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Guignardia baccae (Cavara) Jacz.
Guignardia bidwellii (Ell.) Viala et Ravaz

Mycologia, ASCOMYCOTINA, DOTHIDEALES .

Crops attacked: grapevine .


[R]Common Names :

False black-rot of grapevine,

Occurs in Europe and Japan ; in Portugal described since 1894.

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


[R]Identification
Under naked eye, the pycnidia are visible as small black spots, in the beige stains of the stems, or as ascostroma (false perithecia).
The fungus can be grown in artificial nutritive media.

[R]Description
Elongated unilateral stains in early ripened shoots which, later on, become beige, near the base of the shoots and nearer internodes.
Irregular necrosis of the tissues, spreading to the branches.
Longitudinal fissures caused by the swelling of the tissues in the basal area, due to strangling of the shoot.
Later, by July, basal disarticulation as a result of the weight of the bunches and of the wind.
Necroses in the petioles and leaf veins.
Brown stains, roundish and depressed, on the berries,at maturation.
Wilt of the bunches, caused by reddish or brownish necrosis in the peduncle and main branching of the rachis.

[R]Biology
The fungus overwinters, as perithecia and pycnidia and also as dormant mycelium in the buds and base of shoots.
The infection starts from the ascospores and pycnidiospores germination, through the base of the shoots or nearer internodes, penetrating in the internal tissues of the xylem.
Pycnidia, small and numerous are formed in the vine shoots.

[R]Epidemiology
The ascospores and pycnidiospores are carried by the wind and rain drops.
The rain plays an important role in the melting of the cirrhus that are formed in the pycnidia (the birds and insects are also dispersing agents).
The infection occurs after the bud bursting as a result of the spore germination (ascospores or pycnidiospores) that fall on the young shoots (phenologic stages D and E) and in the zones not ripened or affected by cold wheather in autumn.

[R]Treatement
Prophylatic and chemical preventive measures similar to those used for Phomopsis viticola .

[R]Possible misleading
Phomopsis viticola but this one forms, in the vine shoots, silver coloured stains with black spots (pycnidia) big and scattered, whereas in the M. flaccida the stains are beige with small and numerous spots.

[R] Images

  1. Guignardia bidwelli , Grapevine black rot (BUGARET Y., INRA)
    Grapevine black rot View through the light microscope of a grape showing a cut through the fructifications (perithecia) on its surface.
  2. Guignardia bidwelli , Grapevine black rot (CARTOLARO P., INRA)
    Grapevine black rot Light microscope view of a cut through a perithecium on the surface of a grape.
  3. Guignardia bidwelli , Grapevine black rot (CARTOLARO P., INRA)
    Grapevine black rot Black-rot damage on a leaf petiole showing the pycnidia (black dots) in the process of liberating pycnidiospores in the form of cirrhi.
  4. Guignardia baccae , Grapevine black rot (TOMAZ I., MA)
    Grapevine black rot Elongated beige lesions at the base of grapevine shoots as a result of black-rot.
  5. Guignardia bidwelli , Grapevine black rot (BUGARET Y., INRA)
    Grapevine black rot Bunch of grapes attacked by Guignardia bidwelli .
  6. Guignardia bidwelli , Grapevine black rot (BUGARET Y., INRA)
    Grapevine black rot Mumified grape, covered with pycnidia, that was attacked by Guignardia bidwelli .
  7. Guignardia bidwelli , Grapevine black rot (CARTOLARO P., INRA)
    Grapevine black rot Grape that has been mummified by Guignardia bidwelli .
  8. Guignardia bidwelli , Grapevine black rot (BOSSENNEC J-M., INRA)
    Grapevine black rot Small, light brown, patches due to Guignardia bidwelli on the leaves of a grapevine shoot.
  9. Guignardia bidwelli , Grapevine black rot (BOSSENNEC J-M., INRA)
    Grapevine black rot Fine detail of the small, light brown, necrotic patches due to Guignardia bidwelli on the leaves of a grapevine shoot.

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