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Disease Control and Pest Management

Interactions Between Bacteria and Trichoderma hamatum in Suppression of Rhizoctonia Damping-off in Bark Compost Media. O. C. H. Kwok, Postdoctorate, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691; P. C. Fahy(2), H. A. J. Hoitink(3), and G. A. Kuter(4). (2)Former visiting scientist, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691; Present address: BCRI, Dept. Agric., PMB 10, Rydalmere, NSW, 2116, Australia; (3)Professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691; (4)Former postdoctorate, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691, Present address: Director of Research and Development, Earthgro, Inc., Route 207, Box 143, Lebanon, CT 06249. Phytopathology 77:1206-1212. Accepted for publication 2 March 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1206.

Eight species of bacterial antagonists, including Bacillus cereus, Enterobacter cloacae, Flavobacterium balustinum, Janthinobacterium lividum, Pseudomonas fluorescens biovar III, P. putida, P. stutzeri, and Xanthomonas maltophilia, induced suppression to Rhizoctonia damping-off in container media amended with composted hardwood tree bark. Combinations of some of the strains of bacterial antagonists, E. cloacae 313, F. balustinum 299, P. fluorescens biovar V A1, P. putida 371, or P. stutzeri 280, with Trichoderma hamatum 382 were consistently more effective than the fungal isolate alone. Other isolates, for example P. fluorescens biovar V A1 and A498, were not effective unless combined with T. hamatum 382. Spontaneous rifampicin-resistant mutants of F. balustinum, P. putida, and X. maltophilia colonized both cucumber roots and the conducive container medium to high population levels in irrigated pots. Without irrigation, root colonization was less extensive, and colonization of the container medium was limited to the area surrounding the treated seed. Population levels established were highest in the autoclaved container medium and lowest in the suppressive medium already colonized by a mesophilic microflora. We concluded that suppression of Rhizoctonia damping-off in the naturally suppressive container medium may be due to the activity of a variety of antagonists.