Seasonal development
and life cycle—Powdery scab
The fungus that causes powdery scab survives in the soil as resting spores, which form the spore balls
released from tuber and root lesions. Stimulated by the presence of susceptible host roots, resting spores
germinate to produce mobile spores that swim through soil water to infect roots or stolons. These infections
produce additional spores that spread infection to roots and tubers.
Resting spores survive in the soil for up to 6 years and can survive passage through the digestive tract
of animals. The fungus can also infect and produce resting spores on the roots of other potato family
plants such as tomato and nightshades. Powdery scab is favored by cool, moist conditions, and symptoms
are most severe on white- and red-skinned tubers.
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