The effect of 2,4-dichlorophenoxyacetic acid on the formononetin content of Dwalganup subterranean clover

Abstract

Two pot culture experiments were done, the first in an open-sided glasshouse and the second in a controlled environment cabinet. The sodium salt of 2,4-dichlorophenoxyacetic acid (2,4-D) was applied as a spray, at sublethal levels, to young clover plants. Increasing levels of 2,4-D led to a progressive decrease in the formononetin concentration (percentage of dry matter) in the clover leaves. At the highest 2,4-D levels of 112 48 mg/m2 (1 12 mg/m2 = 1 lb/acre), formononetin concentrations fell to one-half to one-third of the untreated control values. In the first experiment plant dry weights and leaf numbers were decreased by almost 50 % at high 2,4-D levels. In the second experiment-of much briefer duration-the rate of leaf production was also strongly decreased. Practical implications of the results are discussed briefly, and it is suggested that 2,4-D influences isoflavone synthesis by some means other than via carbohydrate metabolism.