VIEW ARTICLE

Ecology and Epidemiology

Effect of Oxygen, Carbon Dioxide, and Ethylene on Growth, Sporulation, and Production of Microsclerotia by Verticillium dahliae. 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 67:645-650. 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-67-645.

Verticillium dahliae cultured in decreasing O₂ (20.9 to 0.06%) and nearly constant CO₂ (about 0.03%) concentrations, produced maximum radial growth and sporulation at 1.9 and 2.7% O₂, respectively; growth was nil at 0.06% O₂. The production of microsclerotia (MS) was maximum at 20.9% O₂ and decreased progressively with each decrease in O₂ concentration. Under constant O₂ (17-18%) and increasing CO₂ concentrations (ranging from 0.03 to 20.9%), maximum radial growth and sporulation were produced at 6.2 and 0.03% CO₂, respectively. In 20.9% CO₂, radial growth was essentially the same as at 0.03%, but sporulation was reduced to about 20% of the maximum. The production of MS decreased with each increase in CO₂ concentration and was completely inhibited at about 12.2% CO₂. Under different mixtures of O₂ and CO₂, ranging from 20.9% O₂ and 0.03% CO₂ to 0.5% O₂ and 20.5% CO₂, radial growth was maximum at 16.5% O₂ and 4.5% CO₂, whereas conidia and MS production were maximum in normal air. Under 0.5% O₂ and 20.5% CO₂, radial growth was reduced to 17.5% of maximum and very few conidia were produced. The production of MS decreased progressively with each decrease in O₂ and corresponding increase in CO₂ concentration, and was completely inhibited at 10% O₂ and 11% CO₂. Infected tomato stems exposed to normal air, 10% O₂ and 11% CO₂, or 2.5% O₂ and 20% CO₂, produced the maximum, 10% of the maximum, and no MS, respectively. Infected stems, that were exposed to the inhibitory gas mixtures for 10 days, resumed production of MS after return to normal air, and produced within 10 days about 30-40% of the numbers of MS produced by stems exposed continuously to normal air. Exposure of cultures to ethylene concentrations ranging from 0 to 35 μliters/liter did not affect growth, sporulation, or MS production. Microsclerotia produced under the different atmospheres were equally viable. Also, MS produced under normal air, and then exposed to low O₂ and high CO₂ concentrations for up to 3 mo, survived as well as MS exposed continuously to normal air.