Growth‐Promoting Activity of Chlordimeform

Early season applications of the insecticide chlordimeform [ N ' ‐ (4‐chloro‐o‐tolyl)‐ N , N ‐dimethylformamidine] (CDF), have increased cotton ( Gossypium hirsutum L.) lint yields above those expected from the pesticidal properties of the chemical. The molecular structure of CDF resembles other agricultural chemicals that have cytokinin‐like activity. The objective of this research was to determine whether CDF possesses biological activity similar to these compounds. Chlordimeform was compared with the naturally occurring cytokinin zeatin in two hormone bioassays (radish [ Raphanus sativa L.] cotyledon expansion and cytokinin‐depleted soybean [ Glycine max L.] callus growth). Chlordimeform induced radish cotyledon expansion when the cotyledons were incubated under continuous light. The optimal CDF concentration for cotyledon growth was 5.1 ✕ 10 −4 M . Although expansion occurred under light conditions, CDF inhibited chlorophyll synthesis at the higher concentrations and did not induce growth when cotyledons were incubated in the dark. These responses were contrary to the response of cotyledons incubated with zeatin. Also, no activity was found in soybean callus culture. The data suggested that CDF has plant physiological activity, but the biological activity is not identical to that of zeatin.