JOURNAL OF THE SCIENTIFIC AGRICULTURAL SOCIETY OF FINLAND Maataloustieteellinen Aikakauskirja 345 Voi. S4: 345-356, 1982 The suppressiveness of Finnish light coloured Sphagnum peat RISTO TAHVONEN Department ofPlant Pathology, University ofHelsinki SF-00710 Helsinki 71, Finland Abstract: Half of the Sphagnum peat lots used as the substrate significantly reduced or inhibited damping-off caused by Altemaria brassicicola Wiltshire, Plenodomus lingam (Tode ex Fr.) Höhnel and Rhizoctonia solani Kuhn on cauliflowers. New peat sloweddown the spread of Fusarium oxysporum Schl. f. sp. lycopersici (Sacc.) Snyder & Hansen from infected tomato plants to healthy ones and development of the disease on infected seedlings in comparison to disinfected peat. When new peat was added to disinfected peat the suppressing effect was regained. The most common microbes in the peat were bacteria, Streptomyces spp., followed by fungi, Penicillium spp., Mortierella spp. and Trichoderma viride Pers. ex Fr. Strepromyces spp. and T. viride effectively inhibited the growth of a number of soil and seed- borne fungi on a nutrient medium. Treating the peat or seeds with T. viride and Streptomyces spp, isolates inhibited or reduced damping-off caused by A. brassicicola, P. lingam and R. solani on cauliflower growing on the peat substrate. Introduction Light-coloured Sphagnum fuscum peat is the most common substrate used in greenhouse cultivation in Finland. The structural, physical and chemical properties of this type of peat make it an ideal growing medium for plants. The peat research carried out by Prof. PUUSTJÄRVI (1973) has resulted in peat cultivation becoming well established and the programmed growing of a number of crop plants has already become quite developed (PUUSTJÄRVI 1977). New peat is known to be free from plant pathogens and pests, which in many cases has been the deciding factor for the success of such a type of cultivation. It has even been shown that peat inhibits the spreading of plant pathogens from infected to healthy plants (PUUSTJÄRVI 1974). The fact that peat is an organic substrate enables it to support a high level of microbial activity and its microflora is characterised by large numbers of bacteria, Actinomycetes and fungi but a relatively small number of individual microbial species (ALEXANDER 1961, CHRISTENSEN and WHITTINGHAM 1965, HOLD- ING et al. 1965). The high level of microbial activity in fertilized and limed https://www.c-info.fi/en/info/?token=o9uRRCow7TSaqJVk.QJx9ClTWLoTfTxaxICx7Tw.EBzSdlJf3hhlYfB3P8_6O1OvqFxge2zgaeCIk1RKsuftiUiqHoed521KZJUEJawDubS_dV4_QMh66bLJBgLETLG6dRO09W3MKTfJfQr1RLh7HyvmR2ZmvVquvxEDeo6ZYzcV6mmQgiBCsDYmxvz46KY-BU1xATCD8nzmxg 346 peat, as well as the presence of certain chemical compounds such as phenols, are presumably the main reason for the ability of peat to suppress fungal pathogens. It has been known for a long time that mineral soil is capable of suppressing fungal pathogens (BAKER and COOK 1974, BAKER 1981), but the information about peat in this respect is sparse and partly contradictory (WATSON and FORD 1972, CHINN 1967). It was found in some experiments carried out at the Department of Plant Pathology, the University of Helsinki, that the presence of seed-borne pathogens on cruciferous plants, even in large numbers, was of little practical significance when the plants were growing on new peat (TAHVONEN 1979). Following these observations, a number of studies were started to investigate the capacity of light-coloured Sphagnum peat to suppress fungal pathogens. The aim was to determine the extent and significance of this phenomenon in peat cultivation and the possible causes of the phenomenon. Material and methods Unless otherwise stated, the peat used in these experiments was ST-400 A 0 peat supplied by Satoturve Oy. The sample lots obtained from different peat producers which were included in the experiments are listed inFigures 