evaluating inhibitory potential of rice cultivars (oryza sativa l.) root exudates on characteristics of barnyardgrass (echinochloa crus-galli) weed

this experiment was conducted to screening phenolic acids in root exudates of three rice cultivars (neda, taichung and sepidrood) by high performance liquid chromatography (hplc) method and to evaluate allelopathic potential of these cultivars on growth characteristics of barnyardgrass weed. the experiment was arranged in factorial based on completely randomized design with four replications in greenhouse and laboratory conditions at sari agricultural sciences and natural resources university during 2007. the results of anova indicated that all treatments and interactions had significant effect at 0.01 levels on all studied traits. in terms of more studied traits, taichung (root exudates) had the highest amounts compared to other cultivars. accordingly, taichung by 40.60% and sepidrood by 0.60% had the highest and lowest inhibitory on root lengths of barnyardgrass, respectively. in terms of dry weights, taichung and sepidrood had the highest and minimum effect with 29.60 and 2.60 inhibitory percentages, respectively. root exudates of thaichung with 50.90% and 31.90% had the highest inhibitory effects on germination rate and percentage of barnyardgrass seeds, respectively. in terms of physiological traits such as chlorophyll and nitrogen contents the highest amount of inhibition were related to neda (with 58.20% and 43.80%, respectively) and the lowest amounts were recorded for sepidrood (with 1.70% and 11.30%, respectively). root exudates of all cultivars were also analyzed by hplc method. the results showed that the highest phenolic contents (6.085 mg/l) were related to root exudates of taichung and the lowest amounts (0.201) were belonged to neda.