Sporangia in oomycetes are formed in the absence of light if relative humidity is high and temperature are high enough. In the morning during and after such periods you will find potato sprouts covered by white sporangia. Plants formed by latent or symptomatically infected tubers show extended systemic growth in periods with water logging. Systemic growth is enforced by high relative humidity and by high soil water content or low soil oxygen content. infestans grows like other oomycetes in the intercellular area of its hosts. The quantities with which we have to expect latent infected seeds is depending on the blight epidemics of the last season in the seed producing area. This showed that we have to expect this in the potato seed. Newer laboratory methods enabled us to check for latent infected tubers in the potato seed. Still of greater importance is the hibernation in infected tubers left as volunteers on the field because of undersize or other reasons or damped on the field as waste form potato storage. This is reported for Europe since the last 25 years. Oospores will only be formed in places where two different mating types of P. In the cool climate during winter the pathogen will find no green tissue and it has to hibernate in infected tubers or in its fruiting bodies the oospores. The economic important plants under its hosts are potato, tomato and egg plant. It can only live in the green tissue of its hosts. It is one of the most important diseases and therefore numerous models are available for it. It has led to starvings and emigration when it came to Europe. Potato Late Blight caused by Phytophtora infestans is one of the most devastating plant diseases.
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