1 and 2. The peat was limed with dolomite limestone (10 kg/m3 ) and fertilized with basic fertilizer (N-P-K: 17-9-14, and micronutrients) 1.5 kg/m3 in the seedling growing experiments and 2 kg/m 3 in the tomato experiments. Cauliflower seed was used in the seedling growing experiments in which the pathogen suppressiveness of different peat lots was tested. The seeds were artificially infected with Alternatia brassicicola Wiltshire, Plenodomus lingam (Tode ex Fr.) Höhnel or Rhizoctonia solani Kiihn. The test fungi were grown on PDA medium for about 10 days and then scraped off into distilled water at a level of 1 petri dish/100 ml. The seeds were soaked in the suspension for 5 minutes and then dried overnight between sheets of filter paper. The peat used in the experiments on tomato wilt disease caused by Fusarium oxysporum Schl. f. sp. lycopersici (Sacc.) Snyder & Hansen was disinfected by steaming at 100°C for 1 hour and then adding 0, 10, 25 or 50 % new, non-disinfected peat to the steamed peat after it had cooled down. Fertilization and liming were carried out after the peat had been disinfected. Each sample block consisted of a basin, 1.4x1.6 m in size, containing 400 1 of peat and separated from the other blocks and sub-soil by plastic sheeting. Each block was planted with two rows of four seedlings. 20 ml of a suspension of F. oxysporum f. sp. lycopersici (at a concentration of one PDA petri dishfull/100 ml) was pipetted into the bottom of the planting holes in one of the rows during planting out. A 2 cm-thick layer of non-infected peat from the same block was placed in the planting holes on top of the suspension. The seedlings were then planted in the normal way. Dead plants were removed during the course of the growing season and, at the end of the experiment, samples of plant tissue were removed from the stems of plants lacking leaf symptoms, at a height of 10 cm above the ground. The tissue 347 samples were incubated on PDA medium in order to test for the presence of Fusarium infection. In 1977-78 the tomato seedlings were planted out immediately after the peat substrate had been treated, but in 1979 greenhouse cucumbers were grown on the peat for 4 months before planting out the tomato plants. The peat substrate was not subjected to any treatment at all when the plant coverage was changed. The tomato variety ”Rimset” was used in the experiments. The seedlings were grown, irrigated, fertilized and otherwise tended using the cultivation techniques approved in Finland for peat culture. The experiments were carried out with three replications. The microflora of the peat was determined in 1975 by homogenising the peat in sterile water at levels of lof 5 g/100 ml. Dilutions (1CT 1 to 10'6 ) were then made and 1 ml and 10 ml pipetted into cooled (40°C) PDA medium. After mixing the agar was poured into three petri dishes. Determinations were made on 7 peat lots. In 1979,25 %of the water in the PDA medium was substituted by an extract made by compressing peat of normal cultivation moisture content at a pressure of about 200 atmos. Two selective media were prepared from this nutrient medium. One of them contained 10 ppm of prothiocarp fungicide (Previcur N) and 400 ppm of streptomycene, and the other 10 ppm prothiocarp fungicide and 5 ppm benomyl (Benlate). One gramme of peat was homogenised in 99 ml of water and aliquots of the 10'2-10'7 dilutions pipetted into the cooled-down media and then poured into three petri dishes. As this method was found to be very time-consuming, determinations were made on one peat lot only which had been stored in different ways: dry peat, fertilized peat at normal moisture content and peat used as the substrate for the tomato plants. The same peat lots were also used in the seedling growing experiments. Samples were taken from the different peat lots at monthly intervals over a period of three months (14.4.