Density-dependent wheat allelopathy: Effectiveness for weed control, associated root interaction and morphology changes

A laboratory-based root exudates bioassay was conducted to assess the density-dependent allelopathic potential of wheat against annual ryegrass(Lolium rigidum Gaud.) Results showed that increasing the density of wheat plants significantly inhibited the seedling growth of annual ryegrass. Root andshoot dry biomasses of annual ryegrass were reduced by up to 80% and 70%, respectively. At lower wheat densities the dominant root diameter of annual ryegrass(>50% of roots) was between 0.000 and 0.018 mm.As wheat density increased the diameter of annual ryegrass fibrous roots was increased as well and gradually dominated by the root diameter between 0.018 and 0.270 mm (>50% of roots). Total allelochemical level in the wheat root exudates was linearly correlated withwheat density (r2 = 0.988**). These results suggest that strong allelopathic effects from allelochemicals exuded from wheat plant roots might have contributed to increased wheat competitiveness at high densities and ultimately led to the suppression of annual ryegrass growth and development.