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Interaction Specificity of the Biocontrol Agent Sporothrix flocculosa: A Video Microscopy Study. Richard R. Bélanger, Département de Phytologie, Faculté des Sciences de l'Agriculture et de 1'Alimentation, Université, Laval, Québec, Canada G1K 7P4; James W. Deacon(2), (2)Institute of Cell and Molecular Biology, University of Edinburgh, Daniel Rutherford Building, Mayfield Road, Edinburgh, United Kingdom EH9 3JH. Phytopathology 86:1317-1323. Accepted for publication 13 August 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-1317.

Sporothrix flocculosa, a biocontrol agent reported to act by antibiosis, had a differential effect against four target fungi, based on video microscopy records of the interactions. Two of the fungi, Botrytis cinerea and Cladosporium cucumerinum, were very susceptible and reacted ahead of the advancing colony of S. flocculosa. Typical reactions included retraction of the plasmalemma, aggregation of the cytoplasm, and cell death. When S. flocculosa was inoculated directly onto a colony of B. cinerea, conidia of the biocontrol agent developed toward the pathogen, and the hyphae of B. cinerea ceased cytoplasmic activity and became highly vacuolated within 8 h. Individual conidia of S. flocculosa produced several germ tubes, but did not attack live, necrotic, or dead hyphae of the pathogen. The other two tested fungi, Fusarium oxysporum f. sp. radicislycopersici and Idriella bolleyi, were unaffected by the presence of S. flocculosa. These results correlated with previous observations that C. cucumerinum and F. oxysporum f. sp. radicis-lycopersici were, respectively, sensitive and tolerant against purified toxins of S. flocculosa. This indicates that the host range of S. flocculosa is dictated by host sensitivity to its toxins.

Additional keywords: biological control, host specificity.