Vol. 4: 419-427. Effect of seed dressing treatment of Streptomyces grlseoviridison barley and spring wheat in field experiments Risto Tahvonen, Asko Hannukkala and Hanna Avikainen Agricultural Research Centre ofFinland, Institute ofPlant Protection, FIN-31600 Jokioinen, Finland The effect of seed dressing with the antagonist Streptomyces griseoviridis on root rots and yields of wheat and barley was studied in field experiments. In long-term field experiments, where different levels of soil-borne inoculum of root rots were maintained with different crop sequences, seed treat- ment with the antagonist increased yields slightly on average over all experimental years. However, variations between years, crops and crop sequences were considerable. The highest yield increases were in excess of 600 kg/ha, whilst treatment occasionally resulted in slight yield losses. In experi- ments in which seed naturally infested with Fusarium spp. was used, seed treatment with 5. griseo- viridis increased yields of wheat but not those of barley. Seed dressing with an organomercurial fungicide resulted in higher yield increases than the biopreparate. Key words: biological control, Bipolaris sorokiniana, Fusarium spp., Gaeumannomyces graminis, Mycostop, crop rotation, Foot and root rot diseases are a world wide prob- lem in intensive cereal crop production. In Fin- land common root rot (Fusarium avenaceum (Corda ex Fr.) Sacc., F culmorum (W. G. Sm.) Sacc., Bipolaris sorokiniana (Sacc.) Shoem.) and take-all ( Gaeumannomyces graminis (Sacc.) v. Arx & Olivier) are widespread throughout the cereal growing area (Mäkelä and Parikka 1980). Yield losses caused by common root rot may exceed up to 10% (Uoti 1976, Kurppa 1985).The damage is most severe in cereal monoculture. Dry growing seasons favour infection by Fusa- rium species (Wiese 1987). Take-all is extreme- ly damaging in cereal monoculture on light soils during wet seasons, when 90% crop losses have been reported (Yarham 1981). Common root rot fungi are seed- and soil- borne. Seed-borne inoculum can be controlled by chemical seed dressing (Uoti 1979, Kurppa 1985,Wiese 1987). There is, however, no effec- tive chemical control against soil-borne inocu- lum of common root rot and truly soil-borne take-all. Soil-borne root rots are mainly con- trolled by diverse crop rotations and other cul- tural practices (Yarham 1981, Wiese 1987). Much effort has gone into investigation of the biocontrol of soil-borne root-rots of cereals. Numerous soil-inhabiting micro-organisms, e.g. © Agricultural Science in Finland Manuscript received October 1994 419 AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=xtvSUiwr2HUp-hK5.KLbAju3HZu6FOnOv-f9-Eg.tJLXQmdqildwPkvYEdqX3uAkaaH8BW1VTaONQRQDO89eAf1F_575uzmeha5qqUgyBROD1nyM0jK0q3NYB7RuetuFMCiyt913_7xAfwl2gp1PPihhN-W4teinIjQOMyn_NDKkAy4qbLN9e5q-xlPZUFwz1R2oK0SInajWyc6CWJ4wHNHSRR4FqGrNnWhvyEWqRU4O_rCjSOflJgINmydicwd8vL-T2B3zq9drfxJbql9i82aiJrxCjQbRpa4c_JfhcVEdH1hRkRVoANNqv7mjI-D9r-y-bQTS5akeWIfy6c_OpzH1H87_Rddt Tahvonen R. elai: Effect ofseed dressing treatment ofstreptomyces griseoviridis... Trichoderma and Gliocladium fungi and Strep- tomyces bacteria, have been shown to prevent growth of root rot pathogens on agar and to sup- press disease severity in bioassays and field tri- als (Domsch and Gams 1968, Uoti 1976, Har- man and Taylor 1990). Root inhabiting fluores- cent Pseudomonas bacteria have demostrated great potential in the control of take-all (Bowen and Rovira 1976,Weller and Cook 1983,Ryder et al. 1990). Seed dressing with spores or mycelia of the antagonist has proved to be a reliable way of controlling a number of diseases (Mangenot and Diem 1979, Papavizas and Lewis 1980). The antagonist applied to seeds protects them from infection and may also colonize