|Goodwin, Stephen - Steve|
Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/10/2011
Publication Date: 9/6/2011
Citation: Gurung, S., Goodwin, S.B., Kabbage, M., Bockus, W.W., Adhikari, T.B. 2011. Genetic differentiation at microsatellite loci among populations of Mycosphaerella Graminicola from California, Indiana, Kansas and North Dakota. Phytopathology. 101:1251-1259. Interpretive Summary: Mycosphaerella graminicola causes Septoria tritici blotch and is considered one of the most devastating pathogens of wheat. Although the genetic structures of M. graminicola populations from different countries have been analyzed using various molecular markers, relatively little is known about populations from geographically distinct areas of the United States and from spring versus winter wheat. To test the hypothesis that populations of the pathogen from different parts of the United States are genetically differentiated, 330 single-spore isolates of M. graminicola representing California, North Dakota, Indiana and Kansas were analyzed for mating type frequency and for genetic variation using molecular markers. There was high genetic diversity, a generally equal distribution of the mating types and little genetic differentiation. Almost every isolate had a unique genotype for the molecular markers analyzed as expected for sexual, but not asexual, reproduction. Interestingly, some potential deviations were noted in California, Indiana and Kansas indicating possible selection for particular gene combinations in those regions. These populations seem to have regular cycles of sexual reproduction and there is high exchange among regions and between spring and winter wheat, indicating that new resistance genes are unlikely to last long before being broken down by the fungus. This information will be useful to population geneticists and evolutionary biologists to better understand migration and recombination in M. graminicola. Plant pathologists and wheat breeders can use this information to design improved strategies for disease management and to help guide the deployment of new genes for resistance.
Technical Abstract: Mycosphaerella graminicola causes Septoria tritici blotch and is considered one of the most devastating pathogens of wheat. Although the genetic structures of M. graminicola populations from different countries have been analyzed using various molecular markers, relatively little is known about those from geographically distinct areas of the United States and from spring versus winter wheat. These are exposed to great differences in environments including temperatures, season of host-free periods, and resistance present in geographically separated wheat breeding populations so are more likely to become genetically differentiated. To test this hypothesis, 330 single-spore isolates of M. graminicola representing 11 populations from California, North Dakota, Indiana and Kansas were analyzed for mating type frequency and for genetic variation at 17 microsatellite loci. There was an equal distribution of both mating types in all locations except California. In total, 306 haplotypes were detected, almost all of which were unique. High levels of gene and genotype diversity were observed within the 11 populations. Interestingly, significant gametic disequilibrium occurred in California, one Indiana population and two of those from Kansas. High gene flow was inferred between the 11 populations, reflected by low genetic differentiation. Most of the genetic variation (> 82%) occurred among individuals within populations with a much lower proportion (< 18%) among populations. These results indicate that sexual recombination occurs frequently in the M. graminicola populations sampled, and that these geographically separated populations are genetically similar, suggesting high gene flow giving a panmictic structure even between spring and winter wheat.