Trends in yielding ability and weed competitiveness of Australian wheat cultivars

Abstract

Wheat breeding in Australia has undoubtedly resulted in large improvements in grain yield. This has been partly achieved through reduced plant stature, which may have compromised the ability of modern cultivars to compete with weeds. Fourteen cultivars released to Australian growers from 1860 to 1994, were grown in a field study at Roseworthy to determine whether there has been a systematic decline in weed competitive ability of wheat varieties over time. Oats (Cv. Marloo) were used as the weedy competitor in this study and were sown with the wheat to create paired weedy and weed-free plots. A regression analysis of spatially adjusted mean wheat yield against the number of years since 1860 indicated a rate of increase of 16.6 kg/ha/year in yielding ability in the absence of weeds. The recently released cultivars, Spear, Excalibur and Frame suffered a greater yield loss due to weed competition but the actual yields in the presence of oats were still greater than that for the majority of older cultivars, except Gluyas Early, Nabawa and Gabo. Increased yield loss due to weed competition was associated with reduced plant height and light interception at early stem elongation (P<0.05). The newer varieties were consistently poor in suppressing weed growth and seed production. This decline in weed suppression was correlated with reduced early vigour (leaf 2 width; P<0.05) and plant height (P<0.06). The results clearly indicate that the improvements through plant breeding have increased the yielding ability of cultivars, but their ability to suppress weeds has been reduced. Competitive wheat cultivars have the potential to make a significant contribution to weed management but improvements in competitive ability need to be achieved through the incorporation of traits that do not compromise yielding ability.