Penetration, Translocation and Metabolism of Fungicide Guazatine in Dwarf Apple Trees

Abstract

Penetration, translocation, and metabolism of a fungicide guazatine-triacetate (TA), 1, 1′-iminodi (octamethylene) diguanidine triacetate, in dwarf apple trees (Malus pumila sp., cv. ‘Inu-apple’) were determined over a period of 12 weeks under laboratory conditions by using ¹⁴C-labeled guazatine-TA. Autoradiographic studies showed that (1) no observable movement of the radiocarbon in the apple leaves occurred following foliar application of ¹⁴C-guazatine-TA to either adaxial or abaxial surface of the leaves, and (2) the rate of penetration of ¹⁴C into the apple fruits was extremely slow and a major part of ¹⁴C was retained on the surface after surface application of ¹⁴C-guazatine-TA. The results of quantitative determination for ¹⁴C in ¹⁴C-guazatine-TA treated leaves indicated the following: (1) the rate of ¹⁴C-disappearance from the leaves was exceedingly slow (T_1/2=67 weeks) with approximately 87% of the applied ¹⁴C being located in the treated leaves even after 12 weeks, and (2) the radiocarbon had poorly penetrated in the leaf tissues (21% of the applied ¹⁴C after 12 weeks). Quantitative determination of ¹⁴C in the fruits also confirmed the results of the autoradiographic observation for the fruits. The radioactive compounds dislodged from the surface of both leaves and fruits principally consisted of intact guazatine. Furthermore, several phototrans-formation products (a major product (Pm) and a few minor ones) were also detected, indicating the occurrence of photolysis of ¹⁴C-guazatine on the surfaces. The extracts from both the leaves and fruits also comprised intact guazatine as a primary radioactive component and photolysis products. Thus it appeared that guazatine and the photoproducts penetrated in the plant tissues were highly resistant to the plant metabolism. Translocation of the radiocarbon from the ¹⁴C-guazatine-TA treated leaves to symplasts (fruits and newly developed leaves after treatment) was negligible.