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Evidence for Natural Selection in the Mitochondrial Genome of Mycosphaerella graminicola

March 2004 , Volume 94 , Number  3
Pages  261 - 267

J. Zhan , G. H. J. Kema , and B. A. McDonald

First and third authors: Institute of Plant Sciences, Phytopathology Group, ETH Zentrum/LFW, Universitätstrasse 2, CH-8092 Zürich, Switzerland; and second author: Plant Research International, B.V. P.O. Box 16, 6700 AA Wageningen, The Netherlands

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Accepted for publication 9 December 2003.

Pathogenicity assays were combined with restriction fragment length polymorphism (RFLP) markers in the mitochondrial and nuclear genomes to compare Mycosphaerella graminicola populations adapted to bread wheat (Triticum aestivum) and durum wheat (T. turgidum) in the Mediterranean Basin. The majority of isolates had unique nuclear DNA fingerprints and multilocus haplotypes. Only six mitochondrial DNA (mtDNA) haplotypes were identified among 108 isolates assayed. There were minor differences in frequencies of alleles at nuclear RFLP loci between the two host-adapted populations, but differences in the frequencies of mtDNA haplotypes were highly significant (P < 0.0001). mtDNA haplotype 1 dominated on the isolates adapted to bread wheat, and its frequency was twice as high as for the isolates adapted to durum wheat. mtDNA haplotype 4, which contained a unique ≈3-kb insertion, was detected only in isolates showing specificity toward durum wheat and was the dominant haplotype on this species. We propose that the low mitochondrial diversity in this pathogenic fungus is due to a selective sweep and that differences in the frequencies of mtDNA haplotypes between the two host-adapted populations were due to natural selection according to host species.

© 2004 The American Phytopathological Society