GRAIN-YIELD AND WATER-USE EFFICIENCY OF EARLY-MATURING WHEAT IN LOW RAINFALL MEDITERRANEAN ENVIRONMENTS

Wheat cultivars with very early maturities appropriate for late sowing s in low-rainfall (<325 mm) short-season environments are currently un available to wheat growers in the eastern margin of the cropping regio n of Western Australia. A demonstration that very early-maturing genot ypes can out-perform current commercial cultivars would open new oppor tunities for breeding programs to select very early-maturing, high- an d stable-yielding: cultivars for these environments. Six field experim ents were conducted over 4 seasons at 2 low-rainfall sites in Western Australia to investigate crop growth, grain yield, and water use effic iency of very early-maturing genotypes compared with current commercia l cultivars when sown after 1 June. Very early-maturing genotypes reac hed anthesis up to 24 days (328 degree-days) earlier than the current cultivars, produced less leaves, had similar yields and dry matter, an d maintained high water use efficiencies. On average across seasons an d locations the very early-maturing genotypes (W87-022-511, W87-114-54 9, W87-410-509) yielded more than the later maturing cultivars Gamenya and Spear (190 v. 160 g/m(2)) but they were similar to the early-matu ring commercial cultivars Kulin and Wilgoyne (191 g/m(2)). Very early- maturing genotypes generally had a higher han;est index and produced f ewer spikelets, but heavier and more grains, than Kulin and Wilgoyne. There were only small differences in total water use between very earl y-maturing genotypes and commercial cultivars; however, very early-mat uring genotypes used less water in the pre-anthesis period and more wa ter in the post-anthesis period than the later maturing genotypes, and hence, experienced less water deficit during the grain-filling period . This study indicates that there is a role for very early-maturing ge notypes in low-rainfall short-season environments, when the first autu mn rains arrive late (after 1 June).