Practice question

Superweeds describe weedy populations that have acquired herbicide resistance via gene flow from cultivated crops, making control challenging. When transgenic crop expressing bar gene for glufosinate tolerance or cp4-epsps for glyphosate tolerance cross-pollinates with sexually compatible weed such as Brassica rapa, hybrid offspring inherit resistance allowing survival under herbicide application. Repeated selection in fields sprayed with same herbicide enriches resistant allele frequency, and backcrossing to weed parent restores weediness while retaining transgene. Documented cases include glyphosate-resistant canola volunteers and bentgrass. Resistance to insects does not provide similar advantage because herbivory rarely limits weed growth in cropped fields where competition decisive. Therefore concern about superweeds specifically links to herbicide resistance gene transfer, driving implementation of management practices like crop rotation, herbicide mode action rotation, and containment via chloroplast transformation or male sterility to reduce pollen-mediated gene escape. Population genetics model predicts rapid increase of resistance allele when selection pressure continuous, especially if herbicide applied annually over large area. Volunteer canola plants carrying transgene found outside fields illustrate escape potential. Management includes rotating herbicide modes of action, using multiple herbicide tolerant traits, and deploying crops with male sterility or chloroplast transformation. Understanding herbicide resistance transfer to weeds informs stewardship guidelines