The population genetics ofSeptoria tritici(teleomorphMycosphaerella graminicola)

The DNA-based markers of molecular genetics were combined with the analytical tools of population genetics to learn about the population biology of the wheat pathogen Mycosphaerella graminicola. DNA-based genetic markers, including restriction fragment length polymorphisms in nuclear and mitochondrial DNA, DNA fingerprints, and electrophoretic karyotypes were used in combination to show that the amount and distribution of genetic variation within and among field populations of M. graminicola is similar around the world. Measures of gametic disequilibrium suggested that the sexual stage of reproduction has a more significant impact on the genetic structure of M. graminicola populations than asexual reproduction. A field experiment conducted over a 3-year period showed that populations had a high degree of genetic stability over time. The potential effects of selection were quantified in a cultivar mixture experiment with four wheat cultivars that varied in resistance to M. graminicola. In combination, these experiments demonstrated the utility of selectively neutral genetic markers to elucidate the population genetics of fungi. Key words: genetic diversity, wheat, gene flow, RFLPs, DNA fingerprinting.