therhizosphere. The activity of the antagonist can be intensifed by differentadditives, e.g. nutrients (Harman and Taylor 1990). Streptomyces griseoviridis Anderson et al. has been successfully used for controlling seed- borne diseases of cruciferous plants (Tahvonen and Avikainen 1987) and numerous soil-borne diseases (Tahvonen 1982, 1988). Preliminary studies of Tahvonen and Avikainen (1990) indi- cated that the antagonist also has potential for controlling common root, Fusarium spp. and B. sorokiniana, of cereals. This study investigates the efficacy of S. griseoviridis seed dressing on barley and spring wheat against foot rot diseas- es in field conditions and its effect on spring wheat and barley yields. Material and methods Crop-rotation experiments The performance of the antagonist Streptomy- ces griseoviridis in the field was studied in two crop-rotation experiments, with rotations main- taining different levels of soil-borne inoculum of root-rot pathogens, Fusarium spp., Gaeuman- nomyces graminis and B. sorokiniana. The five year crop rotation experiment con- ducted at Helsinki (Viikki) in 1982-86 consist- ed of four crop sequence types containing 100%, 75%, 50% or 25% wheat (cv. Ruso) or barley (cv. Kustaa). Both barley and wheat were grown in monoculture (100%), which was interrupted every three years with fallow (75%), barley and wheat were exchanged every other year for oats, turnip rape and field bean (50%) and barley and wheat were grown in-four year rotation with oats, turnip rape and field bean (25%) (Hannukkala 1985).At Jokioinen, a four-year barley (cv. Pok- ko) and wheat (cv. Luja) monoculture together with barley and wheat grown in one, two and three consecutive years after grass ley maintained three, two and one years, respectively were in- cluded in the crop rotation experiment in 1985- 87. Both experiments consisted of two sub-tri- als, one with barley and the other with wheat as the test crop. The experimental design was a split-plot model with four replications. Crop se- quences were placed in the main plots and the seed treatments in subplots. Plot size at Helsin- ki was 8 m 2 and at Jokioinen 10 m 2. Seed dressing experiments The effect of S. griseoviridis on seed-borne root- rot diseases was studied in 1984-86. A set of field experiments using artificially infected seed was carried out at three locations, Jokioinen, Kotkaniemi and Mietoinen, in 1984-85.Two bar- ley seed lots (cv. Pokko) were inoculated by soaking in aquaceous suspension of two patho- gens, Fusarium culmorum and B. sorokiniana as described by Tahvonen and Avikainen (1990). Seed lots heavily contaminated with common root rot pathogens were screened in pot experi- ments in 1986 (Tahvonen and Avikainen 1990). Four seed lots of barley (cvs. Arra, Etu, Pokko and Potra) and three seed lots of wheat (cvs. Luja and Tapio) were selected for the field test. A split-plot experimental design with four repli- cations, where the main plots were infected seed lots and the sub-plots were seed dressings, was used in both sets of experiments. The plot size was 10 m 2. 420 AGRICULTURAL SCIENCE IN FINLAND Vol. 4: 419^27. Biocontrol agent and seed treatments The S. griseoviridis used as a biocontrol agent in all studies was originally isolated from Finn- ish peat (Tahvonen 1982). In 1982-84 the seed was treated with the spore suspension of the an- tagonist in sterile water as described by Tahvo- nen (1982). In 1985-87 the seed was treated with a powdery product, “Mycostop” Kemira Oy, Fin- land, containing mycelium and spores of S. gri- seoviridis at a minimum of 10s cfu per g (Tah- vonen and Avikainen 1987). Mycostop was applied to seeds by shaking them with the powdery product in the same man- ner as standard fungicides. The standard dose was 3 g