The effect of annual ryegrass (Lolium rigidum) interference on the growth of four common Australian crop species

Lolium rigidum (annual ryegrass ' ARG) is a ubiquitous weed of southern Australia infesting the majority of winter crops. This paper considers the role of allelopathy in the interactions between ARG and the associated crop species to improve the understanding of why ARG is such a successful weed. Four crop species, i.e. lupin, barley, wheat and canola, were exposed to root exudates of ARG to determine the extent of variation in growth responses. At high ARG densities, root lengths of all crop species were significantly inhibited. Increasing the duration of ARG growth in the agar medium before introduction of the crop species further reduced crop growth. However growth responses differed between crop species. Canola was the most affected by ARG interference (67.5% root inhibition) followed in declining order by wheat (56.6%), barley (37% ) and lupin (31.1% root inhibition,). Activated carbon and removal of ARG plants prior to crop sowing were used to verify the presence of putative inhibitory chemicals.