VIEW ARTICLE

Distribution of Fusarium solani f. sp. phaseoli and Bean Roots in Relation to Tillage and Soil Compaction. D. W. Burke, Research Plant Pathologist, Plant Science Research Division, ARS, USDA, Irrigated Agricultural Research and Extension Center, Prosser, Washington 99350; L. D. Holmes(2), and A. W. Barker(3). (2)(3)Agricultural Research Technicians, Plant Science Research Division, ARS, USDA, Irrigated Agricultural Research and Extension Center, Prosser, Washington 99350. Phytopathology 62:550-554. Accepted for publication 20 December 1971. DOI: 10.1094/Phyto-62-550.

Propagules of Fusarium solani f. sp. phaseoli were found distributed throughout the plowed layer (20-30 cm depth) of sandy loam and silt loam bean fields in Central Washington. Numbers in each field varied with season and location from about 100 to 5,500/g dry soil. In contrast, the pathogen was seldom detected in platings of subsoil (33-41 cm depth), but it was isolated from sparse root lesions on plants grown 2-4 weeks in pots of subsoil. Root excavations revealed that many bean roots also were confined to the plowed soil layer. Root obstruction was caused by compact soil within and below the plowed layer, but especially at the plow sole and at a disk sole formed during herbicide incorporation. Roots penetrating or evading areas of compact soil reached depths of 100 cm or more. Fewer roots entered the subsoil in Fusarium-infested fields than in noninfested fields. However, in a Fusarium-infested field containing undecomposed barley crop residues, the soil was less dense, and bean root penetration was more extensive than in adjacent fields containing only bean crop residues.