Screening of soybean for pendimethalin herbicide induced stem damage

Field-grown soybean [Glycine max (L.) Merr.] have exhibited stem breakage, lodging, reduced nodulation, and enlarged root tips and hypocotyls (brittle bean syndrome) after treatment with pendimethalin herbicide [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitro-benzenamine]. Greenhouse and held research was conducted in 1993 and 1994 to develop and evaluate screening systems (herbicide rates, experimental units, and rating methods) to quantify soybean susceptibility to brittle bean syndrome. Both field and greenhouse experiments resulted in injury to soybean plants consistent with pendimethalin-induced stem damage previously observed in the held. Greenhouse evaluation of cultivars and breeding lines detected significant differences among entries for stem breakage with pendimethalin rates at 0.56, 1.68, and 2.80 kg ha(-1). Significant differences among entries for stem breakage were also observed in field trials. Rank correlations among entries for stem breakage at the 1.12 kg ha(-1) field rate vs. the 1.68 or 2.80 kg ha(-1) greenhouse rates of pendimethalin were 0.7** and 0.8**, respectively. Although the field and greenhouse evaluations were not in complete agreement, the relative performance of the entries provided evidence that greenhouse screening is an effective tool to characterize genetic variation in soybean for resistance to brittle bean syndrome.