When the leaves are infected, water-soaked green-brown spots appear at the tip or edge of the leaves, and there are light green halo around the spots. When the humidity is high, the spots expand rapidly and become brown, and a circle of white mold, namely sporangiophore and sporangium, is produced, especially on the back of the leaves; When drying, the diseased spots turn brown and dry, brittle and easy to crack, and there is no white mold, and the expansion speed slows down. The stem or petiole is stained with brown stripes. The seriously diseased leaves drooped and curled, and eventually the whole plant was black and rotten, and the whole field was scorched and gave off a rotten smell. The tubers are infected with brown or purple-brown patches, which are slightly sunken, and the potato flesh under the skin of the affected area is also brown, slowly expanding or rotting around.
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