|Camargo, L E|
Submitted to: Genetics and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2008
Publication Date: 11/19/2008
Citation: Brunelli, K.R., Dunkle, L.D., Sobrinho, C.A., Fazza, A.C., Camargo, L.E.A. 2008. Molecular Variability in the Grey Leaf Spot Pathogens in Brazil. Genetics and Molecular Biology. 31:939-942. Interpretive Summary: Gray leaf spot (GLS) of corn is one of the most economically important diseases of corn in the world. Disease severity reached epidemic levels during the mid-1990s in the U.S.A., the late 1990s in Africa, and the early 2000s in South America. Our previous work had shown that the fungal pathogen causing GLS in the U.S. is comprised of two genetically distinct but morphologically and taxonomically identical sibling species and that the pathogen population in Africa consisted of only one of those siblings. The results of molecular and morphological analyses of the GLS pathogen in Brazil indicated that the population was comprised of the same two sibling species as those in the U.S. and that both pathotypes were distributed throughout the corn-growing regions of the country. Both pathotypes in the U.S., Brazil, and Africa were found to be genetically very similar, indicating that sources of GLS resistance in corn germplasm would likely be effective in each of the three continents. This information will be useful to corn breeders and geneticists in screening and selecting for GLS resistance and to plant pathologists in determining the genetic variability in pathogen populations and in studies on evolution of pathogenic fungi.
Technical Abstract: Isolates of Cercospora species from leaves displaying typical symptoms of gray leaf spot were collected in maize-producing areas of south-central Brazil in 2001 and 2002. Restriction digests of the internal transcribed spacer region of rDNA detected the presence of the same two Cercospora species described on maize in the United States. These species, previously designated C. zeae-maydis group I and group II, correspond to C. zeae-maydis and the recently described species, C. zeina, respectively. Genetic variability among isolates was assessed by analyzing 104 amplified fragment length polymorphism loci. Cluster analysis confirmed the genetic separation of isolates into two distinct groups with a mean similarity of 35%. Similarity levels within each species were high, averaging 93% and 92% among isolates of C. zeae-maydis and C. zeina, respectively. The mean genetic similarity between C. zeae-maydis and C. zeina and two isolates of C. sorghi f. sp. maydis was 45% and 35%, respectively. Differences in conidium length, although small, were significant between the two species. Results of this study showed that populations of the gray leaf spot pathogens in Brazil are similar to those in the United States and that C. zeina, the predominant pathogen in Africa, is also present in Brazil.