Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2006
Publication Date: 12/1/2006
Citation: Engle, J.S., Madden, L.V., Lipps, P.E. 2006. Distribution and pathogenic characterization of pyrenophora tritici-repentis and stagonospora nodorum in ohio. Phytopathology 1355-1362. Interpretive Summary: Wheat leaves from across the major wheat growing regions of Ohio were sampled to determine which fungal pathogens were the most common. Two pathogens, Stagonospora nodorum and Pyrenophora tritici-repentis were the most prevalent pathogens obtained. It was determined through statistical analysis that there was not an association of these two pathogens on wheat plants across the state. S. nodorum and P. tritici-repentis cause similar symptoms on wheat leaves, but cause different effects to yield loss. To determine the impact of each pathogen on yield loss across the state, experiments were conducted to learn more about the pathogens. One of these experiments was examining the aggressiveness of S. nodorum isolates from different regions of the state. The results of this experiment showed that the NE corner of the state has isolates that were less aggressive then the rest of the state. This could be explained by the fact that this region of the state is separated from the other regions by urban areas and has lower wheat production then the rest of the state. Another region of the state had more aggressive isolates then the rest of the state. This region has high wheat production and uses reduced tillage practices when planting wheat. These reduced tillage practices help the fungus to survive during the winter months and become established in the wheat crop earlier in the season. The experiment on P. tritici-repentis determined which races of the fungus were present in the different regions of the state. By knowing which races were present, researchers can breed the correct resistance into the wheat cultivars that farmers may plant.
Technical Abstract: To determine the distribution of Stagonospora nodorum and Pyrenophora tritici-repentis on wheat in Ohio, flag leaves with lesions were collected from wheat producing counties in 2002 and 2003. Counties were arbitrarily grouped into seven regions. Log-linear analysis of pathogen presence within regions indicated that the presence of S. nodorum was independent of the presence of P. tritici-repentis. A logistic analysis revealed that the occurrence of both pathogens varied by regions in one or both years. The aggressiveness of S. nodorum isolates was determined by inoculating two susceptible genotypes with a sub-sample of isolates from each region from both years. S. nodorum isolates obtained from an isolated region with few wheat fields were less aggressive than those from other regions. Isolates obtained from one region surrounded by regions with high wheat production annually were significantly more aggressive than those obtained in the remaining five regions. Isolates from the five other regions did not differ significantly (P > 0.05) in aggressiveness. Races 1, 2, and a few race 3 isolates of P. tritici-repentis were detected in Ohio. The distribution of P. tritici-repentis races 1 and 2 were not associated with any region, although the prevalence of race 1 was three times greater than race 2. The rarer race 3 was associated with three dispersed regions.