Studies on the Selective Mechanism of Pretilachlor

II. Absorption, Translocation, and Metabolism of Pretilachlor

Abstract

Involvement of pretilachlor (2-chloro-2′, 6′-diethyl-N-[2-propoxyethyl]-acetanilide) selectivity in its absorption, translocation, and metabolism was investigated in 4 gramineous species, rice (Oriza sativa L. cv. nihonbare), corn (Zea mays L. cv. honeybantam), barnyardgrass (Echinochloa oryzicola VASING.), and finger millet(Eluesine coracana GAERTN.), and two perennials Sagittaria pygmaea MIQ., and Cyperus serotinus ROTTB.. Growth retardation by pretilachlor was more severe in barnyardgrass and finger millet than in corn and rice. Sagittaria pygmaea MIQ. revealed greater tolerance than Cyperus serotinus ROTTB. Seed treatments showed higher susceptibility to pretilachlor than 3 week old seedling treatments in gramineous species but the reverse was true in perennial weeds.
Higher absorption of ¹⁴C-pretilachlor was observed in rice and barnyardgrass than in corn and finger millet, regardless of seedling ages. Both young and mature seedlings of Sagittaria pygmaea MIQ. and Cyperus serotinus ROTTB. absorbed very little ¹⁴C-pretilachlor, compared with gramineous species. ¹⁴C-pretilachlor absorbed by roots was translocated easily to shoots and distributed in all parts of the plants.
Absorbed ¹⁴C-pretilachlor changed into a water-soluble compound (s) in plants within 2 hours after treatments at 76-82% and about 60% in tolerant and susceptible sepcies, respectively. Metabolic activity was greater in the tolerant corn and rice than in the susceptible barnyardgrass and finger millet in both seedling ages, suggesting that the herbicide may be metabolized into a nontoxic water-soluble compound, the glutathione conjugate of pretilachlor, by glutathione S-transferase (GST) and that pretilaclor selectivity may be related to this activity in gramineous species. Perennial weeds also showed high activity to metabolize pretilachlor into water-soluble compound (s), even though their low GST activities.