Allelopathic effect of canola on annual ryegrass

Canola is a leading winter grain crop in Australia but declining yields due to the impacts of weeds and resistances to herbicides is a significant issue for Australian cropping systems. Although weed control herbicide options are available for canola, the prospects of herbicide resistance necessitate considering alternative options such as the allelopathic potential of canola for weed suppression. To assess the allelopathic prospects of canola, a laboratory-based root exudates bioassay was conducted using ECAM (Equal-Compartment-Agar Method). The allelopathic effects of different growth duration (0, 3, 5, 7, 9, 11, 13, and 15 days) and density (15, 30, 45, and 60 seeds/beaker) of canola (var. Ag-Spectrum) against annual ryegrass (as a test species) were investigated. During harvest the inhibited root length and diameter of ryegrass was measured. The experiment was designed as a randomised complete block with three replications and conducted under control conditions. Results showed that canola reduced the root length of ryegrass for 3'9days, and at a density of 60 seeds/beaker was most inhibitory, suggesting that root exudates of canola are correlated with seedling density. Although, the root surface area was not influenced by density, it was significantly influenced by growth duration. Root surfacearea of canola was noticeably inhibited during 3'9 days. The effect of retention of canola root exudates prior to ryegrass sowing was also evaluated under the same experimental conditions. Canola was grown for 0, 3, 5, 7, 9, 11, 13 and 15 days with 60 seeds/beakerusing ECAM, then canola seedlings were removed from the beakers before 15 pre-germinated ryegrass seeds were transplanted into each beaker. There was a significance difference between ryegrass grown with or without prior canola. Increasing growth durationof canola increased the inhibition effect up to 9 days butwith growing time beyond this period there was no further noticeable inhibition.