-13.7.). The microflora determinations carried out in 1975 were mainly concerned with determining the fungi present in the peat. Of the bacteria, only Streptomyces spp. were investigated. The experiments carried out in 1979 were designed to determine the variations in different micro-organisms during storage and cultivation. The results obtained in this study concerning the numbers of micro-organisms are only relative values and can only be used as supportive evidence because only two of the samples'had duplicates and the results are to a great extent dependent on the type of method used in the determinations. A number of the bacteria and fungi (Table 1) isolated from the peat were tested against the most common fungalpathogens on PDA medium (Tables 1 and 2). This was done by transferring the microbe isolated from the peat to four points around the edge of the petri dishes and the test pathogen to the centre of the dish. These tests were carried out in triplicate. The microbes found to be most effective on the nutrient medium were tested for suppression of damping-off in seedling growing experiments. In 1975, a suspension of Trichoderma viride Pers. ex Fr. (1 petri dish/100 ml) was added to the peat at a concentration of 1.5 1 of suspension/15 1 autoclaved peat five days before sowing. Cauliflower seeds inoculated with A. bras- sicicola, P. lingam or R. solani (see p. 00) were sown in new and disinfected peat and peat inoculated with T. viride with four replications. In the experiment carried out in 1979, seeds infected with A. brassicicola and R. solani were treated by immersing them in suspensions (1 petri dish/100 ml H2 O) prepared using 4 Streptomyces spp. isolates and 3T. viride isolates. The seeds were sown in steam-disinfected peat after being dried. The results are expressed as the percentage of healthy seedlings out of the number of seedlings sown. Results Capacity of light-coloured peat to suppress fungal pathogens The peat lots from different sources exhibited variation in their capacity to suppress damping-off fungi. In the tests carried out in 1975, the peat lots obtained from Leivonmäki and Metsämaa effectively suppressed damping- off caused by Rhizoctonia solani Kiitin and Plenodomus lingam (Tode ex Fr.) Höhnel on cauliflower in comparison to the other peat lots (Fig. 1). Simi- larly, in the tests carried out in 1979 (Fig. 2) unconstituted peat from Satoturve, samples from Eurajoki and the peat lot from Hartola were effective against damping-off caused by Alternaria brassicicola Wiltshire in comparison to the other peat lots tested. Peat fertilized with basic fertilizer and stored for 2 months at normal moisture content also suppressed damping-off caused by A. brassicicola. The Fig. 1. Effect of peat lots from different sources on damping-off caused by Rhizoctonia solani and Plenodomus lingam on caulif- lower after the seedlings had been grow- ing for 3 weeks. Peat source: 1 = Kon- tiolahti, 2 = Metsämaa, 3 = Luumäki, 4 = Eurajoki, 5 = Leivonmäki, 6 = Pyl- könmäki. Fig. 2. Effect of peat source and pretreatment on damping-off caused by Rhizoctonia solani and Plenodomus lingam on cauliflower af- ter the seedlings had been growing for 3 weeks. Source of peat and pretreatment: 2 = Satoturve Oy St-400 AO, 3 = Eurajoki, 4 = Eurajoki, 5 = Hartola, 6 = Haapavesi, 7 = Lappeenranta, 8 = Karttula, 9 = Sompaneva, 10 = Peräseinäjoki, 11 = peat used for growing tomatoes, 12 = fertilized peat kept moist, 13 = steam-sterilisedpeat. 