New Phytophthora populations: A shift from indirect to direct sporangial germination?

Phytophthora infestans, the causal agent of potato- and tomato late blight, remains a serious threat for (commercial) potato and tomato production. In North Western Europe, frequent fungicide applications, mostly aimed to prevent infection, form the back bone of potato late blight control. Modern protectants such as Shirlan (a.i. fluazinam) are highly effective against (germinating) P. infestans sporangia and zoospores. Zoospores in particular are so sensitive to low concentrations that the many applications over the past two decades may well have exerted sufficient selection to pressure against the formation of zoospores. Thus, over the years the balance between direct and indirect germination may have shifted towards direct germination. This hypothesis was investigated at Bayer Crop Science and Plant Research International