AN INVESTIGATION OF THE GRAIN-YIELD ADAPTATION OF ADVANCED CIMMYT WHEAT LINES TO WATER-STRESS ENVIRONMENTS IN QUEENSLAND .1. CROP PHYSIOLOGICAL ANALYSIS

Wheat improvement in Australia has made extensive use of germplasm dev eloped by the International Maize and Wheat Improvement Center (CIMMYT ). The opportunity for further yield improvement in Queensland was inv estigated by comparing CIMMYT lines and Queensland cultivars in irriga ted and dryland environments at three locations. CIMMYT lines were ide ntified, with greater than 20% yield advantage in individual environme nts and between 15 and 20% yield advantage over the six environments. The line mean repeatability for yield was moderate (0.492), with the v ariance component for line by environment (L x E) interaction 4.2 time s that for lines. Therefore, while the CIMMYT lines expressed consider able L x E interaction, there was scope for further yield improvement. The water stress differential between the irrigated and dryland envir onments at the three locations strongly influenced L x E interaction f or grain yield. Pre-anthesis water stress generated more L x E interac tion for grain yield than post-anthesis stress. At the two locations w here pre-anthesis water stress was severe in the dryland environment, there was no association (P > 0.05) between yield under irrigated and dryland conditions. However, at the location where there was little pr e-anthesis stress and a degree of post-anthesis stress there was a str ong association (P < 0.01) between yield under irrigated and dryland c onditions. Grain yield was positively associated with the yield compon ent grain number per unit area in all environments. Grain weight showe d little L x E interaction across environments and the majority of L x E interaction for grain yield resulted from L x E interaction associa ted with grain number per unit area. Grain number per unit area was po sitively associated with the component grains per fertile tiller but n ot tiller number per unit area. Grains per fertile tiller was in turn positively associated with total dry matter at anthesis; however, ther e was no direct association between total dry matter at anthesis and g rain number per unit area. There was a weak association between days t o anthesis and grain yield in four of the six environments.