Path Analysis of Rice (Oryza sativa L.) Grain Yield and its Related Components in Competition with Barnyard Grass [Echinochloa crus-galli (L.) P. Beauv.]

One component of integrated weed management is use of cultivars with high competitive ability against weeds. Balance between competitiveness and productivity of rice under condition of presence or absence of weeds, is complicated the breeding of rice cultivars to increase competitiveness against weeds. Path coefficient analysis has been widely used in crop breeding to determine the nature of relationships between the grain yield (GY) and its contributing components. To study the weed-suppressive ability by rice, an experimental was conducted in a randomized complete block design with four replications in Chprsr, Tonekabon Rice Research Station at 2009. The experimental treatments include seven varieties (Daylamani, Khazar, Sepeedrud, Neamat, Dorfak, Fajr and Shiroodi) and three lines (830, 841 and 843) of rice that were cultured in the presence of barnyard grass. The results of path analysis showed ability withstands competition (AWC), thousand grain weight (THGW), fertile tiller number m-2 (FT), filled grain number panicle-1 (FG) and competitive index (CI) as the first-order variables for GY. The traits such as specific leaf area of rice at 25 days after transplanting (Rsla25), ear length (EL), Filled grain percentage (FGP), specific leaf area of rice at heading stage (RslaHD) were as the second-order variables for GY and influenced positively this response variable. Dry weight of barnyard grass biomass was negatively correlated with CI and RslaHD. However, these traits have a positive effect on grain yield, but fertile tiller number and specific leaf area at heading stage are measurable before maturity of grain. Thus, select of cultivar with high grain yield is possible before heading of grain, through these two traits. The variety of Shiroodi and line of 843 with highest value of specific leaf area at 25 days after transplanting and heading stage, high ability withstands competition and competitive index have a high capacity to compete with barnyard grass and can be considered as a suitable cultivar in selection processes and are also used as crosses parents.