VIEW ARTICLE

Ecology and Epidemiology

Distribution of Pythium aphanidermatum in Rhizosphere Soil and Factors Affecting Expression of the Absolute Inoculum Potential. M. E. Stanghellini, Department of Plant Pathology, University of Arizona, Tucson 85721; L. J. Stowell(2), W. C. Kronland(3), and P. von Bretzel(4). (2)(3)(4)Department of Plant Pathology, University of Arizona, Tucson 85721. Phytopathology 73:1463-1466. Accepted for publication 25 May 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1463.

The surface area of a mature sugar beet tap root commonly exceeds 500 cm². With a direct isolation method, an average of 32% of the 1 cm² soil samples from the root-soil interface (RSI) of 10 rhizosphere sections of soil from sugar beet tap roots contained P. aphanidermatum. A bioassay with potato tuber tissue also showed that an average of 36% of the surface area of the RSI from 19 rhizosphere sections of soil contained an infective population of P. aphanidermatum. Inoculum densities within infested areas ranged from one to five oospores per 0.1 cm³ of RSI soil. The distribution of inoculum densities within the RSI of individual rhizosphere sections ranged from clustered, to random, to uniform. Inoculum densities effective for infection, as bioassayed with potato tuber tissue, were located primarily within 1 mm of the host surface. Maximum infection occurred at soil temperatures of 27 C or greater under wet soil conditions (0 to - 0.1 bar) and time periods of 24- 48 hr.