VIEW ARTICLE

Ecology and Epidemiology

The Effect of Primary Inoculum Level of Pyrenophora tritici-repentis on Tan Spot Epidemic Development in Wheat. E. A. Adee, Graduate research assistant, Department of Plant Pathology, Kansas State University, Manhattan 66506; W. F. Pfender, associate professor, Department of Plant Pathology, Kansas State University, Manhattan 66506. Phytopathology 79:873-877. Accepted for publication 18 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-873.

In field experiments in two crop years, three levels of primary inoculum of Pyrenophora tritici-repentis, covering approximately a 100-fold range in residue-borne ascocarp numbers, were applied to wheat (Triticum aestivum) plots in the fall. After the appearance of initial infections in the spring, tan spot severity was rated every 5–8 days until leaf senescence, and disease progress curves were constructed. There were significant positive relationships between the area under the disease progress curves and the level of primary inoculum for both years, even though weather conditions were very different, 1987 being very wet and 1988 very dry. Statistical analysis indicated, however, that the quantitative effect of local primary inoculum on epidemic development differed between the two years; thus, the importance of local primary inoculum, relative to incoming secondary inoculum, is likely to depend on the particular conditions of the epidemic. The highest level of local primary inoculum significantly reduced yield, but confounding factors (rust infection and drought) made the overall relationship difficult to demonstrate. The experiments indicated that pathogen control measures that reduce residue-borne primary inoculum can decrease epidemic development and crop damage, despite multiple infection cycles caused by wind-disseminated secondary inoculum.