Effect of Controlled Oxygen and Carbon Dioxide Atmospheres on Bacterial Growth Rate and Soft Rot of Tomato Fruits Caused by Pseudomonas marginalis. S. N. Ibe, Department of Biological Sciences, University of Lagos, Akoka, Lagos, Nigeria. R. G. Grogan, Professor, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 67:1005-1008. Accepted for publication 16 March 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1005.

A gas mixture composed of 4% O₂, 2% CO₂, and 94% N₂ (O₂:CO₂ ratio of 4:2) reduced in vitro growth of Pseudomonas marginalis during the 36-hr incubation period at 12.5 C to 47% of that in air (21:0.03). At controlled atmospheres (CAs) of 4:0, 4:10, and 1:2, growth was reduced further to 36, 33, and 16% of the control, respectively. With P. fluorescens, overall growth was faster but was also reduced at CAs of 4:0, 4:2, 4:10, and 1:2 to 55, 54, 30, and 17% of the control in air. In ripe tomato fruits inoculated with P. marginalis and incubated in CAs of 4:0, 4:2, 4:10, and 1:2 and air, only CAs of 4:10 and 1:2 significantly reduced the percentage and severity of decay by the end of a 14-day storage at 12.5 C from that in air, but fruits were softened under these CAs. It is suggested, therefore, that tomato fruits be stored at 12.5 C under a CA of 4% O₂, 0% CO₂, and 96% N₂ to reduce physiological softening and bacterial soft rot by P. marginalis.