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Botrytis fabae Sardina
Botryotinia fuckeliana (de Bary) Wetzel

Mycologia, FUNGI IMPERFECTI, HYPHOMYCETALES, MONILIACEAE .

Crops attacked: horse bean, .

[R]Common Names :

Chocolate spot disease

Occurs in all the areas where broad beans are grown. Its incidence seems higher in the Mediterranean countries.

Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images

[R]Identification
The fungus can be cultured on growth medium.
The conidia are detectable with a light microscope and are larger than the B. cinerea conidia.

[R]Description
At the beginning of the life cycle a large number of spots appear, called "chocolate spots" several mm in diameter, circular on the leaflets, petals and pods and elongated on the stems.
The spots increase and coalesce turning into rust-coloured necrotic lesions of irregular form on all the plant organs.
The leaves drop off early and the plants lodge.

[R]Biology
The fungus overwinters as sclerotia which sporulate and produce conidia in spring in wet conditions. The conidia contaminate all the plant organs and cause the "chocolate spots".

[R]Epidemiology
The fungus thrives in an optimum temperature of 15 -20 °C.
High RH (>80%) is necessary for conidial sporulation on the spots.
Conidia are wind-dispersed. The presence of free water on the leaves is not necessary for conidial contamination to take place, high RH (>90%) is sufficient.
In dry weather the fungus remains dormant in the host tissues or grows slowly.
In humid conditions there is rapid inter- and extracellular spreading of the disease.

[R]Treatement
The selection of tolerant cultivars is in progress.

[R]Possible misleading
Ascochyta fabae when the B. fabae spots show concentric rings due to alternating humid and dry conditions but the B. fabae has no pycnidia.
With the lesions of Botrytis cinerea which frequently occur at the extremity of the leaves or on the already blighted edges.

[R] Images

  1. Botrytis fabae , Chocolate spot disease (TIVOLI B., INRA)
    Horse-bean chocolate spot disease Chocolate spots on horse-bean leaves (aggressive symptoms).
  2. Botrytis fabae , Chocolate spot disease (TIVOLI B., INRA)
    Horse-bean chocolate spot disease Chocolate spots on horse-bean leaves.
  3. Botrytis fabae , Chocolate spot disease (LAMARQUE C., INRA)
    Horse-bean chocolate spot disease Necrosis of the agressive phase of Botrytis fabae .
  4. Botrytis fabae , Chocolate spot disease (BASF)
    Horse-bean chocolate spot disease Reddishing of a horse-bean stem infected by the chocolate spot disease.
  5. Botrytis fabae , Chocolate spot disease (TIVOLI B., INRA)
    Horse-bean chocolate spot disease Sclerotia of Botrytis fabae on horse-bean stems.
  6. Botrytis fabae , Chocolate spot disease (TIVOLI B., INRA)
    Horse-bean chocolate spot disease Beginning of the epidemics of chocolate spot disease on horse-bean plant : the parasite attacks leaves and flowers.
  7. Botrytis fabae , Chocolate spot disease (TIVOLI B., INRA)
    Horse-bean chocolate spot disease Chocolate spots on leaves(aggressive symptoms).

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