Late blight of potato | Phytophthora infestans | Irish potato famine | disease cycle

Late blight of potato | Phytophthora infestans | Irish potato famine | disease cycle | Symptom

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Late blight of potato | Phytophthora infestans | Irish potato famine | disease cycle | Symptom
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causal organism
Irish famine
Symptoms and sign
Explanation of late blight of potato
Potato
Late blight is caused by the fungal-like oomycete pathogen Phytophthora infestans. The primary host is potato, but P. infestans also can infect other solanaceous plants, including tomatoes, petunias and hairy nightshade. These infected species can act as source of inoculum to potato.
Irish Famine
The Great Famine, also known as the Great Hunger, the Famine or the Irish Potato Famine, was a period of mass starvation and disease in Ireland from 1845 to 1849, which constituted a major and historical social crisis which had a major impact on Irish society and history as a whole.
Start date: 1845
Total deaths: 1 million
Location: Ireland
Consequences: Permanent change in the country's demographic, political, and cultural landscape
Impact on demographics: Population fell by 20-25% due to death and emigration
DISEASE CYCLE
P. 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. The pathogen needs living plant or tuber tissue to survive in the field in the absence of oospores.
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. 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.
Infected potato tubers are the primary source of inoculum for P. infestans. 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. infestans on other host plants. 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.
The late blight pathogen is favored by free moisture and cool to moderate temperatures. Night temperatures of 50 to 60 F and day temperatures of 60 to 70 F are most favorable for disease development. Free water from rain, dew and overhead irrigation sprinkler irrigation all provide the water necessary for pathogen infection and development.
Spores develop in three to five days and require 12 hours of free moisture for infection to occur. Lesions on leaves and stems become visible as small flecks within a few days after infection.
The lesions expand to water-soaked, gray-green areas on the leaf and sporulate if conditions are favorable. The spores are carried by wind and rain to healthy plants, where the disease cycle begins again. A disease cycle can occur every five to seven days, resulting in rapid spread and movement of late blight.
Tubers are infected by spores washed from lesions to the soil. Spores germinate and swim to tubers in free water and infect primarily the eyes. Tuber infections are characterized by patches of brown to purple discoloration on the potato skin. Cutting just below the skin reveals a dark, reddish-brown, dry, corky rot.
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