Studies on the mechanism of resistance to the herbicide quinciorac in smooth crabgrass Digitaria ischaemum

摘要

Quinciorac failed to control a significant proportion of the smooth crabgrass [Digitaria ischaemum (Schreb. ex Schweig) Schreb. ex Muhl] infestation at a turf site in Tulare County, California, when this herbicide was first used on that site in the mid-eighties. Dose response studies with plants treated in post-emergence confirmed the strong resistance of this biotype to quinciorac. The susceptible (S) biotype responded to quinciorac treatment with increased ethylene production, while this increase was minimal in the resistant (R) biotype. Parallel to the increase in ethylene production, there was a buildup of cyanide in tissues of the S biotype; cyanide is a co-product of ethylene biosynthesis. Pre-treatment of plants with the ACC synthase inhibitor AVG prior to quinciorac application resulted in less ethylene and cyanide production and higher smooth crabgrass growth than when plants were treated with quinciorac only. These data suggest a target site-based mechanism of resistance involving the accumulation of cyanide derived from stimulated ACC synthesis (a precursor of ethylene). In addition, the basal beta-cyanoalanine synthase activity in shoots of the R biotype was about four times higher than in the S biotype, suggesting a higher ability todetoxify cyanide.