Diclofop and MCPA Influence on Coleoptile Growth

Abstract

Experiments were conducted using theAvenacoleoptile straight-growth test to determine the influence of diclofop {2-[4-(2,4-diclorophenoxy)phenoxy] propanoic acid}, as the acid or methyl ester, and MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} on coleoptile growth of several species. Diclofop ester was a three-fold stronger inhibitor of oat (Avena sativaL. ‘Terra’) coleoptile growth than the free acid. The concentration of diclofop ester needed to inhibit 50% of the oat coleoptile growth was not influenced by IAA (indole-3-acetic acid) concentration. Oat coleoptile growth in the presence of 5 μM IAA plus 5 μM diclofop ester increased for 2 h after treatment and then decreased, so that the coleoptile length was less at the end of the 24-h assay period than at the beginning of the diclofop-ester treatment. Diclofop ester inhibited the coleoptile growth of wild oat (Avena fatuaL.) > oat > wheat (Triticum aestivumL. ‘Era’) > corn (Zea maysL. inbred ‘A-239’) > corn inbred ‘CI-66’. MCPA added to the treatment solution did not overcome oat coleoptile growth inhibition from diclofop ester or acid.