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Lettuce Anthracnose

Lettuce Anthracnose caused by Microdochium panattonianumis is an important disease of lettuce worldwide. The first symptoms of anthracnose appear as small circular to angular water soaked lesions on the lower leaves. Centres of lesions become necrotic and often fall out leading to a shot hole appearance. Similar sunken lesions on the veins develop and form pits along the midribs. In severe outbreak, anthracnose lesions coalesce and leaf tissues turn brown and may result in entire crop loss. The pathogen is able to survive in infested debris.

Microsclerotia have been reported as source of inoculum and can survive in the soil as long as 4 years. Rain, free water, splashing water and cool wet weather are important in dispersal of fungal propagules and conidia on the lower leaves to initiate the disease. Because the pathogen is favored by leaf wetness, cool conditions, and high humidity.

Anthracnose: Conditions for Infection: Free water from rain, dew, or sprinkler irrigation is required for spore dispersal, germination, and infection by this pathogen. The fungus infects plants through stomata or penetrates the leaves directly.

  • The optimum temperature for infection is at 20° to 22°C.
  • Infection can occur over a range of 5° to 30°C.
  • Spores can germinate and infect in as little as 2-4 hours if there is continuous leaf wetness.
  • Microsclerotia require 4-6 hours under optimum conditions for germination and infection.
  • Spores are produced in lesions on leaves and are spread to other leaves primarily by splashing water.
     

The FieldClimate.com Antracnose Infection Model is initiated by rain and uses the temperature leaf wetness duration rule graphed out beside.

In FieldClimate.com we determine two infection ways:

a) Conidia Infection 
b) Infection by microsclerotien 

End of June both conidia and microsclerotien had favourable conditions to infect plant tissue.

Literature:

Microdochium panattonianum B. Sutton, Galea & Price APPS Pathogen of the month February 2009
ANTHRACNOSE ON LETTUCE, Plant Diseases Washington state University extension service