Comparison between rice (Oryza sativa L.) cultivars for competitiveness against barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.)

The aim of this research was to compare seven cultivars and three lines of rice (Oryza sativa L.) for competitiveness against barnyardgrass (Echinochloa crus-galli). A filed experiment was conducted in 2007 growing season in Mazandaran province، North of Iran. In this experiment، seven rice cultivars (Khazar، Sepidrood، Nemat، Dorfak، Fajr، Shiroodi، and Dailamani) and three lines (Line 830، Line 841 and Line 843) were sown with and without barnyardgrass. Layout of the experiment was a factorial design with four randomized complete blocks. Each cultivar or line was planted at its own optimum density، while density of barnyardgrass was 20 plants per square meter. Results showed that in all rice cultivars and lines tested، yield and its components were significantly reduced in the presence of barnyardgrass. Moreover، there was a significant difference among rice cultivars and lines in competitive index (CI) and ability withstand competition (AWC). Line 843 had minimum yield reduction percentage (18%)، highest CI (2. 43) and AWC (82)، while Khazar cultivar had maximum yield reduction percentage (50. 65%)، lowest CI (0. 32) and AWC (49. 5%). Correlation analysis confirmed that there was a positive significant correlation among rice yield، CI and AWC. The Cluster Analysis showed that all cultivars and lines fell into four different clusters. First، khazar cultivar had high yield potential under weed-free conditions، but low CI and AWC. Second، line 843 had high yield potential under weed-free conditions، CI and AWC. Third، shiroodi cultivar had high yield potential under weed-free conditions، and low CI but high AWC and forth other lines and cultivars had low CI and AWC. Based on this experiment، line 843 was the most competitive Line and khazar cultivar was the least competitive cultivar against barnyardgrass.