Field evaluation of Australian commercial wheat genotypes for competitive traits and weed suppression

In 2014 to 2016, replicated field trials were performed to evaluate mechanisms of weed suppression in diverse Australian wheat genotypes in moderate to low rainfall zones at Wagga Wagga and Condobolin NSW, respectively, in commercially managed paddocks. In 2014, a total of 11 winter wheat cultivars (Triticum aestivum L.) representing four major breeding family lines grown in Australia were evaluated; in 2015 and 2016, 13 cultivars were assessed including the heritage cultivar Federation. At each site, crop and weed growth were monitored at various phenological stages including early season, vegetative, grain-filling, harvest and post-harvest to the crop.
Significant differences between wheat cultivar and location were observed for crop biomass, early vigour, leaf area index (LAI), weed number, weed biomass, canopy architecture and yield in each year the experiment was conducted. Differences in weed suppression were largely impacted by crop architecture and phenology early in the growing season, particularly leaf shape and the ability to achieve early canopy closure. Cultivar competitive traits were also influenced by both genotype and environmental factors, as shown by clear differences in cultivar performance, yield and weed suppression among both locations. Cultivars Condo and Espada were superior performers in terms of weed suppression and yielding potential in both locations and all years.
Our results were replicated over multiple locations and years and clearly suggest that establishment of competitive wheat cultivars can result in effective suppression of weed growth (up to 90% or greater) in the absence of post-emergent herbicides. This suggests that weed suppression may be associated with cultivar competitive ability and/or allelopathy. In addition, the choice of wheat cultivars for desired yield and weed suppression impacts the subsequent ability of the crop to successfully interfere with weed growth and can prevent future weed propagules from entering the weed seedbank. Therefore, the choice of wheat cultivar can provide cost-effective and sustainable weed management and is useful tool, in addition to the use of pre-emergence herbicides.