ARS | Publication request: Identifying soybean traits of interest for weed competition

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2011
Publication Date: November 1, 2011
Citation: Place, G.T., Reberg-Horton, S.C., Dickey, D.A., Carter Jr, T.E. 2011. Identifying soybean traits of interest for weed competition. Crop Science. Vol. 51, pp. 2642-2654.

Interpretive Summary: Currently, over 90% of soybean hectarage in the USA utilizes transgenic herbicide resistance technology. The hectarage of organic, herbicide-free soybean, by contrast, is small but increasing rapidly. The profit margin for organic soybeans can be substantial, but farmers making the transition to organic soybean production cite weed management as a top challenge. The utilization of more competitive soybean cultivars may be a solution. However, at present there is a dearth of information which can be used to guide soybean breeding in this area. Identification of competitive traits would allow breeders to begin the process of development of weed resistant varieties. We investigated the weed competitiveness of 27 soybean genotypes that were selected to represent diversity for an array of traits, including seed size, petiole length, leaflet size, and main stem height. Our main objectives were to 1) identify differences in weed competitive ability among these genotypes and 2) determine the relation of genetic morphological traits to the overall competitive ability of a genotype.

Technical Abstract: Organic soybean producers rely on a variety of tactics for weed management. The use of soybean cultivars with enhanced ability to compete with weeds may increase weed control. Our objective was to identify genetic traits that may enhance soybean’s competitive ability to suppress weeds. Experimental design was a split-split plot with sets of contrasting soybean genotypes assigned to the main plots, individual genotypes assigned to subplots and weedy and weed-free sub-sub plots stripped across blocks for side by side comparison of treatments in weedy and weed-free conditions. Differences in weed biomass were detected among genotypes in both years at seven weeks after emergence. Narrow-leaflet small-seeded natto types were generally poor competitors with weeds. Cultivars released as forage types did not have a consistent advantage over the control. Larger-seeded tofu genotypes were also variable in weed suppressive ability. However, N04-8906, the genotype with the greatest 100-seed weight in this study (24 g), stood out as being among the best for weed suppression, soybean biomass accumulation, ground cover at three weeks, and early season plant height. Optimum models from multiple regression showed seed size to be the most significant trait measured in overall genotype competitive ability in both years.