Phytophthora infestans acquires reversible resistance

Phytophthora infestans can activate resistance to the fungicide mefenoxam (metalaxyl-M) after a single exposure to low concentrations of the product. The discovery, made by researchers at the Boyce Thompson Institute and the Universidad de los Andes, reveals a dynamic and worrying behavior of the pathogen that causes the disease. late blight.

The research showed that strains originally sensitive to the fungicide began to grow even in media containing high doses of the product after prior contact with low doses. Resistance, however, did not lead to increased sporulation. The pathogen survived, but did not multiply more than before.

The observed behavior does not follow the classic pattern of fixed genetic mutations. According to the authors, the phenomenon resembles an epigenetic mechanism. Resistance is temporary. Just one exposure to fungicide-free media is enough for the pathogen to lose its ability to resist. Re-exposure to a low concentration of the product reactivates the mechanism.

Resistance process

The process is linked to pleiotropic drug resistance (PDR), a strategy in which cellular pumps eliminate the fungicide from the body. Activating this system consumes energy, which may explain why the pathogen abandons resistance when the risk disappears.

In addition to reversible resistance, the researchers observed that repeated exposure to high concentrations of mefenoxam neither strengthened nor weakened the activated defense. The pathogen maintained its ability to survive, without further changes.

Further information at doi.org/10.1094/PDIS-05-25-1110-RE