BLACK SPOT ON ROSE BUSHES

refineriaweb
Diplocarpon rosae
Rosa chinensis
(Lib.) F.A. Wolf
Rosal, Roser

Drepanopezizaceae, Helotiales; Leotiomycetes

Basionimo

Asteroma rosae Lib.

SYMPTOMS

D. rosae can be distinguished from other related species by its host specificity, the rose bush to which it is confined. Black spot is a very important disease of roses. It starts on the surface of the leaves as a dry reddish spot, first circular and then small spots converge to form a large irregular spot. When the disease spreads it can affect the stems where the lesions appear purple at first turning blackish. In the Mediterranean climate, the black spot appears in autumn with leaf senescence and high humidity. In summer with dry weather there are usually no problems with black spot. The fungus hibernates in dormant buds and stems and on dead leaves; conidia initiate new infections in wet weather. We have not been able to observe apothecia, which indicates that this form of reproduction is not an important source of infection.


A.B Black spots on leaves, C Conidioma rounded on leaves, radial strands of subcuticular mycelium, D Conidiogenous cell forming bicellular conidia, E Elliptical bicellular conidia constricted at the septum, F Graphic representation. of conidiogenous cell and conidia

Scale C 100 µm, D, E, F 10 µm.

DESCRIPTION

Mycelial strands composed of several filaments at first hyaline, brown when mature forming a subcuticular network. The internal mycelium connected through the epidermis to the subcuticular mycelium. Subcutaneous acervular conidioma at first covered with cuticle which is irregularly broken 150-200 µm in diameter. Polyphialidic hyaline hyaline conidiogenous cell. Conidia hyaline, oblong, elliptic with a strongly constricted transverse septum, guttulate, 20-25 x 5-6 µm.

BIBLIOGRAPHY

For more synonyms Indexfungorum.com
Brian C. Sutton, The Coelomycetes Fungi Impercti With Pycnidia Acervuli and Stromata. Commonwealth Mycological Institute p 300 (1980).
Smith I.M., Dunez J., Phillips D.H., Lelliott R.A., Archer S.A. MANUAL OF PLANT DISEASES Ediciones Mundi_Prensa (1982).

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