The damaging effects of weeds are significant in that losses in wheat globally range from 8 to 23%. Herbicides are the dominant choice for weed management. However, 497 unique cases of herbicide-resistant weeds have been identified with resistance to 23 of the 26 known different herbicide modes of action2. Pressure to maintain the longevity of new and existing chemistries, and reduce the cost of herbicide management to increase grower profitability has emphasized the urgent need to implement alternative protection strategies.

Crop competition is one such protection strategy. Sowing a weed-competitive cultivar is easily implemented, is readily combined with other protection strategies, and moreover is both low cost and low risk. Unfortunately few competitive wheat cultivars have been released commercially and few competitive traits established for use in breeding.

Early vigour represents more rapid leaf area development through wide leaves and greater biomass at stem elongation. Greater vigour is a common mechanism in competing in natural plant communities, and provides an equally effective ideotype to improve crop competition in managed farming systems: early shading of the soil to reduce radiation for the growth of competing weed seedlings, and reduced light to inhibit weed seed germination.

In our research we have introduced early vigour from overseas wheat germplasm into elite Australian varieties together with dwarfing genes Rht12, Rht13 and Rht18 through traditional breeding. Over 6000 backcross- and topcross lines have been developed for release to breeding companies and to study crop-weed competition in trait validation, genotype × management interaction, and high throughput phenotyping methods.

We will present results on 150+ developed competitive lines and commercial Australian cultivars grown with and without weed competition using weed mimics oat, barley, canola and winter ryegrass either sown together with the wheat or oversown shallower than the wheat.

Experiments have been grown over four seasons in irrigated and rainfed environments, representing a total of 10 siteyears. Preliminary data reveals significant and repeatable genetic variation in wheat suppressive and tolerance abilities to the weed mimics.