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Soil Water Matric Potential Requirements for Root-Hair and Cortical Infection of Chinese Cabbage by Plasmodiophora brassicae. R. Dobson, Research assistant, Western Washington Research and Extension Center, Puyallup 98371; R. L. Gabrielson(2), and A. S. Baker(3). (2)(3)Plant pathologist and soil scientist, Western Washington Research and Extension Center, Puyallup 98371. Phytopathology 72:1598-1600. Accepted for publication 7 July 1982. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-1598.

This research was undertaken to define the soil moisture necessary for infection of Chinese cabbage by Plasmodiophora brassicae. Matric potentials required for infection were determined by using both tension plates and a semipermeable membrane/polyethylene glycol system. Both root-hair and cortical infections decreased with decreasing availability of water. Water potential necessary for cortical infection was measured in three soil types: no infection was observed at < 150 mbars in silt and sandy loam soils, but was found at 200 mbars in a muck soil. In a silt loam soil, cortical infection required more moisture (> 150 mbars) than root-hair infection (< 200 mbars). The requirement for more soil moisture (and thus, larger water-filled soil pores) is consistent with the postulated need for fused and, therefore, larger secondary zoospores necessary to initiate cortical infection.