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Title:   Author  item
                                            ADHIKARI, TIKA - NORTH DAKOTA STATE UNIV.item
                                            ALI, SHAUKAT - NORTH DAKOTA STATE UNIV.item
                                            BURLAKOTI, RISHI RAM - NORTH DAKOTA STATE UNIV.item
                                            SINGH, PAWAN KUMAR - NORTH DAKOTA STATE UNIV.item
                                            MERGOUM, MOHAMED - NORTH DAKOTA STATE UNIV.item
                                            Goodwin, Stephen

                                                         - *Steve*
  Submitted to: Journal of Phytopathology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 8/13/2007
                                    Publication  Date: 12/14/2007
                                    Citation: Adhikari, T.B., Ali, S., Burlakoti, R., Singh, P., Mergoum, M., Goodwin, S.B. 2007. Genetic structure of Phaeosphaeria nodorum populations in the north-central and mid-western United States. Journal of Phytopathology. 98:101-107.Interpretive Summary: Stagonospora nodorum blotch (SNB), caused by the fungus Phaeosphaeria nodorum, is a very destructive foliar disease of wheat worldwide. However, relatively little is known about the population biology of this fungus in the major wheat-growing regions of the central United States. To rectify this situation, 308 single-spore isolates of P. nodorum from 12 populations in Indiana, Minnesota, North Dakota, and Ohio, were analyzed for genetic variation with five molecular markers and for mating type. Most populations had high levels of genetic diversity, and the level of genetic diversity was higher in the spring wheat population in North Dakota and Minnesota than in the winter wheat population from Indiana and Ohio. Migration of individuals was high between populations within each region but low between geographically distant populations. Most of the total genetic variation occurred within populations, but about 25% was due to genetic differences between the hard red spring and soft red winter wheat production regions. The two mating types occurred in approximately equal frequencies in each population tested, and analyses of molecular markers indicated that sexual reproduction probably occurs regularly in populations of P. nodorum in the major wheat-growing regions of the central United States. Isolates from the North Dakota population showed some differences in their abilities to infect spring wheat cultivars with different levels of resistance. This information will be useful to population geneticists to understand the patterns of reproduction and migration occurring within and among populations of this fungus, to plant pathologists trying to devise better methods of disease control, and to plant breeders to develop new cultivars with durable resistance to SNB.
                                Technical Abstract: Stagonospora nodorum blotch (SNB) caused by Phaeosphaeria nodorum is a very destructive foliar disease of wheat worldwide. However, relatively little is known about the population biology of this fungus in the major wheat-growing regions of the central United States. To rectify this situation, 308 single-spore isolates of P. nodorum from 12 populations in Indiana, Minnesota, North Dakota, and Ohio were analyzed for genetic variation at five microsatellite loci and the mating type locus. Most populations had high levels of gene (HS = 0.152 to 0.530) and genotype (D = 0.600 to 0.972) diversity. Gene diversity was higher in the spring wheat population (HS = 0.503) from North Dakota and Minnesota than in the winter wheat population (HS = 0.269) from Indiana and Ohio. Populations sampled from the same wheat production area had high genetic identities and low genetic distances. Gene flow was high between populations within each region but low between geographically distant populations. Overall, 62% of the total genetic variation was distributed within populations, while 25% was due to differentiation between the hard red spring and soft red winter wheat production regions. Analyses of mating type frequencies and multilocus disequilibrium tests indicate that sexual recombination probably occurs regularly in the populations analyzed. Evaluation of isolates from the North Dakota population on spring wheat cultivars with different levels of resistance to P. nodorum revealed some differential effects. These data suggest that sexual reproduction occurs regularly in P. nodorum populations in the major wheat-growing regions of the central United States. This information can help breeding programs develop new cultivars with durable resistance to SNB.


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