Biological control of downy mildew on onion plants [electronic resource].

Includes references.

Downy mildew is a potentially serious disease of onions (Allium cepa L.) particularly when onions grown under cool, moist, and humid conditions. The disease is caused by the air-borne fungus Peronospora destructor (Berk.) Casp. which is a common destructive disease of onion in Egypt. Numerous of microbial isolates (50) were isolated from healthy onion leaf surfaces. These isolated microorganisms comprised bacteria (70%), fungi (25%), actinomycetes and yeasts (5%). The initial screening of these isolates which were carried out under greenhouse conditions resulted the selection of 4 different bacterial isolates and one fungal isolate exhibited potency against P. destructor. The microscopic examination of downy mildew on treated leaves using light microscopy revealed dead and lysis of sporangia (conidiospores) and sporangiophores of the tested fungal pathogen. The predominant effective bacterial isolates belonged to Bacilli and Pseudomonads. They were identified as Bacillus subti/is and Pseudomonas sp. and the fungal isolate was identified as Trichoderma harzianum. Bioassays were conducted under greenhouse conditions at the experimental greenhouse, Fac. of Agric., Kafr EI-Sheikh Univ., Egypt. Open field experiments using two onion cultivars,

Summary in Arabic.

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