Mycostop/kg seed. An additional dose of 10 g Mycostop/kg seed was included in the crop rotation experiment at Jokioinen and the experiment with naturally infested seed. An un- treated control was included in all experiments. Standard organomercury treatment (Täyssato, Kemira Oy or Ceresan, Berner Oy (metoxyethyl- mercurychloride a.i.) 2g/kg seed) was used in all experiments except the crop-rotation experiment at Helsinki. Other trial methods and analyses The soil type in all experiments was heavy clay with the exception of those at Kotkaniemi, where it was fine sand. Soil acidity ranged from pH 5.5 to 6.5. Trials received 80 kg N/ha in the form of compound fertilizer. The type of ferti- lizer chosen depended on the nutritional status of each individual experimental field. Commer- cial herbicides were used for weed control, de- pending on the dominant weed population in the field. Growing seasons during the study were ex- tremely variable. Sowing dates varied from the last week of April to the third week of May and harvesting dates from the fourth week of August to the third week of September. The beginning of the growing season in 1982 and 1985 was exceptionally cool and moist. In 1983, 1984and 1986 the spring was warm and, especially in 1984, very dry. The 1987 Growing season was one of the coldest this century . The stem bases of the plants were rated for disease at growth stage 20-30 (Zadoks et al. 1974) from a sample of 25-50 plants/plot. At Helsinki an additional sample was taken at growth stage 75 and both stem bases and roots were rated for the disease. The disease data were studied by the loglinear modelling available in the SAS CATMOD procedure. For modelling the original disease ratings were grouped into three symptom classes (healthy, moderate and severe). Disease ratings are not presented in the results, because there were no statistically significant differences between treatments. The yield data were analysed by modifica- tions of the analysis of variance according to each experimental design using the SAS GLM procedure. Before the analyses of variance the data were studied by the SAS UNIVARIATE procedure to confirm that the data fulfilled the assumptions of analysis of variance. No trans- formations were needed for the data. The data were further studiedby the Tukey HSD test. Sta- tistical significances are expressed by asterixes (*** , P < 0.001; **, P < 0.01; �, P < 0.05; NS, P > 0.05) and/or using different letters to show individual means belonging to the different group at the 0.05% significance level. Results and discussion Seed treatment with S. griseoviridis suspension increased yields considerably in the crop rota- tion experiment at Viikki in 1982.The maximum yield increase in barley was about 640kg/ha and in wheat 310 kg/ha. The high yield increases encouraged us to continue testing and to start new field studies. The following years however, showed that neither the suspension nor the pow- dery product of the antagonist could provide any consistent positive effect on yield. On average over years and crop sequences, the antagonist increased barley yilds slightly but caused minor losses to wheat yields (Table 1). 421 AGRICULTURAL SCIENCE IN FINLAND Tahvonen R. etal: Effect ofseed dressing treatmentofstreptomyces griseoviridis... Table 1. Effect of Streptomyces seed treatment on wheat and barley yields in a five year crop rotation experiment at Viikki in 1982-86. Yield increase/decrease kg/ha Mean yield Crop sequence 1982 1983 1984 1985 1986 mean of untreated control Wheat Monoculture 311 -146 58 -110 85 40 3650 75% wheat 117 -223 -130 -85 -56 -75 4108 50% wheat -88 -298 15 5 -146 -102 4155 25% wheat -383 -110 -70 9 -13 -113 4017 Mean yield of 4831 5021 5066 2417 2949 untreated seed Barley Monoculture 