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Soil Moisture, Root System Density, and Infection of Roots of Pinto Beans by Fusarium solani f. sp. phaseoli Under Dryland Conditions. Paul Dryden, Graduate student, Department of Biology, Utah State University, Logan 84322; Neal K. Van Alfen, professor, Department of Biology, Utah State University, Logan 84322. Phytopathology 74:132-135. Accepted for publication 24 August 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-132.

Fusarium solani f. sp. phaseoli is a chronic pathogen of dryland pinto beans (Phaseolus vulgaris) in the southwestern United States. Root system density in the soil was studied in relation to pathogen propagule density, root infection, and soil water availability. Root system density varied with the time elapsed after planting and depth in the soil, with the majority of the roots being located between 15 and 45 cm deep. Pathogen-propagule density corresponded to that of the root system, except that few propagules were found below 60 cm. Root infection occurred primarily above 45 cm. Soil water availability was greatest below 60 cm during the month when the beans were maturing. The spatial relationship in the soil between root system density, infection by the pathogen, and soil water availability indicates that infection of roots occupying the soil volume between the surface and 45 cm deep should have little deleterious effect on a plant' s water relations because of the lack of available water above 45 cm. Approximately 50% of the roots were in this region of the soil.