Studies on Some Sudanese Members of the Genus Cercospora.

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El Rahman, El Nur El Amin Abd
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Twenty morphological characters of thirty Cercospora species collected in the Sudan were used for a quantitative numerical classification. This revealed 83% overall similarity between C. arisaemae on Abutilon sp. and C. gossypiana on Gossypium hirsutum, and 75% overall similarity between C. cucurbitae on Cucumis sativus and C. sesami on S. orientale and between C. gomphrenae on G. globosa and C. coffeicola on C. robusta. This high level of morphological similarity suggests that these species may be conspecific and cross inoculation tests are suggested for each pair for confirmation. The other 24 species showed less than 65% overall similarity, which suggests them to be fairly distinct and cross – inoculation tests are therefore not necessary. Four Cercospora species, C. calotropidis, C. rhynochosiarum, C. sesame and C. nicotianae were isolated on artificial cultural media and investigated for cultural and pathological characters. This is the first record of the isolation of C. calotropidis and C. rhynochosiarum in artificial culture media. Cultural investigations of the four species are reported. Cross inoculation tests showed that each species was specialised for its host of occurrence, but could also infect a few of the related host plants tested. The susceptibility of 85 local and introduced varieties of sesame to the economically important C. sesame was investigated. Some of the sesame varieties were immune to infection, while others showed different levels of susceptibility. The local varieties on the whole showed more resistance to the disease than the introduced varieties.
morphological characters, Cercospora, . calotropidis, C. rhynochosiarum, C. sesame