Effect of Height on the Competitive Ability of Wheat with Oats

Competitive ability of wheat is influenced by a range of attributes such as plant height, tiller number, and light interception. This study focused on the effect of plant height on weed competitiveness of a set of near-isogenic wheat lines (NILs). The set included seven bread wheat (Triticum aestivium L.) and six durum wheat (T. turgidum L.) cultivars, each having a semidwarf and tall near-isogenic line. These lines were examined in field experiments conducted over two growing seasons. Oats (Avena sativa 'Marloo') were used as a weed mimic and sown with the wheat and various plant traits were recorded. The tall NILs were more competitive than the corresponding semidwarf lines, having consistently lower yield losses in both years with differences between NILs ranging from 3 to 10% for bread wheat and 10 to 17% for durum wheat. Greater suppression of oat seed production was observed during 2003, tall NILs reduced oat seed production by 26% (P < 0.01) in bread wheat and 41% (P < 0.001) in durum wheat. Increasing plant height improved bread and durum wheat's ability to tolerate and suppress oats. In addition to plant height, traits associated with early vigor such as length and width of leaves 1 and 2, early plant biomass and leaf area index (LAI) were also shown to have a significant influence on crop yield loss and weed suppression, but these correlations were not consistent across both years. The results suggest that selection for high early vigor could reduce the negative effect of reduced plant height on weed competitive ability.