Allelopathic Potentials of Eight Barley Cultivars on Brassica jucea (L) Czern. and Setaria viridis (L) p. Beauv.

The allelopathic potential of the foliage tissues of eight barley cultivars was investigated using seedlings bioassays of Indian brown mustard (Brassica juncea) and green foxtail (Setaria viridis) as typical broadleaf and grass weeds of the croplands. The correlations of allelochemical compounds with seed germination of weeds were determined. The barley cultivars used were Jackson, Bronco, CDC Dolly, B1602, Harrington, UNA80, Stander, and TR251. Three dilutions of the extracts of each barley cultivar (20, 10 and 5 g/L) plus deionized distilled water, as a control, were assayed on the target weeds. The effects of barley cultivars and extract concentrations on seed germination and radicle and shoot lengths of the target weed seeds were highly significant (P<0.001). By increasing the concentration of the allelopathic extracts, the percent germination, radicle and shoot lengths of both target plants seedlings decreased. Seed germination and seedling growth of B. juncea were more sensitive than those of S. viridis. Relative to the germination inhibition of target weed seeds in comparison to the untreated control, the selected barley cultivars were categorized as being highly allelopathic, moderately allelopathic and of low allelopathic potential. Among the phenolic compounds detected, the cumulative effect of four small-quantity-compounds (vanillic, chlorogenic, p-coumaric, and ferulic acids) on average weed germination was very high (R2 = 0.83), with B. juncea it was high (R2 = 0.70) and with S. viridis it was very low (R2 = 0.15). The two high concentration phenolic compounds of protocatechuic and p-hydroxybenzoic acid, when accumulated with the small-quantity phenolic compounds of barley cultivars, reduced the weed seeds germination correlation to r=- 0.11.