Biological Control of Wood-Attacking Fungi Using Bacteria

Transcription

1 BIODETERIORATION RESEARCH 3: Plenum Press, New York, 1990 In: Llewellyn, Gerald C.; O Rear, Charles E., eds. Biodeterioration Research 3: Proceedings of the 3d meeting of the Pan American Biodeterioration Society; 1989 August 3-6; Washington, DC. New York: Plenum Press; 1990: Biological Control of Wood-Attacking Fungi Using Bacteria RIANA BENKO*, Visiting Scientist from Ljubljana, Yugoslavia, and TERRY L. HIGHLEY, USDA, Forest Service, Forest Products Laboratory 1 Gifford Pinchot Drive, Madison, WI, , USA One INTRODUCTION Soon after felling, wood is susceptible to colonization by wood-attacking fungi. Infection often occurs within a few days after cutting and may continue to progress in the wood, even though the wood is processed into preservative-treated products, such as poles, railroad ties, and construction timbers. The protection of unseasoned timbers against wood-attacking fungi should not be neglected, because the quality and durability of wood products depend on good care of the unseasoned timbers. Pentachlorophenol formulations have traditionally been used to protect unseasoned timbers but environmental concerns have severely curbed the use of this material. Furthermore, the usc of chemical preservatives for such a short period as unseasoned timber requires (usually 4 to 6 months) is expensive. These objections may be overcome by using biological control agents, which are now being seriously considered for wood protection. Results have been sufficiently promising in previous studies using bacteria to control sapwood inhabiting fungi to warrant further study (Benko, 1988, 1989; Bernier et. al., 1986). In this study, we report on the effectiveness of bacteria as biological control agents against blue stain and mold fungi as well as brown- and white-rot decay fungi. 1 The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on offical time, and it is therefore in the public domain and not subject to copyright. This study was done in cooperation with Oregon State University. 327

2 MATERIAL AND METHODS Test Fungi Four representative wood-attacking fungi were selected as test fungi: Postia placenta (Fries) M. Larsen et Lombard, a brown rot; Coriolus versicolor (L.ex Fr.), a white rot; Ceratocystis coerulescens (Munch) Bakshi, Screening Tests a blue stain; and Trichoderma harzianum Rifai, a mold. Before testing on wooden samples, we screened almost 100 known bacteria, which produce metabolizes suspected of being fungitoxic, and more than 100 unknown bacteria (Buchanan and Gibbons, 1774; Reiner, 1982). The antagonistic activity of bacteria towards wood-attacking fungi was determined on yeast malt agar (yeast extract 4.0 g, malt extract 10.0 g, dextrose 4.0 g, agar 20.0 g, distilled H ml). For treatment of wood blocks, we selected six bacteria as the best in controlling one or more type of wood-attacking fungus. Pseudomonas rimosus Sobin et al., St. The bacteria were cepacia (Burkholder) Palleroni and Holmes, Streptomyces chrestomyceticus Canevazzi and Scotti, rimosus forma paromomycinus Sobin et al., St. Streptoverticillium cinnamoneum forma azacoluta (Benedict et al.) Baldacci, and Xenorhabdus luminescens Thomas and Poinar. Treatment of Wood Blocks Sporulation agar (broth) (yeast extract 1.0 g, beef extract 1.0 g, tryptose 2.O g, FeS0 4 trace, glucose 10.0 g, distilled H ml), ph 7.2, was used to grow bacteria for antibiotic production. The six bacteria were separately grown on a shaker at 150 rpm (New Brunswick Scientific Co.) at room temperature for 7 days. The bacterial cultures were then centrifuged for 30 min at l,600g, and the supernatants mixed together to produce a bacterial solution, which was used for dipping wooden samples, Pinus spp. (southern yellow pine), for 1 hour. Decay and Stain Tests The treated blocks were placed on glass rods on top of mycelial mats of wood-attacking fungi, 1000 ml distilled H 2 0) in petri dishes. which covered malt agar (30 g malt, 15 g agar, The test and control samples were incubated in a dark cultivation chamber at 27 C and 70% relative humidity for 8 weeks. Weight loss in blocks was measured versicolor, and degree of staining coerulescens and Trichoderma harzianum. The degree of staining was rated as 0 = Unstained wood, no visible for Postia placenta was recorded for follows: sign of staining on and Coriolus Ceratocystis the surface. 328

3 1 = Slightly stained wood, individual tiny blue stained spots with a maximum diameter of 2 mm. 2 = Moderately stained wood, at least one-third of the surface stained or staining in lines up to one-half of the whole surface. 3 = Heavily stained wood, more than one half of the surface stained. RESULTS The average weight loss of samples treated with the bacterial solution, exposed for 8 weeks to Postia placenta, was only 0.11%, while the average weight loss of the control samples was 61.44% (Table 1). Excellent results were also obtained with Coriolus versicolor, where the average weight loss of treated samples was 0.25% and 11.82% for the control samples. Although some samples tested with the bacterial solution exposed to Ceratocystis coerulescens showed individual tiny blue stained spots, the average degree of staining was still 0. The control samples were heavily stained with an average degree of staining of 3 (Table 2). Two of the treated samples exposed to Trichoderma harzianum showed no sign of the discoloration, but others showed slight staining of wood. The average was 0 to 1, which means that occasionally tiny green stained spots occurred on the pine blocks, but not larger than 2 mm. The control samples were heavily stained over the entire surface of the samples, with an average degree of staining of 3. DISCUSSION This work demonstrates that bacteria have promise as biological control agents in wood preservation. After testing a few hundred different bacteria, we conclude that it will be very unlikely to find a single bacterium that will be effective against all the various types of wood attacking fungi. The results of our work show that to control a wider spectrum of attacking fungi, it will be necessary to use combinations of different bacteria. Furthermore, for success in the field, it would be beneficial to obtain a better understanding of biological control mechanisms so as to maximize the establishment and controlling activities of artificially applied delivery systems. 329

4 330

5 b 0 = Unstained wood 1 = Slightly stained wood 2 = Moderately stained wood 3 = Heavily stained wood 331

6 SUMMARY This paper discusses the possibilities of using bacteria for biological control of wood-attacking fungi. The following wood-attacking fungi were used: Postia placenta, a brown rot; Coriolus versicolor, a white rot; Ceratocystis coerulescens, a blue stain; and Trichoderma harzianum, a mold. A mixture of six bacteria from the genera Pseudomonas, Streptomyces, Streptoverticillium, and Xenorhabdus was strongly antagonistic against the wood-attacking fungi. Southern yellow pine (Pinus spp.) blocks treated with bacterial solution suffered less than 1% weight loss after 2 months exposure to the brown- or white-rot fungus and were almost unattached by the blue stain or mold fungus in the laboratory tests. Acknowledgments The majority of test bacteria were obtained from the U.S. Department of Agriculture, Agriculutal Research Service, Peoria, Illnois; the University of Wisconsin, Bacteriology Department, Madison, Wisconsin; and the U. S. Department of Agriculture, Forest Service, Southern Hardwood Laboratory, Stoneville, Mississippi. We express our gratitude for their time and unselfish help. This work was supported by U.S. Competitive Grant No. 87-FSTRY Printed on recycled paper