348 349 capacity of the peat used as the substrate for the tomato plants to suppress fungal pathogens increased so strongly that the incidence of damping-off caused by A. brassicicola was only 13 % and that of damping-off caused by R. solani 30 %. Almost all the seeds growing in steam-sterilised peat and in peat lots with a weaker suppressiveness died (Fig. 2). Wilt disease caused by Fusarium oxysporum Schl f. sp. lycopersici (Sacc.) Snyder & Hansen on tomato plants spread in 1977 to a considerably smaller extent from infected tomato plants to adjacent rows when growing in new peat than in steam-sterilised peat (Fig. 3). Although cucumber plants had been grown on the steam-sterilised peat for four months, the capacity of the peat to suppress fungal pathogens had not recovered to anywhere near the level exhibited by new peat (Fig. 4). The infected seedlings also died off at a slower rate in new peat than in steam-sterilised peat (Figs. 3 and 4). The suppressiveness of the substrate returned to the level for new peat when either 25 % or 50 % new peat was added to the steam-sterilised peat (Figs. 3 and 4). The peat used in the tomato experiment in 1978 was not able to suppress Fusarium wilting disease to any significant extent (Fig. 3). The microflora present in the peat The following micro-organisms were identified in the peat lots: Bacteria Eubakteriales unidentified bacteria Actinomycetales Streptomyces spp. Fungi Zygomycetes Absidia sp. Mortierella spp. Mucor sp. Piptocephalis sp. Ascomycetes Sordaria spp. Deuteromycetes Ascochyta sp. Aspergillus spp. Aureobasidium pullulans Arnaud Chrysosporium sp. Goidaniehella scopula Arnaud Hughesiella sp. Oidiodendron rhodogenum Robak Penicillium spp. Rhodotorula sp. Thermomyces sp. Trichoderma viride Pers. ex Fr. Unidentified fungi producing mycelia 350 Fig. 3. The spread of Fusarium oxys- porum f. sp. lycopersici from inoculated tomato plants to plants in the adjacent row by the end of the growing season and the mortality rate of in- oculated plants on peat subs- trates to which different amounts of new peat were added after steam-sterilisa- tion. Fig. 4. The spread of Fusarium oxys- porum f. sp lycopersici from inoculated tomato plants to plants in the adjacent row by the end of the growing season and the mortality rate of in- oculated plants on peat subs- trates to which different amounts of new peat were added after steam-sterilisa- tion. Cucumbers were grown on the substrate for four months before planting the tomatoes. The most common organisms isolated from the peat were bacteria, Streptomyces spp., Penicillium spp., Mortierella spp. and T. viride. Changes occurred in the composition of the microflora and in the numbers of individual organisms during storage and cultivation. The number of bacteria in new, unfertilized peat varied from 5T08 to 1.5T0 9 bacteria/g. Peat fer- tilized with basic fertilizer and stored at normal moisture content contained 610 10-1.310" bacteria/g and peat used for growing tomato plants 21011—4-10" bacteria/g. The numbers of Penicillium spp. in new peat were 5-12-108/g, in peat stored moist 4-10 7-8-10 10/g and in peat where tomatoes had been grown l-6T06/g. The numbers of T. viride in the different peat lots varied between 5-106 and 4-IOVg. There was considerable variation in the numbers of Streptomyces spp. They were not found at all in the peat stored at normal moisture content, the number of spores in the peat used for growing tomatoes varied from 5107 to 4-108/g in the first and last plate count and in the dry peat the number of spores was 3107/g in one plate count. The numbers of Mortierella spp. varied from 3106-5T0 8/g. The effect of peat micro-organisms on fungal pathogens Of the different microbes isolated from the peat samples, the T. viride and Streptomyces spp. isolates suppressed, extremely effectively, the growth of Fusarium oxysporum, Rhizoctonia solani and Pythium debaryanum auct. non Hesse on the nutrient medium (Table 1). In additional tests, the Streptomyces spp. isolates were also effective against A. brassicicola, F. culmorum (W.G. Smith) Sacc., F. sulphureum Schlechtendahl, Helminthos- porium sativum Pammel, King & Bakke, Phoma exigue Desm. var . foveata (Foister) Boerema, P. exique Desm. var. exique Maas, and Whetzelinia sclerotiorum (Lib.) Korf & Dumont (Table 2, Figs. 5 and 6). In the prelimi- nary tests carried out in 