VIEW ARTICLE

Disease Detection and Losses

Analysis of Spatial Patterns in Sorghum Downy Mildew with Morisita's Index of Dispersion. W. Schuh, Graduate research assistant, Department of Plant Pathology & Microbiology, Texas Agricultural Experiment Station, College Station 77843; R. A. Frederiksen(2), and M. J. Jeger(3). (2)(3)Professor, and associate professor, respectively, Department of Plant Pathology & Microbiology, Texas Agricultural Experiment Station, College Station 77843. Phytopathology 76:446-450. Accepted for publication 29 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-446.

The distribution and spatial pattern of sorghum plants systemically infected with Peronosclerospora sorghi were determined by using Morisita's index of dispersion. A contiguous area of 1,300 m² was assessed for disease incidence twice during the growing season at two locations. Each assessment was done by using eight quadrat sizes (binary series from 1 m² to 128 m²). The spatial pattern of diseased plants was clumped at each date and location as determined by the use of Morisita's index. Several clump sizes, which were in a hierarchical order, were detected at each location. Comparison of clump sizes between assessment dates showed a reduction in average clump size which was attributed to premature plant death. The distribution of the data could not be fitted to known probability distributions with statistical significance.