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Enhanced Colonization of Pea Taproots by a Fluorescent Pseudomonad Biocontrol Agent by Water Infiltration into Soil. C. M. Liddell, Research associate, Department of Plant Pathology, 1630 Linden Drive, University of Wisconsin, Madison 53706, Present address: Department of Entomology, Plant Pathology and Weed Science, New Mexico State University, Las Cruces 88003; J. L. Parke, assistant professor, Department of Plant Pathology, 1630 Linden Drive, University of Wisconsin, Madison 53706. Phytopathology 79:1327-1332. Accepted for publication 12 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1327.

Root colonization by an introduced strain of Pseudomonas fluorescens was examined to determine the importance of the root apex in passive transport and to quantify the effect of infiltrating water on distribution of the bacterium. Pea seeds coated with strain PRA25rif of P. fluorescens were sown in columns containing a sandy field soil at soil-water matric potentials of 1, 6, or 10 kPa. After 7 days, the largest population density of the bacterium was found on roots at 1 kPa, but the bacterium was detected on only 5% of root segments 45 cm below the seed, approximately 8 cm above the root apex. At 6 and 10 kPa, the bacterium could not be detected on roots beyond 3 cm from the seed, more than 16 cm from the root apex. Addition of 27.2 and 54.4 mm of water to the top of the columns 4 days after planting increased the depth from which PRA25rif was recovered. The bacterium was detected on root segments at least 910 cm from the seed 24 hr after water was applied. Transport of the bacterium on the root apex apparently was limited to a short period after seed germination, but the bacterium was carried long distances by percolating water.

Additional keywords: biological control, Pisum sativum, rhizosphere.