Disease Note

Head Rot of Broccoli in Victoria, Australia, Caused by Pseudomonas marginalis. D. L. S. Wimalajeewa, Plant Research Institute, Burnley, Victoria 3121, A. C. Hayward, Department of Microbiology, University of Queensland, St. Lucia 4067, and T. V. Price, School of Agriculture, La Trobe University, Bundoora, Victoria 3083, Australia. Plant Disease 69:177, 1985. Accepted for publication 17 October 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-177e.

Head rot of broccoli (dark water-soaked areas that later rot and turn black) was first reported in Victoria in 1978.  The disease occurs during cool, moist weather, with losses in the field averaging 35%.  The disease, which also occurs elsewhere in Australia and in some other countries, was originally shown to be caused by Erwinia carotovora (Jones) Bergey et al.; this is considered incorrect because E. carotovora reproduced symptoms only when heads were wounded.  In autumn 1984, a fluorescent pseudomonad was isolated from broccoli head (cv. Skiff) showing incipient water-soaking.  In field tests, 92% of 200 uninjured plants spray-inoculated with the isolated bacterium (10⁸ cells/ml) developed head rot within 5 days, whereas 200 control plants similarly treated with water remained symptomless.  The bacterium was reisolated and pathogenicity again confirmed on 100 plants of two other broccoli cultivars (Bravo and Premium Crop).  The pathogen has been identified as a highly pectolytic strain of Pseudomonas marginalis (Brown) Stevens.