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Genetic Structure of Setosphaeria turcica Populations in Tropical and Temperate Climates

April 1998 , Volume 88 , Number  4
Pages  322 - 329

Dorothea S. Borchardt , H. Günter Welz , and Hartwig H. Geiger

University of Hohenheim (350), Institute of Plant Breeding, Seed Science and Population Genetics, D-70593 Stuttgart, Germany

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Accepted for publication 15 December 1997.

Northern leaf blight, caused by Setosphaeria turcica, is a serious disease of maize in temperate and tropical environments. To examine the pathogen's population structure, we analyzed 264 isolates from four different continents with 70 random amplified polymorphic DNA markers and determined their mating types. Tropical populations (from Kenya, Mexico, and southern China) had an extremely high genotypic diversity, no or only weak gametic phase disequilibrium, and an even distribution of the two mating types, indicating frequent sexual recombination. Temperate populations (from Europe and northern China) had a much lower genotypic diversity, strong gametic phase disequilibrium, and an uneven distribution of mating types, indicating that sexual recombination has been rare. Populations in different continents were genetically isolated. They shared no haplotypes and carried several “private” alleles. The number of migrants between continents and between regions (between northern and southern China, western and central Kenya, and Europe west and east of the Alps) was estimated to be less than one per generation. Multivariate statistics suggested a greater relatedness of populations from the same continents than from different continents. Within agroecological zones, migration must be extensive. The potential within populations of S. turcica for adaptation should be regarded as very high, especially in tropical climates.

© 1998 The American Phytopathological Society