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A Test for Randomness of Infection by Soilborne Pathogens. Christopher A. Gilligan, University lecturer, Department of Applied Biology, University of Cambridge, Pembroke Street, Cambridge, CB2 3DX, U.K.; Phytopathology 73:300-303. Accepted for publication 25 June 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-300.

A simple method is described to test for randomness of infection in inoculum density experiments involving soilborne pathogens. The method tests the goodness-of-fit over a range of inoculum densities of the observed numbers of infected and uninfected roots with those predicted by the Poisson distribution. The method requires scores only of the presence-or-absence of infection on roots and not of the numbers of infections on a root. Data from inoculum density experiments involving the take-all fungus, Gaeumannomyces graminis, and seedlings of wheat and barley are used to illustrate the application of the test.