VIEW ARTICLE

Ecology and Epidemiology

Effect of Flooding on the Soil Gas Composition and the Production of Microsclerotia by Verticillium dahliae in the Field. N. Ioannou, Department of Plant Pathology, University of California, Davis, CA 95616; R. W. Schneider(2), and R. G. Grogan(3). (2)(3)Department of Plant Pathology, University of California, Davis, CA 95616, (2)Present address: Department of Plant Pathology, University of California, Berkeley, CA 94720. Phytopathology 67:651-656. Accepted for publication 3 December 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-651.

The production of microsclerotia (MS) in tomato tissues infected with Verticillium dahliae was examined in soil subjected to different water treatments (no irrigation, one irrigation, and 10, 20, and 40 days of continuous flooding) under field conditions. About equal numbers of MS were produced in the dry and one-irrigation treatments. No, or very few, MS were produced during the flooding and this inhibition was due in large part to decreased O₂ and increased CO₂ concentrations in the flooded soil. Upon drainage, the concentrations of O₂ and CO₂ returned rapidly to normal atmospheric levels and MS production resumed. The numbers of MS eventually produced in the 10-, 20-, and 40-day flooding treatments were 90, 44, and 46%, respectively, of the average numbers in the nonflooded treatments. The reduction was significant (P = 0.05) only in the 20- and 40-day flooding treatments. Ethylene, at levels ranging from traces to about 6.5 μliters/liter was detected in all treatments. Highest concentrations occurred in flooded or nearly saturated soils with added plant debris, but there was no indication that ethylene affected the production of MS.