The timing of exogenous 2,4-dichlorophenoxyacetate (2,4-D) application affects nodulation of soybeans, glycine max (L.) merr

Abstract

The effects of exogenous addition of 2.26 μM 2,4-dichlorophenoxyacetate (2,4-D) at the time of sowing and 3 d after on nodulation and nodule function were investigated in soybean [Glycine max (L.) Merr.] cvs. “Enrei,” “Lee,” and “Nanbushirome.” Both treatments especially that at the time of sowing considerably depressed shoot and root development. The total number of cortical cell division foci/cm lateral root was similarly increased 2-8 fold by the treatments but the increase in the number of nodules/cm lateral root in plants treated 3 d after sowing was generally twice that of the treatment at the time of sowing. Majority of the cortical cell divisions, notably in treated plants, was arrested at the nodule developmental stage before nodule emergence. The total number of nodules at harvest (24 d after sowing) relative to the control was increased in plants treated 3 d after sowing but was decreased by the earlier treatment. Nevertheless, treated plants showed a similar nitrogenase (acetylene reduction) activity on a plant basis, and the specific nodule activity was highly variable indicating that nodule activity is independent of both nodule number and weight. The possible role of 2,4-D in nodulation is discussed. © 1991 Taylor & Francis Group, LLC.