Variation of weed-suppressing potential of Vietnamese rice cultivars against barnyardgrass (Echinochloa crus-galli) in laboratory, greenhouse and field screenings

A total of 73 different varietal groups and cultivars of Vietnamese rice (Oryza sativa L.) were evaluated for the allelopathic potential on barnyardgrass (Echinochloa crus-galli) in laboratory, greenhouse and field screenings. In a bioassay, Y1, U17, Nep Thom and Lua Huong, cultivars showed the highest weed-suppressing ability against the length of shoot and root of barnyardgrass. Y-1, Nhi Uu and Khau Van exerted significant inhibitory effects in greenhouse screening. In the field study, Phuc Tien obtained the highest weed-suppressing potential. The allelopathic activity of Vietnamese rice showed cultivar-dependence and varietal group-dependence, of which hybrid group cultivars (H) showed the highest inhibition, followed by the local non-sticky cultivars (LNS), foreign (F), traditional sticky (TS), and traditional upland sticky (TUS), while the least were the local upland non-sticky (LUNS) cultivars. The inhibition exerted in both bioassay and greenhouse was lower than the observed weed suppression in the field by 15–20%; however, rice cultivars against the growth of barnyardgrass in greenhouse screening showed more correlation to the results obtained in the field than that of the laboratory, but both laboratory and greenhouse screenings may arduously reflect the actual weed-suppressing ability of rice exhibited in the field. The obtained data might be useful for the enhancement of the weed-suppressing ability of rice in this country.