Annual ryegrass (Lolium rigidum Gaud) competition altered wheat grain quality: A study under elevated atmospheric CO2 levels and drought conditions

Annual ryegrass is one of the most serious, costly weeds of winter cropping systems in Australia. To determine whether its competition-mediated plant defence mechanisms effect on wheat grain quality, wheat (cv. Yitpi) and annual ryegrass were grown under two levels of CO2 (400 ppm; (a[CO2]) vs 700 ppm; (e[CO2]), two levels of water (well-watered vs drought) and two types of competition (wheat only; (W), and wheat × annual ryegrass; (W × R) with four replicates. The competition × [CO2] interaction had a significant effect on wheat grain protein content, where it was increased in W × R under both e[CO2] (+17%) and a[CO2] (+21%). Grain yield, total grain reducing power and phenolic content were significantly affected by [CO2] × drought × competition. In a summary, annual ryegrass competition significantly altered the wheat grain quality under both [CO2] levels (depending on the soil water level), while also decreasing the grain yield.