Evaluation of response of Red bean cultivars with two different growth habits on weed competition

Common bean (Phaseolus vulgaris L.) has been considered as an important source of protein and calorie. This plant plays an important role in supplying the human's protein. Bean crop is highly susceptible to weeds due to low growth rate early in the growing season. Therefore, competition with weeds causes a significant reduction in grain yield at the end of the growing season. Weed competition is a kind of non-living stress, which affects plant yield. Weeds and crops are always competing for obtaining nutrients, water, light and space (CO2). Examining the effect of weed interference time during the critical period provides valuable information regarding the physiological outcome of competition between weeds and crops. Red bean cultivars, with different morphological and genetic characteristics, show different responses in the presence of weeds, which may ultimately result in possible difference in yield. Unlimited growth genotypes showed higher competitive ability than those with limited growth genotypes. However, there are contradictory reports about the effect of growth habits on competitive ability. Measurement of growth indices is necessary to study the competitive ability of species during the growth period. The aim of this study was to investigate the response of some morphophysiological traits of three red bean cultivars with two different growth habits to weeds. 

A field experiment was conducted to investigate the morphological and physiological characteristics of three red bean cultivars with two different growth habits (semi erect and erect) under weed competition in the experimental research station at the Faculty of Agriculture, University of Ilam, Iran. The experiment was conducted as factorial based on a randomized complete block design with two factors including: cultivars (Sayad, Derakhshan and line D81083) and weed competition at two levels (weed free and infested during the growing season) with three replications. The traits related to red bean such as plant height, biomass, chlorophyll a, b and total chlorophyll, anthocyanin and carotenoid at the stages V4, R6, R7 and grain yield and yield components were measured at physiological maturation stage. The importance value of weed (IVW) was measured in two stages V4 and R9. Competitive index (CI) was used to evaluate the competitive ability of common bean varieties against weeds. The software of SPSS 22, SAS 9.4 and Excel 2013 were used for test normality, data analysis and drawing charts, respectively. Means comparison was performed by the least significant difference test (LSD). 

 Convolvulus arvensis had the highest importance value of weed (IVW) index from the beginning of growth until stage V4. At stage R9, the Purtulaca oleracea and Amaranthus retroflaxus had the highest values of IVW by 27.33% and 21.92%, respectively. The latter are dominant species in the western regions of the country. The results showed that cultivar type and weed competition had significant effects on the bean crop height at all studied stages. In addition, the effect of interaction between cultivar and weed competition was significant on leaf area (LA) and height at V4 and R7 stages, respectively. At all stages, traits such as height and leaf area of red bean cultivars were significantly decreased owing to weed competition compared to the weed control. Line D81083 and Sayad had the highest and lowest leaf area in competition with weeds during all stages, respectively. The effect of interaction between cultivar and weed competition was significant on grain yield and number of pods per plant. Line D81083 and Derakhshan cultivars had the highest and lowest seed yield in competition with weeds, respectively. Line D81083 had the most competitive index among the cultivars. There were no significant differences between Sayad and Derakhshan in all studied traits. Weed competition had a significant effect on chlorophyll a, b and total chlorophyll at V4 and R7 stages. Anthocyanin and carotenoids were not affected by the treatments at V4 stage. Overall, chlorophyll a, b and total chlorophyll were significantly increased in the absence of weeds. The effect of differences in anthocyanin value was significant based on the cultivar and weed presence, while carotenoid content was only affected by the cultivar type at R7 stage.

The present study showed that use of line D81083 could increase grain yield of red bean up to 2-fold under weed free conditions compared to crop-weed interference conditions. Line D81083 had the highest grain yield, pod per plant, 100-grain weight, and competition index when full-season weed competition occurred.