1975, three of the bacterial isolates from the peat suppressed the growth of Fusarium to a moderate extent, but in the tests Table 1.The suppressive effect of microbes isolated from peat against different fungi growing on nutrient medium. Fusarium oxysporum Rhizoctonia solani Pythium debaryanum Microbe and number of isolates = ineffective, (+) = medium strong, + = strong (+) + - (+) + (+) + Bacteria, 10 10 0 0 3 0 7 0 1 0 0 1 0 0 1 5 10 0 0 3 2 5 0 1 0 1 0 0 0 0 6 10 0 0 3 3 4 0 1 0 1 0 o 0 1 5 Streptomyces spp., 10 Penicillium spp., 1 Sordaria sp., 1 Trichoderma viride, 6 Unidentified, mycelium- forming fungi, 6 6 0 0 6 0 0 6 0 0 351 Table 2. The suppressive effect of certain Streptomyces isolates against different fungi growing on nutrient medium. Test fungus Streptomyces isolate 1 2 3 7 21 = ineffective, (+) = medium strong, and + = strong suppressive effect Altemaria hrassicicola + + + + + Fusarium avenaceum (+) (+) + F. culmorum (+) (+) + (+) (+) F. oxysporum + F. sulphureum + + + + + Fielminthosporium sativum + + + + + Phoma exigue v. foveata + + + + + P. exigue v. exigue + + + Rhizoctonia solani (+) (+) (+) Whetgelinia sclerotiorum + + + + + Fig. 5. Effect of Streptomyces sp. on different fungal pathogens growing on PDA medium. Top and bottom row = control petri dishes, middle rows = as the other rows except Streptomyces isolates transferred to four points at the edge of the dishes. 1 = Fusarium oxysporum, 2 = F. culmorum, 3 = F. avenaceum, 4 = Flelminthosporium sativum, 5 = Rhizoctonia solani, 6 = Whetzelinia sclerotiorum, 7 = Alternaria brassicicola, 8 = Phoma exigue v. exigue, 9 = P. exigue v. foveata. 352 Fig. 6. Effect of Streptomyces sp. on the growth of Pythium debaryanum on PDA medium. Control dish on the left and a dish with Streptomyces isolates transferred to four points at the edge of the dish on the right. Fig. 7. Effect of inoculating the growing subs- trate with Trichoderma viride five days before sowing on damping-off caused by Rhizoctonia solani, Alternaria brassicico- la and Plenodomus lingam on caulif- lower. Fig. 8. Effect of treating seeds with Streptomy- ces sp. and Trichoderma viride isolates on damping-off caused by Alternaria brassicicola and Rhizoctonia solani on cauliflower. 353 354 carried out in 1979 all the ten isolates tested were ineffective (Table 1). Similarly, all the unidentified, mycelium-forming fungi (6 in all) were ineffective. T. viride reduced or significantly suppressed damping-off caused by Rhizoctonia, Alternaria and Plenodomus on cauliflower growing in steam- sterilised peat (Fig. 7). When the ability of four Streptomyces spp. and three T. viride isolates to suppress damping-off in peat caused by Alternaria and Rhizoctonia were compared, the seeds being treated with suspensions of the isolates, all the treatments significantly improved seedling emergence, but only the Streptomyces treatment gave any long-term protection against damping-off (Fig. 8). Discussion The capacity of light-coloured Sphagnum peat to suppress fungal patho- gens is analogous to that which has been observed on numerous occasions in other types of substrate (BAKER and COOK 1974, BAKER 1981). Disease suppression effects have also been found in peat soils (CHINN 1967). As far as is known, however, this phenomenon has not been studied in Sphagnum fuscum peat. The suppressiveness of the different peat lots varied to a very great extent: in some lots there was no suppressive effect while other lots were very effective suppressors of damping-off. This would explain the differences obtained in the tomato wilting disease experiments in different years. No differences were found in the structure or composition of the peat lots which would have accounted for the variations in the suppressive capacity of the peat lots. Disinfecting the peat by steaming or autoclaving it almost completely eliminated the suppressive effect (cf. LIU and BAKER 1980, SCHER