VIEW ARTICLE

Ecology and Epidemiology

Effects of Oxygen, Carbon Dioxide, and Ethylene on Growth, Sclerotial Production, Germination, and Infection by Sclerotinia minor. E. D. Imolehin, Research assistant, Department of Plant Pathology, University of California, Davis 95616; R. G. Grogan, professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 70:1158-1161. Accepted for publication 19 May 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-1158.

At O₂ concentrations ranging from 4 to 21% (normal air) with CO₂ nearly constant at 0.03%, in vitro differences in radial growth or sclerotial production by S. minor were not significant, but at O₂ concentrations below 4% both parameters were greatly reduced. Sclerotial production was more sensitive to O₂ concentrations below 4% than was radial growth. At concentrations of CO₂ ≥ 8% with O₂ kept at about 21%, both mycelial growth and sclerotial formation were reduced, but sclerotial formation was more sensitive to high levels of CO₂ than was radial growth. Germination of sclerotia increased with increasing O₂ concentrations between 1% and 8% with CO₂ kept nearly constant at 0.03%, but there were no significant differences in germination at O₂ contents ranging from 8 to 21%. With O₂ nearly constant at 21% there was a significant reduction in sclerotial germination at about 20% CO₂ but not at lower concentrations of CO₂. In the various O₂–CO₂ gas mixtures, sclerotial germination was similar to that obtained with similar levels of CO₂ when CO₂ levels alone were increased. No germination occurred in 19% CO₂ and 2% O₂. Results of in vitro tests with different combinations of concentrations of O₂ and CO₂ on infection of lettuce tissue by sclerotia indicated that O₂ concentrations of 7.8% and above were more favorable for infection than lower concentrations, and CO₂ concentrations ≥ 12.3% were less favorable than lower concentrations. Percent infection of lettuce tissues by sclerotia was less at the respective O₂ and CO₂ levels than was infection by mycelial disks. These results indicate that restriction of infection to lettuce tissues at or near the soil surface is not due to impaired aeration at the greater soil depths.