Effect of Redroot Pigweed (Amaranthus retroflexus) on Growth Indices and Yield of Red Kidney Bean (Phaseolus vulgaris) Cultivars

In order to identify red kidney bean cultivars with high competitive ability a set of experiment was conducted at Research Farm of University College of Agriculture and Natural Recourses University of Tehran (Karaj) in 2006 and 2007, to evaluate the competition effect of red root pigweed on growth indexes, seed yield and yield components of red bean cultivars. In 2006 different densities of pigweed including 0, 4, 8, 16 and 32 plant/m2 and three cultivars of red bean (Akhtar, Sayyad and Line D81083) were used in a factorial experiment with complete randomized block design. In 2007, cultivars Gholi and mixed cropping of cultivar Gholi and Aktar were added to the first year treatments. Results indicated that the cv. Gholi and Sayyad had more leaf area index and crop growth rate than cv. Akhtar and Line D81083. The leaf area index and growth rate of pigweed in competition with the red bean cultivars of Gholi and Sayyad were lesser than that of cv. Akhtar and Line D81083 that indicate more competitive ability of cv. Gholi and Sayyad.The results indicated that in both years, the effect of pigweed density on bean seed yield and pod number per plant was significant. In 2007, the pigweed density of 32 plants/m2, reduced seed yield of cultivar Akhtar, Line D81083, Gholi, Sayyad and mixed cropping of Gholi and Akhtar, 72.5, 80.5, 49.8, 60.35 and 58.1 %, respectively. Based on the yield loss model coefficients (a & m) red kidney bean cultivars of Gholi and Sayyad had the most competitive ability and Line D81083 had the least competitive ability against the redroot pigweed. In 2007, redroot pigweed had more competitive ability against the all bean cultivars than 2006.