289 37 174 -61 -264 35 4358 75% barley 638 -102 83 -64 -219 68 4384 50% barley 328 234 II 124 12 142 4435 25% barley 481 -180 -6 -174 -92 6 4745 Mean yield of 4889 5703 5145 3397 3090 untreated seed F-values: Wheat Barley Crop sequence (Cs) 14.73*** 16.41*** Year (Y) 1354.61*** 848.25*** Treatment (T) 10.97** 10.24** Y x Cs 10.58** 6.17** YxT 1.66 NS 7.21** Cs x T 1.12 NS 1.85 NS In the crop rotation experiment at Jokioinen, none of the seed treatments had a statistically significant effect on barley yields. Ley as the precrop decreased yields in 1986 and 1987 (Table 2). There were however, no statistically significant differences in visible stem base symp- toms between seed treatments or between crop sequences. In wheat all seed treatments increased yields as compared with the untreated control. Mercu- ry treatment always gave higher yield increases than Streptomyces-trcatment. Ley as a precrop decreased wheat yields each experimental year. The highest yield increases due to seed treat- ments were obtained after ley as the precrop (Table 3). No statistically significant differences in visible stem base symptoms were detected between seed treatments or crop sequences. The yield decrease after ley was probably caused by a biotic factor, which could be con- trolled to some extent by seed treatments. Ley probably increased the inoculum of some ’mi- nor’ pathogens (Salt 1979) e.g. snow mould, Microdochium nivale (Ces. ex Berl. & Vogl.) Samuels & Hallet, an agent that typically kills grasses in winter, may cause mild symptoms in both barley and wheat (Wiese 1987). The variations in the effects of seed treat- ments between years and experiments indicate that establishment of the antagonist is higly de- pendent on environmental factors, e.g. soil mois- ture and temperature, as was also stressed by Bowen and Rovira (1976), Papavizas and Lewis (1980) and Harman and Taylor (1990). The yield increases obtained with seed treatment despite insignificant differences in disease ratings may 422 AGRICULTURAL SCIENCE IN FINLAND AGRICULTURAL SCIENCE IN FINLAND Vol. 4: 419-427. Table 2. Effect of Sireptomyces and mercury seed treatment on barley yields in a four year crop rotation experiment at Jokioinen in 1985-87. Increase/decrease kg/ha Year Precrop Untreated Streptomyces Mercury control 3 g/kg 10 g/kg Mean kg/ha kg/ha F value 1985 ley 4427 35 19 256 4505 A precrop 2.53 barley 4643 67 39 19 4674 A seed tr. 0.69 mean 4535 a 51a 29 a 138 a 4589 A prec. x seed. 0.80 1986 ley + ley 3430 40 63 50 3468 A precrop 9.36* barley + ley 3177 126 126 313 3318 A seed tr. 1.27 barley + barley 3958 129 56 186 4051 B prec. x seed. 0.27 mean 3522 a 98 a 82 a 183 a 3612 1987 ley + ley + ley 3048 244 -168 174 3111 AB precrop 3.92* barley + ley + ley 3306 -521 -50 -293 3091 AB seed tr. 0.18 barley + barley + ley 2398 238 -78 248 2500 A prec. x seed. 1.92 barley + barley + barley 3266 100 163 30 3340 B mean 3005 a 15 a -33 a 40 a 3010 Table 3. Effect of Sireptomyces seed and mercury treatment on spring wheat yield in a four-year crop rotation experiment at Jokioinen in 1985-87. Increase/decrease kg/ha Year Precrop Untreated Streptomyces Mercury control 3 g/kg 10 g/kg Mean kg/ha yield kg/ha F value 1985 ley 3466 528 342 860 3899 A precrop 17.26** wheat 3986 433 437 632 4362 B seed tr. 30.99 *** mean 3726 a 480 b 390 b 746 c prec. x seed. 1.54 1986 ley + ley 2714 80 219 423 2894 A precrop 14.82*** wheat + ley 2682 66 149 439 2845 A seed tr. 18.97*** wheat + wheat 3150 35 -4 352 3245 B prec. x seed. 0,50 mean 2848 a 61a 121 a 405 b 2995 1987 ley + ley + ley 1670 416 475 546 2029 A precrop 14.36*** wheat + ley + ley 2365 119 50 -39 2398 AB seed tr. 0.70 wheat + wheat + ley 2503 106 -115 171 2543 B prec. x seed. 1.71 wheat + wheat + wheat 3218 -163 -1 -278 3108 C