A MODEL SYSTEM FOR THE STUDY OF 2,4-D TRANSLOCATION IN LEAFY SPURGE

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Abstract
A model system was devised to study the translocation of 2,4-D in leafy spurge (Euphorbia esula L.). The effects of rate of 2,4-D application, decapitation, and rate and pretreatment with ethephon on 14C-2,4-D translocation were studied. Rooted cuttings were obtained by rooting newly-developed axillary shoots in moist vermiculite for 4 wk. These cuttings were then placed in liquid nutrient medium for translocation experiments. Seven days after application, 50–60% of the 14C translocated from 14C-2,4-D treated leaves was found in the stem. The percentage of 14C that accumulated in the stem increased with increasing rate of 2,4-D application to 1 kg/ha. Up to 85% of 14C translocated to the root was released into the nutrient medium. Shoot decapitation 5 mm below the apex up to 4 days before 2,4-D application decreased 14C percentage in leaf tissue and increased 14C in stem and root. Foliar application of ethephon at 1 kg/ha resulted in a transient increase in the rate of ethylene evolution from shoot and root tissues, decreased the amount of 14C translocated to the root zone and increased the 14C in the leaves. Ethephon treatment of larger, vermiculite-grown plants also decreased 14C accumulation in the roots. These results indicate that the use of root cuttings is a convenient and reliable method for the study of herbicide translocation and plant growth regulator/herbicide interactions in leafy spurge.Key words: Translocation, 2,4-D, leafy spurge, Euphorbia esula L., plant growth regulator, ethephon