Allelopathic assessment of annual ryegrass (Lolium rigidum): Bioassays

A laboratory-based root exudates bioassay was conducted to assess the allelopathic potential of annual ryegrass against wheat using the equal-compartment-agar method. The allelopathic effects of different growing times of ryegrass (2, 4, 6, 8, 11 and 15 days) was investigated on wheat. Results indicated that co-growth of annual ryegrass and wheat reduced the root and shoot length of wheat. Ryegrass growth for 6'8 days was most inhibitory to wheat root growth. Increasing ryegrass density beyond 20 plants per beaker did not increase the allelopathic activity of annual ryegrass. To validate the allelopathic effects between the ryegrass and wheat, activated charcoal was added to the growth medium (2% v/v), it increased the inhibition of wheat root and shoot length. Thus, the inhibitory effect of annual ryegrass on wheat root and shoot length was chemically directed through its root exudates, inhibition was greater on wheat roots than on wheat shoots.The allelopathic effect of ryegrass root exudates was evaluated on root and shoot growth of four wheat cultivars, (WW14192, Ventura, Sunco and Janz). The allelopathic effect of ryegrass differed on root and shoot growth of wheat cultivars, the greatest effect was on root and shoot growth of cultivar WW14192. However, the trends were similar for all cultivars.