PATHOLOGICAL STUDIES ON DAHLIA TUBER ROTS

Abstract

Dahlia (Dahlia pinnata L.) is one of the most popular and attractive cut flower plants around the world. Many fungi like Sclerotium rolftii, Fusarium so/ani and Macrophomina phaseoli and bacteria like Erwinia carotovora pv. carotovora, E. carotovora pv. chrysanthemi, Pseudomonas cichorii and Bacillus polymyxa are attacking dahlia plants in the field, storage and during propagatioby stem or divided cuttings. The obtained results of the present study could be summarized as follows: I. Sum of 107 fungal and 55 bacterial isolates were obtained from naturally infected dahlia tubers in three locations i.e. Moshtohor, El-Dair and El-Manashy m Kalubia Governorate. The isolated fungi belong to 6 genera and 7 species. Fungi were identified as: S. rolftii, Fusarium sp., R. so/ani, A. niger, A. jlavus, P. digitatum and Rhizopus sp. S. rolftii was more occurrence in all tested samples. The highest isolation number and frequency % of S. rolftii was recorded in El-Dair location followed by Moshtohor and El­ Manashy locations respectively. 2. S. rolftii was the most pathogenic fungus in inducing rotting of dahlia tubers followed by R. so/ani and Fusarium sp. 3. As for physical factors affecting growth of S. rolftii, The fungus was able to grow on most of the tested media. PDA was the best followed by dahlia tuber agar and Brown's media, while the lowest average of linear growth occurred on Haren's and Czapek's media.