Seasonal development
and life cycle—Seed piece decay
Seed piece decay is usually caused by the combined action of the Fusarium fungi that cause dry
rot in potatoes and the Erwinia bacteria that cause blackleg, although decay can sometimes be caused
by Fusarium alone. Fusarium spores are present virtually everywhere in the soil. They germinate
and infect the freshly cut surfaces of seed pieces, causing lesions that later may be invaded by Erwinia.
When seed pieces are infected by both Erwinia and Fusarium, losses from seed piece decay
are much greater than when Fusarium is present by itself. Cool soil that is too wet or too dry
favors the development of seed piece decay.
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Dry
rot in potatoes caused by Fusarium spp.
 Erwinia
in potato tuber causing blackleg
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