SCREENING OF SOYBEAN FOR PENDIMETHALIN HERBICIDE INDUCED STEM DAMAGE

Field-grown soybean [Glycine max (L.) Merr.] have exhibited stem break age, lodging, reduced nodulation, and enlarged root tips and hypocotyl s (brittle bean syndrome) after treatment with pendimethalin herbicide thylpropyl)-3,4-dimethyl-2,6-dinitro-benzenamine]. Greenhouse and hel d research was conducted in 1993 and 1994 to develop and evaluate scre ening systems (herbicide rates, experimental units, and rating methods ) to quantify soybean susceptibility to brittle bean syndrome. Both fi eld and greenhouse experiments resulted in injury to soybean plants co nsistent with pendimethalin-induced stem damage previously observed in the held. Greenhouse evaluation of cultivars and breeding lines detec ted significant differences among entries for stem breakage with pendi methalin rates at 0.56, 1.68, and 2.80 kg ha(-1). Significant differen ces 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 pend imethalin were 0.7* and 0.8**, respectively. Although the field and g reenhouse evaluations were not in complete agreement, the relative per formance of the entries provided evidence that greenhouse screening is an effective tool to characterize genetic variation in soybean for re sistance to brittle bean syndrome.