grain yield are altered by adverse growing conditions as the effects of certain environmental factors on crop growth and yield differ depending upon the developmental stages when these conditions occur. Path-coefficient analysis was used to investigate the main processes influencing grain yield and its formation under Mediterranean conditions. Twenty-five durum wheat genotypes, consisting of four Spanish commercial varieties and 21 inbred lines from the ICARDA durum wheat breeding program, were grown during 1997 and 1998 under both rainfed and irrigated conditions in southern Spain. {P}ath-coefficient analysis revealed that under favourable conditions grain yield depended in equal proportion on the three primary yield components (i.e. spikes m(-2), grains spike(-1), and mean grain weight), whereas in the rainfed experiments, variations in grain yield were due mainly to spikes m(-2) and to a lesser extent to grains spike(-1). Compensatory effects were almost absent under irrigated treatments; however, under water shortage, spikes m(-2) exerted a negative influence on grain spike(-1) due mainly to a negative interrelationship between tiller production and apical development. These compensatory effects could partially explain the restricted success in durum wheat breeding observed in water-limited environments of the Mediterranean region. Under rainfed conditions the number of spikes m(-2) depended mainly on the ability for tiller production, whereas in the irrigated experiments the final number of spikes was determined mostly by tiller survival.