Regarding fungicide resistance, which statement is true?

• A. It is more likely with multi-site action
• B. It is more likely with single-site action
• C. It never happens
• D. It only occurs in bacteria

Answer: (B)

When fungicide resistance happens, it comes down to how many targets need to be changed in the fungus. A fungicide that hits a single molecular site creates a very specific target. A single genetic change at that site can stop the fungicide from binding or working, so that mutant lineage is selected for and spreads. Because only one alteration is needed, resistance can arise quickly under selection pressure.

If a fungicide affects multiple sites or pathways, the fungus would generally have to acquire several independent mutations to overcome all those effects. That’s far less likely, so resistance develops much more slowly and less often. Real-world examples show single-site fungicides can lose effectiveness faster due to a single-point change, while multi-site products tend to be more durable—though not immune to resistance with intense or prolonged use.

So the statement that resistance is more likely with single-site action is the best answer.