Effect of different levels of mannitol‐induced water stress on the tolerance of cultivated oat (Avena sativaL.) to didofop‐methyl

Abstract

Summary: The effect of degree of water stress in Avena sativa on diclofop‐methyl efficacy was assessed. Within 24 h of applying stress by adding mannitol to the root medium (0 to 12.5%), the rate of leaf extension of the youngest leaves (leaves 3 and 4) decreased with increasing mannitol concentration. Without water stress, application of diclofop‐methyl had little effect on extension rate of leaves 3 and 4 during the first 4 days after spraying. Subsequently, it caused a significant decrease in the extension rate of leaf 4 with more pronounced effects on later leaves. Diclofop‐methyl had little effect on leaf extension rate of plants given mannitol. Shoot dry weight at harvest for unsprayed plants decreased with increased mannitol concentration and for sprayed plants it was greater without mannitol than with mannitol (all levels). However, at mannitol concentrations greater than 4%, shoot dry weight for sprayed and unsprayed plants was not significantly different. Sprayed plants exposed to 2–8.5% mannitol produced seed heads but those at zero mannitol did not. When the root medium of all treatments was flushed of mannitol one week after spraying, then main‐tained without mannitol, shoot dry weight at harvest for unsprayed plants decreased slightly with increased mannitol concentration applied initially. However, shoot dry weight for sprayed plants increased with increased mannitol concentration. Without mannitol two weeks after spraying, chlorophyll concentrations of leaves 3 and 4 were greater and water saturation deficit (WSD) values were lower for unsprayed plants than sprayed plants but there were no differences at 6.2% mannitol. It is proposed that tolerance to diclofop‐methyl by A. sativa as a result of water stress, is primarily due to a decreased rate of leaf expansion resulting in lower demand for membrane synthesis and less strain on membranes damaged by the herbicide.

Determination of environment‐specific dose–response relationships for clodinafop‐propargyl on Avena spp.

“…(Rioux et al ., 1974; Lemerle & Verbeek, 1995). Particular variables of importance include soil moisture stress (Boydston, 1990; Dastgheib et al ., 1990; Dickson et al ., 1990; Lemerle & Verbeek, 1995), nitrogen deficiency (Dickson et al ., 1990), temperature, light, wind, humidity and rainfall (Muzik, 1975; Doran & Andersen, 1976; Coupland, 1983, 1984; Merritt, 1984; Nalewaja & Woznica, 1985; Jensen & Kudsk, 1988; Devine, 1989; Caseley, 1990; Wicks et al ., 1993; McMullan, 1994; Madafiglio et al ., 2000). As a general principle, a lower dose of herbicide may kill most of the target weeds under favourable conditions.…”

Effect of drought stress, abscisic acid, and abscisic acid analogues on the efficacy of diclofop-methyl and tralkoxydim

“…Previous results have shown that the herbicidal activity of diclofop-methyl and structurally related herbicides can be reduced significantly under drought stress conditions (Akey and Morrison 1983, Dastgheib et al 1990, Dortenzio and Norris 1980. The results presented here confirm this point and indicate that the activity of tralkoxydim, a member of a second group of acetyl-Coenzyme A carboxylase-inhibiting herbicides, can also be reduced under moisture-stress conditions.…”

“…Drought stress has been reported to decrease the efficacy of diclofop and related herbicides (Akey and Morrison 1983, Dastgheib et al 1990, Dortenzio and Norris 1980, Wilcox et al 1987. Dortenzio and Norris (1980) reported that diclofop-methyl activity was decreased by 15-50% in wild oat grown just above the permanent wilting point, as compared with plants grown at field capacity; the maximum effectiveness of diclofop-methyi was achieved when plants were grown in high soil moisture for 2-4 days following treatment.…”

Diclofop‐methyl antagonism by broadleaf weed herbicides: the importance of leaf expansion rate

“…Previous studies indicate that diclofop-methyl phytotoxicity is primarily due to effects on meristematic tissue and young leaves must be expanding rapidly for maximum herbicide activity (Andrews et al, 1989a), The critical period during which growth rates must be high if diclofop-methyl is to be effective, appears to be approximately the first week after spraying (Andrews et al, 1989a;Dastgheib et al, 1990), The objective of the experiments described here was to determine if antagonism of diclofopmethyl by the broadleaf weed herbicides 2,4-D, bentazone, chlorsulfuron and dicamba is associated with a decrease in the rate of leaf expansion during the first few days after spraying. The rate of leaf extension was used as an indication of the rate of leaf expansion.…”