Glyphosate resistance is more variable than paraquat resistance in a multiple-resistant hairy fleabane (Conyza bonariensis) population.

摘要

Reduced control of some glyphosate-resistant hairy fleabane populations with paraquat has raised concerns about evolved multiple resistance to both glyphosate and paraquat. The objective of this study was to confirm the presence of multiple-resistant (glyphosate and paraquat) hairy fleabane populations in California. A series of dose-response experiments was conducted to evaluate the effect of glyphosate and paraquat in a known susceptible (S) and putative multiple-resistant (R) population of hairy fleabane. The greenhouse experiments were conducted during summer, fall, and winter under controlled temperature and natural light conditions. Multiple-resistant hairy fleabane was identified; however, the level of resistance to glyphosate varied substantially among seasons. During the summer, the glyphosate rate required to reduce growth by 50% (GR₅₀) for the R population was 0.94 kg ae ha-1, 5.2-fold more than for the S population. In the fall and winter experiments, however, the R population response to glyphosate was similar to the S population with a GR₅₀ of 0.22 kg ae ha-1 or less. Multiple-resistant plants were controlled in the fall and winter at rates that did not control the same population during summer. GR₅₀ of paraquat varied among seasons (0.94, 0.24, and 0.07 kg ai ha-1 during summer, fall, and winter, respectively); however, plant mortality was more consistent. This is the first reported case of glyphosate-paraquat resistance in hairy fleabane and the multiple-resistant population could pose a significant challenge to annual no-till and perennial cropping systems in California. Further research on the mechanisms of resistance and the physiological factors underlying the seasonally variable response to glyphosate is needed.