Plant Pathology - Horticulture (vegetables)
Vegetable - Potato
Disease Name - Late Blight
Causal Organism - Phytophthora infestans
History
Beginning of late blight of potato recorded from Andes mountain of South America.
It believed that disease introduce to Europe from South America in early 1840s.
From Europe to other countries.
Caused Irish Famine in Ireland in 1845-46.
In India disease reported from Nilgiri Hills between 1870 and 1880.
Symptom
Disease infect almost all parts of plant like leaves, stem and tubers.
Initially water-soaked lesion develop on tip and margin of leaves .
Water-soaked lesion increase rapidly.
Lesion turned brown to purplish black, necrotic under favourable weather.
Light brown to dark brown lesion appear at stem and petioles.
Which may girdle the affected plant.
Stem become weak and collapse and causing death above the lesion.
Tubers may infected by rain-washed sporangia.
Tubers show small to large irregular slightly depressed area of brown to purplish skin.
Mycelium extent to internal tissue of tubers.
Infected tubers invaded by bacteria and other secondary pathogen cause soft rot in field or poor ventilated storage.
Etiology
Anamorphic stage
Mycelium - Coenocytic, hyaline, branched, inter cellular having simple to club shape haustoria.
Sporangiophores - Slender, hyaline, sympodially branched, indeterminate, septate.
Sporangia - form on tip of sporangiphores, hyaline, thick walled. Lemon shaped, papillate.
Zoospore - emerge by sporangia at low temperature, biflagellate one tinsel while other are whiplash type.
Germ tube - emerge directly from sporangia at high temperature.
Telomorphic stage
Heterothallic - Requires two mating type A1 and A2 for sexual reproduction.
In india A1 common and A2 prevalence in shimmla hills.
Antheridia - Amphygynous male sexual organ .
Oogonia - Spherical female sexual organ.
Oospore - Thick walled form after fertilization and depends on A1 and A2 combination and tuber genome
Disease Cycle