potato late blight fact sheet washington state university

Sporangia can travel as far as 15-20 km. Spread over longer distances, across countries and continents, occurs in tubers used as 'seed' for planting. Spread of late blight over short to moderate distances between plants and fields occurs as sporangia and zoospores in wind or wind-driven rain. Under those conditions, sporangia and zoospores spread the disease rapidly and fields of potato are destroyed in a less than 2 weeks. Oospores germinate and produce sporangia.Įpidemics of late blight occur when night temperatures are cool, followed by warm days with mists and rains. There are two ways of doing this depending on temperature: (i) in warmer conditions (21-26☌), the spores germinate like seeds and infect the plant directly, or (ii) in cooler conditions (18-22☌) each spore produces 6-8 smaller spores (called 'zoospores') which burst out of the larger spore and swim short distances over the plant surface before germinating and infecting. Sporangia and zoospores survive only for a few days in plant remains or in the soil.īy contrast, oospores are resting spores they have thick walls for survival either in plant remains, in the soil or in the tubers. If the sporangia land on a potato plant, and the surface is wet, they germinate.

The sporangia on the leaves, stems and tubers within the cottony growth are spread by wind, rain and water splash. Late blight has two ways of reproducing (i) spores called 'sporangia' are produced without going through a sexual process or (ii) spores called 'oospores' are produced when two strains (A1 and A2) come together and mate. Plants are destroyed a few days after the first spots appear. Rots can also form later in apparently healthy tubers in storage. Spores, formed in the white cottony growth at the edge of the spots on leaves (Photo 2) and stems, wash into the soil and infect the tubers through cracks, 'eyes' (buds) and lenticels, and cause brownish-reddish rots (Photo 3) the tubers become soft and smelly as bacteria invade and destroy them. Within a few days the leaves turn yellow, shrivel and die (Photo 1). The spots are not limited by the leaf veins. Brown irregular-shaped spots occur on the leaves spreading from the tips and margins and expanding rapidly. Symptoms on potato and tomato are similar. The life cycle, however, has many fungal-like characteristics. Phytophthora infestans is not a fungus, but an oomycete or a water mould, related to algae. There is evidence of strains attacking either potato or tomato, and there may be species that are specific to other hosts. 261), and wild species in the potato ( Solanum) family, e.g., nightshade ( Solanum nigrum). It is recorded on 'Solanaceae' from American Samoa. It is recorded on potato from American Samoa, Australia, Fiji, New Caledonia, New Zealand, Papua New Guinea. Asia, North, South and Central America, the Caribbean, Europe, Oceania. Life cycle of late blight, Phytophthora infestans.

Potato late blight fact sheet washington state university