mean 2439 a 119 a 102 a 100 a 2519 423 Tahvonen R. etal: Effect ofseed dressing treatment ofstreptomyces griseoviridis... Table 4. Effect ofStreptomyces and mercury treatment of uninoculated seeds(l) or of barley seeds inoculat- ed with Fusarium culmorum (II) or Bipolaris sorokiniana (III) on yield at three different experimental places. Yield and yield increase/decrease kg/ha Location Seed treatment I II II Mean 1984 Jokioinen Untreated 5611 5689 5639 5646 Streptomyces -192 -213 -159 -188 Mercury -17 -17 -106 -50 Kotkaniemi Untreated 2528 2378 2911 2606 Streptomyces +230 +314 +l9B +247 Mercury +234 +295 +3l +lB7 Mietoinen Untreated 4660 4710 4710 4693 Streptomyces -120 +l3O +lO +7 Mercury +9O +3O +l3O +B3 1985 Jokioinen Untreated 6232 6519 6209 6320 Streptomyces -52 -310 +3Ol -20 Mercury +95 +195 +606 +299 Kotkaniemi Untreated 6492 6193 6100 6262 Streptomyces -383 +177 -33 -80 Mercury +3 +lB5 +422 203 Mietoinen Untreated 4560 4330 4460 4450 Streptomyces -100 +2OO +l4O +BO Mercury +l5O +230 +l6O +lBO Mean Untreated 5013 4970 5005 4996 Streptomyces -71 +3 +145 +25 Mercury +93 +153 +207 +l5l F values: No significant differences between treatments be due to the ability of the antagonist to stimu- late plant growth. Numerous soil and rhizosphere bacteria are known to stimulate crop growth (Gerhardson et al. 1985). Certain Actinomycetes belonging to the genus Streptomyces have been reported to promote wheat growth (El-Shan- shoury 1989). In experiments with artifically infested seed, inoculation withF. culmorum or B. sorokiniana caused little increase in disease incidence or de- crease in yields as had been the case in prelimi- nary pot experiments (Tahvonen and Avikainen 1990). Seed dressings with mercury or Strepto- myces had no statistically significant effects on yields, though both treatments caused slight yield increases on average in all experiments (Table 4). In 1986, when naturally infested seed was used in the experiments, treatment with My- costop increased wheat yields by 130 kg/ha and with the organomercurial compound by 580 kg/ ha. Seed treatments had no statistically signifi- cant effects on barley yields (Table 5). Fusari- um is known to be more destructive to wheat than barley, and healthy barley plants in the stand have a high capacity to compensate for the negative effects of diseased plants by more vigorous growth (Wiese 1987). These results indicate that seed treatment witheither fungicide or biopesti- cide is more important in wheat than in barley for the control of common rot caused by Fusar- ium spp. The studies of Kurppa (1985) have shown that fungicides can significantly reduce 424 AGRICULTURAL SCIENCE IN FINLAND Vol. 4: 419-427. Table 5. Effect of seed treatment with Streptomyces and mercury on yield of four barley seed lots and six wheat seed lots in 1986 at Jokioinen. Treatment Wheat Barley Yield kg/ha Range Yield kg/ha Range Untreated 4177 a 3705 - 4446 4347 a 2903-5291 Mycostop 3g/kg +l34b +l2-+267 +lO a -355-+234 Mycostop lOg/kg +129 b +32-+224 +47 a -116-+193 Mercury +577 c +383-+925 -44 a -247-+149 Different letters show individual means belonging to the different group at the 0.05 % significance level. seed surface infection by B. sorokiniana but that they do not provide reliable control when seed is heavily infested. Some antagonists have potential in the bio- logical control of root rots of cereals. S. griseo- viridis was originally isolated from peat, and the biopreparate Mycostop was developed to con- trol diseases of greenhouse crops grown in a controlled environment (Tahvonen and Avikai- nen 1987, Lahdenperä 1987, 1992). S. griseo- viridis has shown potential to control eyespot disease ofcereals (Clarkson and Lucas 1993) and ear blight of wheat caused by Fusarium spp. (Lahdenperä et al. 