Nimesha Fernando1, Bhagirath Singh. Chauhan2, Saman Seneweera3, Mani Naiker1, Singarayer K. Florentine1
1 School of Applied and Biomedical Sciences, Faculty of Science and Technology, Federation University, Mount Helen Campus, Ballarat, VIC 3350, Australia
2 Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Gatton, Queensland 4343, Australia
3 Centre for Crop Health, University of Southern Queensland, Toowoomba QLD 4350, Australia
Annual ryegrass (Lolium rigidum Gaud.), a troublesome weed in winter cropping systems is likely to increase competitiveness with major crops under climate change. To test this hypothesis, we grew wheat (Triticum aestivum L. cv. Yitpi) and annual ryegrass to measure the level of competition and competition-mediated plant defence responses. The experimental design was factorial with two [CO2] (a[CO2] vs e[CO2]), two watering levels (80% field capacity and drought during DC 60; heading stage) and two competition treatments (wheat only; W only, wheat × ryegrass; W × R) with eight replicates. In the W × R treatment, wheat (by 39%) and ryegrass (by 105%) produced higher biomass under e[CO2] compared to a[CO2]. Total biomass of wheat grown in W × R, increased by 31% at DC 90 compared to DC 60 under a[CO2] and wheat biomass increased only by 5% at DC 90 compared to DC 60 under e[CO2]. Ryegrass biomass increased at DC 90 compared to DC 60 under both a[CO2] (by 62%) and under e[CO2] (by 157%). Total antioxidant capacity (TAC) of wheat grains at maturity was higher in all the experimental conditions under e[CO2] than at a[CO2] except wheat grown in W × R under drought conditions. These results confirm that wheat can compete better with ryegrass during the vegetative growth under e[CO2]. However, during reproductive development, ryegrass showed greater competition with wheat under e[CO2] than at a[CO2]. Further, these findings suggest that additional management strategies to control ryegrass under future climate change will be required.