and BAKER 1980). This suggests that suppression is of microbiological origin. Chemical compounds, such as phenols, or microbial remains in the peat may possibly have a slight suppressive effect on fungal pathogens after steam disinfection, as has been observed in an earlier study (TAHVONEN 1979). The differences in the supressiveness of the different peat lots can most naturally be explained by variations in the microbial population. The num- bers of Penicillium spp. and Trichoderma viride Pers. ex Fr. varied consider- ably in all of the peat lots. These are known to be strong competitors and producers of antibiotics (BAKER and COOK 1974). However, the greatest variations occurred in the numbers of Streptomyces spp., which surely has a significanteffect on the variation in the suppressive effect of the different peat lots. For example, peat lot No. 11 contained very large numbers of Strep- tomyces spp. spores in comparison to lots No. 2 and 12, which did not suppress damping-off caused by Rhizoctonia solani Kiihn at all (Fig. 2). The Streptomyces species found in the soil are known to be prolific producers of antibiotics (ALEXANDER 1961). The capacity of peat to suppress fungal pathogens can be utilised fairly effectively in reestablishing the suppressive effect in disinfected peat. It has 355 earlier been very common to add new peat as an ameliorator before steam- sterilisation and this has obviously destroyed the beneficial microbes. If peat is added after disinfection, then the suppressive effect is almost completely regained (cf. SCHER and BAKER 1980). The adoption of this method also seems to be necessary because, according to the results of these experiments, the suppressive effect of disinfected peat is not regained without the addition of new peat, even when cultivated for a long time. However, the beneficial effect of adding peat is not always completely certain because the suppressive effect of certain peat lots are as bad as steam-disinfected peat even. The microbes isolated from the peat lots, especially T. viride and Strep- tomyces spp., were extremely effective antagonists on the nutrient medium against all the fungal pathogens tested. These microbes are known to be effective competitors and/or producers of antibiotics (BAKER and COOK 1974). In preliminary biological control experiments, both Streptomyces spp. and T. viride suppressed or reduced damage caused by damping-off fungi in peat. This suggests that there are good possibilities of achieving biological control of plant pathogens in disinfected peat substrates at least, or even in new peat which has no natural suppressive effect of any importance. Acknowledgements: The peat lots used in the experiments were supplied by members of the Finnish Peat Producers Association. Pirkko Harju, Kaija Karhunen and Olli Reinikainen have taken part in the practical realisation of the experiments. Lahja Pesonen, Pentti Heinänen and Tauno Koivunen, staff members of the Department of Plant Pathology, have assisted in establishing and carrying out the experiments. The salaries of part of the support personnel have been paid by Kemira Oy. 1 extend my sincere thanks to all the above-mentioned for their help and assistance. References ALEXANDER, M. 1961. Introduction to soil microbiology, 472 p. New York. BAKER, K. F. 1981. Biological control. Fungal wilt diseases of plants, p. 524-561. New York. & COOK, R. J. 1974. Biological control of plant pathogens. 433 p. San Francisco. CHINN, S. H. F. 1967. Differences in fungistasis in some Saskatchewan soils with special reference to Cocliobolus sativus. Phytopath. 57: 224—226. CHRISTENSEN, M. & WHITTINGHAM, W. F. 1965. The soil microfungi of open bogs and conifer swamps in Wisconsin. Mycol. 57: 882-896. DALE, E. 1914. On the fungi of the soil. Ann. Mycol, 12: 33-62. HOLDING, A. J., FRANKLIN, D. A. & WALTING, R. 1965. The microflora of peat-podsol transitions. J. Soil Sci. 16: 44—59. LIU, S-D. & BAKER, R. 1980. Mechanism of biological control in soil suppressive to Rhizoctonia solani. Phytopath. 