The effects of diclofop‐methyl on root growth of wild oat

Abstract

Diclofop‐methyl severely reduced the growth of seminal roots of wild oat (Avena fatua L.) when applied in hydroponics at 0.01 and 0.05 μM. Lateral roots emerged closer to the seminal root apex than in the controls, but coronal root number and length were unaffected at 0.01 μM. However, doses of 0.05 to 0.1 μM induced more but shorter coronal roots to emerge than for controls. At 1 μM the number and length of coronal roots were less than for controls. Root‐applied diclofop‐methyl at 1 μM inhibited emerging second leaf growth to the same extent as a foliar dip in 1 μM diclofop‐methyl without causing chlorosis as foliar treatment does. Because of limited basipetal transport of foliarly‐applied diclofop‐methyl, shoot treatment was ineffective in inducing abnormal root morphogenesis of the seminal and lateral root systems, although it caused abnormalities of the coronal root system. Time course studies were initiated to examine the effect of root‐applied diclofop‐methyl at 0.05 μM. Seminal root growth was inhibited (by diclofop‐methyl) soon after treatment, while controls continued elongating. The distance between the seminal root apex and the first lateral primordia increased in the controls within one day after treatment, but decreased in the herbicide‐treated roots. The distance between the seminal root apex and the first emerged lateral root was reduced by three days after treatment. The number of lateral primordia and emerged roots was unaffected three days after treatment. These dose‐response and kinetic results suggested that diclofop‐methyl caused a loss of apical dominance in the seminal root.