Effects of Diclofop on Growth, Mitotic Index, and Structure of Wheat (Triticum aestivum) and Wild Oat (Avena fatua) Adventitious Roots

Abstract

Methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid} (diclofop as used herein refers to the methyl ester) added to nutrient solution inhibited adventitious root development and reduced the mitotic index in adventitious root tips of wheat (Triticum aestivum L. ‘Neepawa’) and wild oat (Avena fatua L.). Elongation of wild oat roots was significantly inhibited by 0.15 μM diclofop 24 h after treatment; whereas, wheat roots were unaffected at concentrations less than 1.5 μM even at 12 days, indicating at least a 10-fold difference in sensitivity. Initiation of new adventitious roots was reduced in both species by 0.30 μM diclofop. Mitotic index was more severely reduced at lower concentrations and after a shorter exposure in wild oat than in wheat. Histological studies showed that 24 h after wild oat roots were treated with 0.30 μM diclofop for 24 h, severe damage occurred to tissues within the developing central cylinder, close to the root apex. Disruption of cortical and epidermal cells generally was not as severe until 4 to 7 days after treatment. By 12 days the entire root tip was almost completely obliterated, with only the epidermal cell walls remaining intact.