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Antifungal Substances Produced by Penicillium frequentans and Their Relationship to the Biocontrol of Monilinia laxa. A. De Cal, Department of Plant Pathology, E.T.S. Ingenieros Agrónomos, Madrid, Spain; E. M.-Sagasta, and P. Melgarejo. Department of Plant Protection, C.I.T.-I.N.I.A., Madrid, Spain. Phytopathology 78:888-893. Accepted for publication 16 December 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-888.

Antibiotic substances produced by an isolate of Penicillium frequentans, a component of the resident mycoflora of peach twigs previously found to antagonize Monilinia laxa, were produced in potato-dextrose broth and isolated and partially purified from the cell-free medium by liquid:liquid partitions. Two active substances were partially characterized by thin-layer chromatography, infrared absorbance, and qualitative analysis and were named antibiotic A and antibiotic B. Both antibiotics were active against a wide range of plant pathogenic fungi including M. laxa and several components of the mycoflora of peach twigs. The ED50 values for the germination of spores and the germ tube growth of M. laxa were 0.31 mg/ml and 0.02 mg/ml, respectively, for antibiotic A and 4.84 mg/ml and 0.13 mg/ml, respectively, for antibiotic B. Both antibiotics were temperature-stable, while the activity of antibiotic A was lowered at basic pH. Antibiotic B was also more stable over time at room temperature than antibiotic A, conserving 30% of its activity against the germ tubes of M. laxa after 70 days. Both antibiotics showed significant inhibition (p ≤ 0.05) of M. laxa on peach twigs.

Additional keywords: antibiosis, brown rot disease, competition, phyllosphere.