http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Studies on Septoria tritici blotch of wheat in Texas
xiii, 84 leaves : illustrations, map ; 28 cm
Septoria tritici blight (STB) epidemics caused by the fungus Septoria tritici Rob. ex Desm. have become prominent in recent years over the coastal, eastern and north central regions of Texas where the weather is generally favorable for the development of the disease. The purpose of this work was to explore several facets of STB epidemiology and biology in Texas. Efforts to determine the presence of the sexual stage of the pathogen were successful. Pseudothecia and asci containing ascospores, that conformed to the description of Mycosphaerella graminicola, were found from September 1989 until March 1990 on leaves and sheaths of naturally infected wheat plants. Plants inoculated with ascospores developed symptoms characteristic of STB and produced typical S. tritici pycnidia. The infection process of ascospores were longer, and required a higher level of humidity than infection by conidia. Electrophoresis of total DNA showed four low molecular weight bands in S. nodorum isolates which were missing in all S. tritici isolates. The bands consisted of ssRNA as indicated by acridine orange staining. Restriction patterns of the S. nodorum isolates were unmistakably distinct from those of S. tritici. At least one dimorphism was detected among S. tritici isolates. Pathogenic variation was detected among S. tritici isolates as expressed on the disease progress curves on each of 22 wheat cultivars. An aggressiveness pattern was detected for each isolate, but exceptions indicated an isolate-cultivar interaction. Disease levels of natural infections on several locations and years could not be predicted, and varied depending an a specific year-location combination. Disease levels evaluated at one time were correlated with disease progress curves generated by 4-5 evaluation times.