1992). To control truly soil- borne diseases in heavy clay soils in a cool cli- mate it is essential to look for microbes adapted to the soil environment where they will actually be used. In conclusion, wheat yields can be increased by seed dressings more efficiently than can bar- ley yields. Both fungicides and biopesticides can also affect soil-borne infection when the infec- tion pressure is low. The S. griseoviridis prepa- rate gave some protection against common root rot and was able to increase yields. However, chemical control with an organomercurial com- pound resulted in yield increases two to three times higher than those with the biopreparate tested. References Bowen, G. D. & Rovlra, A. D. 1976. Microbial coloniza- tion of plant roots. Annual Review of Phytopathology 14: 121-144. Clarkson, J. P. & Lucas, J. A. 1993. Screening for po- tential antagonists of Pseudocercosporella herpotri- choides, the causal agent of eyespot disease of cereals 1. Bacteria. Plant Pathology 42: 543-551. Domsch, K. H. & Gams, W. 1968. Die Bedeutung vor- fruchtabhängigerVerschiebungen in der Bodenmikroflo- ra. I. Der Einfluss von Bodenpilzen zum Wurzelentwick- lung von Weizen, Erbsen und Raps. Phytopathologische Zeitschrift 63: 64-74. El-Shanshoury, A. R. 1989. Growth promotion of wheat seedlings by Streptomyces atroolivaceus. Journal of Agronomy and Crop Science 163: 109-114. Gerhardson, 8., Alström, S. & Rämert, B. 1985. Plant reactions to inoculation of roots with fungi and bacteria. Phytopathologische Zeitschrift 114: 108-117. Hannukkala, A. 1985. Inverkan av ensidig spannmålsod- ling på stråbassjukdomar. Växtskyddsnotiser 49: 75-78. - 1988. Vehnän ja ohran tyvi- ja juuristotaudit eri viljelyjärjestelmissä. Licentiate dissertation. 94 p. Helsin- ki. Harman, G. E. & Taylor, A. G. 1990. Development of an effective biological seed treatment system. In: Hornby, D. (ed.). Biological control of soil-borne plant pathogens. Wallingford, Oxon. C. A. B. International, p. 415-426. Kurppa, A. 1985. The pathogenicity and importance of seed-borne infection by Bipolaris sorokiniana on barley in Finland. Journal of Agricultural Science in Finland 57: 107-115. Lahdenperä, M-L. 1987. The control of Fusarium wilt on carnation with Streptomyces preparation. Acta Horticul- ture 216: 85-92. - 1992. Biological control of Gerbera wilt on rockwool. Bulletin OILB/SROP 15, 1: 124-126. -, Simon, E. & Uoti, J. 1992. Mycostop - a novel biofun- gicide based on Streptomyces bacteria. Proceedings of 425 AGRICULTURAL SCIENCE IN FINLAND Tahvonen R. etai: Effect ofseeddressing treatment ofstreptomyces griseoviridis... the First Conference of the EuropeanFoundation for Plant Pathology. Developments in Agricultural and Managet- Forest Ecology 23: 258-263. Mäkelä, K. & Parikka, P. 1980. Root and foot rot diseas- es of cereals in Southern Finland in 1975-78. Annales Agriculturae Fenniae 19: 223-253. Mangenot, F. & Diem, H. G. 1979. Fundamantals of bio- logical control. In: Krupa, S. V. & Dommerques, Y. R. (eds.). Ecology of root pathogens. Amsterdam, Oxford, NewYork, Elsevier Scientific Publishing Company, p. 207- 265. Papavizas, G. C. & Lewis, J. A. 1980. Introduction and augmentation of microbial antagonists for the control of soilborne pathogens. Beltsville Symposia in Agricultural Research (5). Biological control in crop production. Lon- don. p. 305-322. Ryder, M. H., Brisbane, P. G. & Rovira, A. D. 1990. Mechanisms in the biological control of take-all of wheat by rhizosphere bacteria. In: Hornby, D. (ed.). Biological control of soil-borne plant pathogens, Wallingfort, Oxon. C. A. B. International, p. 123-130. Salt, G. A. 1979. The increasing interest in minor patho- gens. In: Shippers, B. & Gams, W. (eds.). Soil-borne plant pathogens, London, New York, San