#WHITE BLIGHT DEFINITION FREE#
Spores germinate and swim to tubers in free water and infect primarily the eyes.
Tubers are infected by spores washed from lesions to the soil. A disease cycle can occur every five to seven days, resulting in rapid spread and movement of late blight. The spores are carried by wind and rain to healthy plants, where the disease cycle begins again. The lesions expand to water-soaked, gray-green areas on the leaf and sporulate if conditions are favorable. Lesions on leaves and stems become visible as small flecks within a few days after infection. Spores develop in three to five days and require 12 hours of free moisture for infection to occur. Free water from rain, dew and overhead irrigation sprinkler irrigation all provide the water necessary for pathogen infection and development. Night temperatures of 50 to 60 F and day temperatures of 60 to 70 F are most favorable for disease development. The late blight pathogen is favored by free moisture and cool to moderate temperatures. The pathogen can be transmitted from infected seed tubers to newly emerging potato plants, where it produces airborne spores that can move to neighboring plants. That includes potatoes in storage, infected tubers missed during harvest that remain unfrozen during the winter (volunteers), seed tubers and infected cull piles, and P. Infected potato tubers are the primary source of inoculum for P. Although soil survival is not known to occur definitively in the U.S., anecdotal evidence indicates that sexual combination has occurred, suggesting soil survival is possible.
However, in some areas of the world where both mating types of the pathogen are present, a sexual spore that is capable of soil survival is produced. The pathogen needs living plant or tuber tissue to survive in the field in the absence of oospores. infestans, the cause of late blight, is a heterothallic fungal-like pathogen, meaning two mating types are required for sexual reproduction and are referred to as A1 and A2.
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