Differential Varietal Response of Root Tissues to Exogenous Growth Regulators in Soybeans, Oats and Corn 1

1 3 3 1 6 2 7 2 7 5 8 2 1 5 9 2 2 2 6 1 9 8 3 1 HE use of plant growth regulators in weed and crop T control has become an accepted agricultural practice. The apparent selectivity of growth regulating substances, in general, and 2,4-dichlorophenoxyacetic acid in particular, exhibited between species of plants has resulted in wide usage of such substances as herbicides. A number of investigators have indicated that crop varieties or strains also may differ in response to exogenous growth regulators (1 , 2, 3, 4, 5 , 7, 8, 9, 12, 13)." However, in many of these experiments only a few varieties have been tested so that only a limited amount of the available genetic material has been sampled. Other studies, often involving the same varieties, have shown conflicting results. In this study, a large number of varieties of soybeans and oats and inbred lines of corn were screened by a laboratory root suppression test to determine differences in response to exogenous growth regulators. By use of this root inhibition test a wide range of germ plasm could be examined and classified as to relative tolerance to specific growth compounds. This technique has certain limitations as it ignores the importance of morphological characteristics of above ground plant parts in determining differential response to chemicals. 2,4-dichlorophenoxyacetic acid, 2,4,54richlorophenoxyacetic acid, isopropyl N-phenylcarbamate and naphthalene acetic acid4 were selected to test differential varietal response.