Assessment of Herbicide-Induced Growth Inhibition of Soybean

Abstract

Several herbicides and growth substances were applied singly and in combination at varying concentrations to soybean [Glycine max (L.) Merr. ‘Lee’]. This was an attempt to compare the growth inhibition obtained with that previously measured in the single-celled organism Chlorella pyrenoidosa Chick, and to investigate the plant pathways and sites by which inhibition occurs. Inhibition induced by paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), and 2,4-D [(2,4-dichlorophenoxy)acetic acid] satisfactorily supported the hypothesis inherent in a kinetic analysis of such results, whereas, that induced by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and chloramben (3-amino-2,5-dichlorobenzoic acid) did not. A probit analysis of the atrazine and chloramben results indicated variability in the type of toxicity. Soybean was considerably more susceptible to 2,4-D than Chlorella pyrenoidosa but there was little difference in the type of growth inhibition response produced. Both were equally susceptible to atrazine. High concentrations of the growth regulator IAA (indoleacetic acid) were antagonistic to the growth inhibition induced by 2,4-D, while competitive inhibition occurred at the low concentration of IAA. The 2,4-D had only a slight effect on the inhibitory effect of paraquat and antagonistically interfered with that induced by atrazine.