Cercospora zeina is the causal agent of grey leaf spot disease of maize in southern Africa
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The aim of our study was to identify the causal agent of grey leaf spot disease of maize in southern Africa. Single-conidial cultures were recovered from maize leaves with typical disease symptoms sampled from several fields in South Africa, Zambia and Zimbabwe. Morphology, cultural characteristics, and a PCR-based test using Cercospora zeae-maydis and C. zeina-specific primer sets identified all single-conidial cultures as C. zeina. In addition, sequence alignment of DNA fragments of the internal transcribed spacer region (ITS1, ITS2, and the 5.8S gene) and elongation factor 1-α grouped all cultures in the same clade as the C. zeina ex-type culture CBS 118820. To by-pass cultivation of the slow-growing fungus, a rapid method to isolate DNA directly from lesions was successfully applied for PCR identification of C. zeina with species-specific ITS and histone primers. Koch’s postulates were fulfilled for C. zeina by artificially inoculating maize plants in a greenhouse, re-isolating conidia emerging from lesions and verifying pathogen identity with molecular techniques. These results provide evidence that confirms the presence of C. zeina and absence of C. zeae-maydis in commercial maize plantations in southern Africa.
KeywordsDiagnostic species-specific PCR assay Grey leaf spot Maize Koch’s postulates Cercospora zeina Cercospora zeae-maydis
elongation factor 1-α
grey leaf spot
internal transcribed spacer
We thank Martin Coetzee for assistance with the phylogenetic analysis. The funding of this work was provided by the Department of Science and Technology through the PlantBio Trust, South Africa and a Post-doctoral Fellowship from the University of Pretoria to BM.
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