The impact of plant breeding on the grain yeild and competitive ability of wheat in Australia

Fourteen wheat (Triticum aestivum L.) cultivars released to Australian growers over the last century were examined to determine the impact of crop breeding on competitive ability with weeds. In 1999 and 2000 the weed used in the field study was annual ryegrass (Lolium rigidum Gaud.) and in 2001 oats (Avena sativa cv. Marloo) was the weedy competitor. In 2 out of 3 years (1999 and 2001), when Puccinia recondita (leaf rust) infection was not a problem, there were consistent trends for improvement in yielding ability through breeding effort over time. In these 2 seasons the yielding ability of wheat increased by around 15 kg/ha.year as compared with a yield increase of only 4.7 kg/ha.year in 2000 due to a heavy P. recondita infection. In 1999 and 2000, when annual ryegrass was used as the weedy competitor, there was no systematic trend for changes in crop yield loss with time (r = 0.47 in 1999; r = 0.08 in 2000, P > 0.05). However, in 2001, when oat was used as the weed, there was a significant positive linear relationship (r = 0.81, P < 0.01) between the year of cultivar release and crop yield loss, indicating inferior competitive ability of the modern cultivars. Old cultivars such as Nabawa not only provided superior weed suppression, they were also more tolerant of weeds as indicated by the smaller yield loss. Plant height appeared to be an important contributor to the superior competitiveness of the standard height, older cultivars. Other morphological traits contributing to superior competitive ability included greater leaf length and width, light interception, and flag leaf length. To improve the competitive ability of modern wheats without compromising their yielding ability, morphological traits that enhance early crop vigour (size of leaf 1 and 2) and light interception without affecting harvest index may need to be incorporated from carefully selected germplasm.The impact of plant breeding on the grain yield and competitive ability of wheat in Australia R. K. Vandeleur and G. S. Gil