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Ecology and Epidemiology

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.