70: 404—412. PUUSTJÄRVI, V. 1973. Kasvuturve |a sen käyttö. 172 p. Helsinki. 1974. Turve antiseptisenä aineena. Puutarha 77: 331-332. 1977. Ohjelmoitu turveallasviljely. Puutarhakalenteri 36: 237—255. SCHER, F. M. & BAKER, R. 1980, Mechanism of biological control in a Fusarium -suppressive soil. Phytopath. 70: 412-417. TAHVONEN, R, 1979. Seed-borne fungi on cruciferous cultivated plants in Finland and their import- ance in seedling raising. J. Scient. Agric. Soc. Finl. 51: 327-379. WATSON, A. G. & FORD, E. J. 1972.Soil fungistasis- a reappraisal. Ann. Rev. Phytopath. 10: 327-348, Ms received October 29. 1982. 356 SELOSTUS Vaalean rahkaturpeen sienitautien estovaikutus Risto Tahvonen Helsingin yliopiston kasvipatologian laitos, 00710 Helsinki 71 Suomessa on kasvihuoneviljelyssä vaalea rahkaturve yleisin kasvualusta, jolla on todettu olevan kasvin kannalta hyvien fysikaalisten ja kemiallisten ominaisuuksien lisäksi estovaikutusta alustassa leviäviä sienitauteja vastaan. Tämän ilmiön selvittämiseksi järjestettiin vuosina 1975-79 kokeita Helsingin yliopiston kasvipatologian laitoksella. Eri turvetuottajilta saatiin turve-eriä testettavaksi. Viljelykokeissa käytettiin Satoturve Oy:n ST-400 AO -turvetta. Sienitautien estovaikutusta mitattiin kylvämällä peruslannoitet- tuihin ja kalkittuihin turve-eriinAltemaria brassicicola Wiltshire -, Plenodomus lingam (Tode ex Fr.) Höhnel - ja Rhizoctonia solani Kiihn -sienellä saastutettuja kukkakaalin siemeniä. Uusien turve-erien lisäksi kokeissa oli mukana myös höyrytettyä turvetta. Ilmiön merkitystä pitempiaikaisessa viljelyssä kuin taimikasvatuksessa tutkittiin. Kasvualustana käytettiin uutta turvetta ja höyrytettyä turvetta, johon oli lisätty höyrytyksen jälkeen uutta turvetta 0, 10,25 ja 50 % tilavuudesta. Koeruudussa toinen tomaattirivi saastutettiin istutuksen yhteydessä Fusarium oxysporum Schl. f. sp. lycopersici (Sacc.) Snyder & Hansen -lakastumistautisienellä. Turve-erien mikrobeja ja niiden runsauksia määritettiin. Yleisimpien mikrobien vaikutus tärkeimpiin sienitauteihin testattiin ravintoalustalla. Trichoderma viride Pers. ex Fr. - ja Streptomyces spp. -isolaatteja kokeiltiin kukkakaalin taimipoltteen torjunnassa. Noin puolet tutkituista turve-eristä vähensi voimakkaasti tai esti lähes kokonaan kuk- kakaalin taimipoltteen verrattuna huonoimpiin eriin tai höyrytettyyn turpeeseen. Uudessa turpeessa tomaatin /«stfn«w-lakastumistauti tappoi kasveja hitaammin ja vähensi taudin leviämistä terveisiin kasveihin verrattuna höyrytettyyn turpeeseen. Tulos oli samanlainen, vaikka esikasvina oli ollut neljä kuukautta kurkku. Kun höyrytettyyn alustaan lisättiin 25 % tai 50 % uutta turvetta, kasvualustan taudinestovaikutus palautui. Turpeen yleisimpiä mikrobeja olivat bakteerit, Streptomyces spp. sekä sienet Mortierella spp., Penicillium spp. ja T. viride. Streptomyces spp. ja T. viride estivät ravintoalustalla F. oxysporum, R. solani ja Pythium debaryanum auct. non Hesse -sienten kasvun. Lisätestauk- sissa Steptomyces spp. -isolaatit estivät tehokkaasti edellisten lisäksi A. brassicicola, F. avenaceum Sacc., F. culmorum (W. G. Smith) Sacc., F. sulphureum Schlechtendahl, Helmin- thosporium sativum Pammel, King ex Bakke, Phoma exigue Desm. v. foveata (Foister) Boerema, P. exigue Desm. v. exigue Maas. ja Whetzelinia sclerotiorum (Lib.) Korf. ex. Dumont -sienten kasvun ravintoalustalla. Alustavissa taimikasvatuskokeissa T. viride torjui maahan lisättynä Rhizoctonia- ja vähensi Altemaria- ja Plenodomus-tzitmpohexxz kukkakaalilla. Neljää Streptomyces spp. ja kolmea T. viride -isolaattia verrattiin siemenkäsittelynä kukkakaalin taimipoltteen torjumiseksi. Käsit- telyt paransivat merkitsevästi taimettumista, mutta Streptomyces-käsittelyt antoivat pitem- piaikaisen suojan taimipoltetta vastaan kuin T. viride -käsittely.