Pathogenic characterization, distribution in Ohio and wheat genotype reactions to Stagonospora nodorum and Pyrenophora tritici-repentis

Two fungal pathogens, Stagonospora nodorum and Pyrenophora tritici-repentis infect wheat leaves, the spike and impact seed quality. Both fungi produce host specific phytotoxins that elicit distinct lesion types. The distribution and pathogenic characterization of these pathogens was determined in seven wheat growing regions of Ohio. Both pathogens were recovered from wheat flag leaves from all seven regions, but S. nodorum was most prevalent. There was an association between S. nodorum isolate aggressiveness and region of the state. Isolates from North Eastern Ohio were less aggressive than those from the remaining 6 regions, while isolates from Central North West Ohio were more aggressive. P. tritici-repentis exists in the U.S. as a population of races, with the most common being races 1--4. These races are characterized by the toxin(s) produced causing specific reactions on a differential set of wheat cultivars and lines. Isolates of P. tritici-repentis in Ohio were determined to be races 1, 2 and rarely race 3, representing 60%, 35% and 5% of the population, respectively. Seedling reactions of 15 wheat cultivars and one breeding line to races 1 and 2 of P. tritici-repentis indicated that some cultivars were more susceptible to race 2 than race 1. This same set of cultivars was inoculated with isolates of S. nodorum producing either predominately phytotoxins SnTox1 or SnTox2. Most genotypes were more sensitive to S. nodorum isolate producing predominately SnTox2. Spike and flag leaf reactions to S. nodorum of 13 wheat cultivars were examined in the greenhouse and field. Cultivar Coker 9663 was identified as having moderately high resistance to both leaf blotch and glume blotch. Seed harvested from field plots were examined for pathogen infestation. S. nodorum was the predominant pathogen on seed obtained from both inoculated and noninoculated field plots. P. tritici-repentis and Bipolaris sorikiniana were also present on seed from non-inoculated plots. This same set of cultivars was examined for P. tritici-repentis resistance in the greenhouse and field. The resistance levels to P. tritici-repentis of the 13 cultivars varied in the field with no significant differences detected among Cultivar reactions. Two greenhouse experiments examined the response of wheat cultivars to P. tritici-repentis on adult flag leaves. (Abstract shortened by UMI.)...