One hundred and fifteen fungal isolates representing nine fungal species were isolated from six rose cultivars grown in both outdoor and greenhouses at Giza and Qalubiya governorates during April, 2009. The occurrence of each fungus varied from cultivar to another. Isolation trials showed that Coniothyrium fuckelii and Alternaria alternata were the most dominant ones, followed by Nigrospora sp. Meanwhile, Cercospora sp. showed the lowest frequency.
Pathogenicity test showed that C. fuckelii was the only pathogenic fungus and was able to cause the rose stem canker. Symptoms are usually begun as small yellow to red spots on the bark and gradually expand. The centres of the cankers become light brown and the margin a darker brown. Cankers may girdle the stem causing wilting and death of the plant parts above the canker. Small pycnidia are sometimes produced on the canker.
The causal fungus was identified as C. fuckelii Sacc., the anamorph of Leptosphaeria coniothyrium (Fuckel) Sacc., according to its morphological features and pathogenic potentially. As the authors are far aware, rose stem canker and C. fuckelii, the causal fungus are described herein for the first time in A.R. Egypt.
Reaction of five rose cultivars was tested against four isolates of C. fuckelii. All the tested isolates were pathogenic to cvs. African Dawn, First Red, Mercedes, Sentrix and Vercellia Rose. No correlation was found between virulence of isolates and their origin. Cv. Vercellia Rose was the highly susceptible, while Sentrix was the least susceptible one.
The reaction of nine plant species belonging to different families to the four tested isolates revealed that C. fuckelii isolates failed to infect any plant species tested, except for Syngonium podophyllum which showed slight infection with isolate No. 1 and isolate No. 4 isolated from cvs. African Dawn and Vercellia Rose, respectively.
Differentiation among the four tested isolates of C. fuckelii was assessed by the use of Random Amplified Polymorphism DNA technique (RAPD), which showed high similarity levels (85.56%) with primer OPC5 as compared to (76.73%) with primer OPG 14. The two primers showed obvious variation in isolate No. 1 isolated from cv. African Dawn, where the results of genetic analysis showed two DNA bands with primer OPC5 and three bands with primer OPG14 compared to eight bands in rest isolates.