Francisco, Academic Press, p. 289-312. Tahvonen, R. 1982. Preliminary experiments into the use of Streptomyces spp. isolated from peat in the biological control of soil and seed-borne diseases in peat culture. Journal of the Scientific Agricultural Society of Finland 54: 357-369. - 1988. Microbial control of plant diseases with Strepto- myces spp. EPPO Bulletin 18: 55-59. - & Avikainen, H. 1987, The biological control of seed- borne Alternaria brassicicola of cruciferous plants with a powdery preparation of Streptomyces sp. Journal of Ag- ricultural Science in Finland 59: 199-208. - & Avikainen, H. 1990, Effect of Streptomyces sp, on seed-borne foot rot diseases of wheat and barley. I. Pot experiments. Annales Agriculturae Fenniae 29:187-194. Uoti, J. 1976. The effect of five Fusarium species on the growth and developement of spring wheat and barley. Annales Agriculturae Fenniae 15: 254-262. - 1979. Study of control of seed-borne Fusarium in cere- als. Annales Agriculturae Fenniae 18: 149-153. Weller, D. M. & Cook, R. J.1983. Suppression of take- all of wheat by seed treatments with fluorescent Pseu- domonas. Phytopathology 73: 436-469. Wiese, M. V. 1987, Compendium of wheat diseases. 2nd ed, St, Paul, Minnesota, American Phytopathological Society. 112 p. Yarham, D. J. 1981. Practical aspects of epidemiology and control. In: Asher, M. J. C. & Shipton, P. J. (eds.). Biology and control of take-all. London, New York, Toron- to, Sydney and San Francisco, Academic Press, p. 353- 384. Zadoks, J. C., Chang, T. T. & Konzak, C. F. 1974. A decimal code for the growth stages of cereals. Weed Research 14: 415-421. 426 AGRICULTURAL S C II N CE IN FINLAND Vol. 4: 419-427. SELOSTUS Streptomyces griseoviridis siemenpeittauksen vaikutus ohraan ja kevätvehnään kenttäkokeissa Risto Tahvonen, Asko Hannukkala ja Hanna Avikainen Maatalouden tutkimuskeskus Streptomyces griseoviridis -sädesientä ja siitä tehtyä jauhemaista Mycostop-valmistetta testattiin vehnän ja ohran siemen-ja maalevintäisten tautien torjumisek- si, Siemenet kasteltiin mikrobin itiösuspensiolla tai ravistettiin mikrobijauheen kanssa peittauslaitteessa. Peittauksen tehoa selvitettiin luontaisesti ja keinote- koisesti saastutetuilla siemenillä ja erilaisissa esikas- vikokeissa. Monipuolisessa kiertoviljelykokeessa oli esikasveina eri pituisia aikoja kaura, rypsi ja härkä- papu . Toisessa esikasvikokeessa oli esikasvina nur- mi eri pituisia aikoja. Kokeet tehtiin vuosina 1982- 1987Viikissä, Kotkaniemessä, Mieleisissä ja Jokioi- silla. Monipuolisessa vuoroviljelykokeessa Strepto- myces-peittaus lisäsi ohrasatoja, mutta vehnällä ei keskimäärin saatu sadonlisäyksiä. Vuosien väliset vaihtelut olivat suuria. Vuoroviljelykasvit lisäsivät vehnän satoa, mutta ohralla yksipuolinen viljely ei sanottavasti alentanut satoa suhteessa vuoroviljelyyn. Nurmi ohran ja vehnän esikasvina alensi satoja, voi- makkaammin vehnällä kuin ohralla. Siemenen peit- taus lisäsi satoja varsinkin vehnällä, kun esikasvina oli ollut nurmi. Kemiallinen elohopeapeittausaine antoi suuremman sadonlisän kuin Streptomyces-peit- taus. Parhaimmat sadonlisät olivat 860 kg/ha. Siemenlevintäiset Fusarium- ja Bipolaris- sienet eivät vaikuttaneet ohran satoihin, jolloin peittauksil- lakaan ei saatu sadonlisiä. Vehnällä siemenen peittaus lisäsi satoja, kun siemen oli luontaisesti Fusarium- sienten saastuttamaa. Kemiallinen elohopeapeittaus antoi paremman tuloksen kuin biologinen peittaus. Tehdyt kokeet osoittivat, että biologisella Strep- romyces-peittauksella voidaan saada sadonlisäyksiä, mutta kemiallisella peittauksella tulos on pelto-olois- sa aina parempi. Tämän takia pelto-oloja varten tar- vitaankin tehokkaampia antagonisteja, jos viljan vil- jelyssä halutaan käyttää biologista torjuntaa. 427 AGRICULTURAL SCIENCE IN FINLAND