Reversibility of the action of 2,4-dichlorobenzoic acid, a synthetic herbicide, on cucumber seedlings by strains of soil microorganisms

The herbicide, 2,4-dichlorobenzoic acid (DCLBA), was administered through t he nutrient solution to six cucumber seedlings grown hydroponically. DCLBA, which is also a synthetic auxin, stunts cucumber plants at a low concentra tion but kills at a higher one. Roots of six comparable seedlings, treated with DCLBA, were exposed to two strains of microorganisms, TS-22 and TS-29, and Rhizoplane AC1, which were isolated from soils and cucumber roots. The control cucumber seedlings, unexposed to DCLBA and the different strain s of microorganisms grew vigorously, whereas those exposed to DCLBA were st unted. The stature of seedlings, exposed simultaneously to DCLBA and TS-22, TS-29, and Rhizoplane AC1, was nearly that of the control, but their fresh and dry weights were approximately 2/3 and 1/2, respectively, of the untre ated control seedlings. These results demonstrate that there are microorganisms in the soil and on cucumber roots which, if added to the nutrient solution, can catabolize DCL BA.