What is cross resistance in plants with respect to herbicides?

• A. A plant is resistant to only one herbicide
• B. A plant is resistant to two or more herbicides with the same mode or site of action
• C. A plant has developed immunity to all herbicides
• D. A plant shows enhanced growth when treated with herbicides

Answer: (B)

Cross resistance in plants refers to the phenomenon where a plant that has developed resistance to one herbicide also exhibits resistance to one or more additional herbicides that share the same mode or site of action. This means that the plant has adapted in such a way that the biochemical or physiological mechanisms it uses to resist one herbicide can also counteract the effects of other herbicides that operate similarly.

This is significant in agricultural practices as it can complicate weed management and herbicide effectiveness. Understanding cross resistance is crucial for developing effective weed control strategies and selecting herbicides or management practices that can reduce the selection pressure for resistance in weeds.

In contrast, resistance to only one herbicide, immunity to all herbicides, or enhanced growth in response to herbicide treatment are not indicative of cross resistance and do not reflect the relationships of resistance among herbicides with similar modes of action.