VIEW ARTICLE

Disease Detection and Losses

Comparisons of Spatial Patterns of Oospores of Peronosclerospora sorghi in the Soil and of Sorghum Plants with Systemic Downy Mildew. W. Schuh, Former graduate student, Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, College Station 77843, Present address: Department of Plant Pathology, Oklahoma State University, Stillwater 74078; M. J. Jeger, and R. A. Frederiksen. Associate professor, Professor, respectively, Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, College Station 77843. Phytopathology 78:432-434. Accepted for publication 12 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-432.

The spatial pattern of sorghum systemically infected with downy mildew and of soil-residing oospores of Peronosclerospora sorghi was assessed using Morisita’s index of dispersion. A binary series of quadrat sizes, starting at 1 m² and ending at 128 m² for infected plants and at 512 m² for the oospores, respectively, formed the basis for the computation. The pattern was clumped (P = 0.01) for oospores and infected plants at all quadrat sizes except the 32-m² and 64-m² quadrat size for the oospore pattern. The behavior of the index was similar for both populations. The use of susceptible plants to assess spatial patterns of oospores of P. sorghi instead of direct sampling by soil cores is indicated.