Reduced sensitivity to fluazinam detected in the rapidly increasing Phytophthora infestans clonal lineage EU-37 (Dark Green 37)

EuroBlight annually monitors and reports upon the development of Phytophthora genotypes in Europe. The results of 2016, which in many countries was a serious late blight year, showed that two relatively new genotypes are on the rise. Their survival and spread at a time when other clones have failed to establish suggests they are evolutionarily fit and may pose challenges to disease control. One of these genotypes is EU-37.

Spreading

A single sample of EU-37 was first detected in the Netherlands in 2013 and was sampled locally at a low frequency in the following two seasons. However, it comprised 5.5% of the EU-population sampled in 2016, having spread as widely as England, Germany, Belgium, the Netherlands and NW France.

So far it was assumed that EU-37 could establish due to its fitness. Current results indicate that other characteristics also contribute to the increase of this genotype.

Results from Wageningen University & Research shows that all P. infestans EU-37 isolates tested, displayed a reduced sensitivity to fluazinam. The isolates tested originate from the Netherlands and Germany. They were obtained from fields with a clear reduced efficacy of fluazinam or from potato stores with unexpectedly high tuber blight infection levels. Further research has to establish whether all EU-37 isolates display excellent fitness and reduced sensitivity to fluazinam.

Strategy to reduce risks

To avoid reduced efficacy of fluazinam in commercial potato production, it is important to follow resistance management recommendations: reduce the selection pressure exerted by fluazinam by limiting the number of applications with fluazinam-containing products and alternate with other active ingredients. Also the use of products in which fluazinam is combined with other active ingredients lowers the selection pressure. Implementing the resistance management recommendations could possibly, besides preventing problems with a disappointing efficacy, also prevent the further rise of EU-37 (Dark Green 37).