SOME EFFECTS OF 2,4‐D, DDT, AND COLORADO 9 ON THE BACTERIA RHIZOBIUM LEGUMINOSARUM FRANK IN THE ROOT NODULES OF THE COMMON BEAN

Abstract

IN A PREVIOUS study (Payne and Fults, 1947) ,some of the effects of 2,4-D (2,4-dichlorophenoxy acetic acid), DDT (1-trichloro-2,2-bis-(p-chlorophenyl) ethane) and Colorado 9 (1-trichloro-2,2bis-(p-bromophenyl) ethane) on the number of bacteria root nodules of the common bean were reported. The compound 2,4-D in relatively minute amounts (2 to 16 p.p.m. of soil) and DDT in somewhat higher concentrations (127 p.p.m.) decreased nodulation. The insecticide Colorado 9 (List and Payne, 1947) at the same concentrationis had no effect in decreasing the number of nodules. In tests where these chemicals were sprayed on rapidly growing plants, there was little change in nodule numbers. However, when sectioned many were found to be soft and slimy although the plants from which they came appeared normal otherwise. This suggested that there might be significant morphological and physiological changes in the bacteria. The objective of this study was to determine the effect of 2,4-D, DDT and Colorado 9 on the nodule bacteria i?hizobium leguminosarum Frank of cornmon beans.3 The criteria used for determining these effects were changes in the Gram stain reaction, bacteria rod lengths, and nodule smear populations. MATERIALS AND METHODS.-The kind of beans used throughout the study was the pencil-pod golden wax variety. All planits were grown in 6inch clay pots, five to the pot, in a sanldy loam soil in the greenhouse of the Colorado Agricultural Experiment Station between January 16 and March 5, 1946. Nodules were collected from the roots of common beanis that had the following treatments: plants grown in soil treated with DDT and Colorado 9