TECHNICAL DOCUMENT ON DOWNY MILDEW OF SOYBEANS | Asian Journal of Plant and Soil Sciences

Downy mildew is a prevalent disease in field-grown soybean [Glycine max (L.) Merill], but it is rarely found in greenhouses. Soybean downy mildew is a widespread disease caused by the fungus-like organism Peronospora manshurica (Class Oomycetes; Phylum Oomycota), which can persist in crop leftovers and on seed surfaces. P. manshurica possesses zoospores (flagellate motile spores) and can only be infected with water or high humidity. Wind and rain carry spores onto plants, and illness spreads swiftly in a field during periods of chilly, wet, or high humidity. Saclike sporangia carried on sporangiophores emerge from the stomata of the lower surface of the leaves in P. manshurica. There will be pale green to light yellow dots on the upper surface of the leaves. The patches become pale yellow and uneven in size and shape as they grow larger, and they may turn into lesions. In wet weather, the mildew fungus produces a pale blue to grey downy growth on the lower surface of the leaves, immediately opposite the lesions on the top side. Although the disease rarely causes major damage to soybeans, it has been reported that when it is present early in the season and in high levels, it reduces seed size and quality. The goal of this technical document is to look at the symptoms and signs of soybean downy mildew, as well as the cause, epidemiology, illness development, disease cycle, ecology, and disease management.

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