Maataloustieteellinen A ikakauskirja Vol. 57: 107—115, 1985 The pathogenicity and importance of seed-borne infection by Bipolaris sorokiniana on barley in Finland AARNE KURPPA Department of Plant Pathology, University of Helsinki* SF-00710 HELSINKI 71 Finland Abstract. Seed-borne infection by Bipolaris sorokiniana decreased the percentage germi- nation of barley seeds and the emergence of seedlings. Infection levels were higher in non- germinated than in germinated seeds. Seed treatment with organomercurial fungicide or imazalil improved the percentage emergence but a low number of diseased seedlings still re- mained in the crops. The fungus caused a reduction in grain yields in most experiments and also decreased their value as sowing seed, if the weather conditions were favourable for com- pute disease expression. Yield losses in greenhouse experiments varied from 7.2 to 38.5 % and in the field from sto 11 %, and showed a strong correlation with the infection levels in the seed stocks. Higher losses were associated with the six-row cultivars. Organomercury seed treatment resulted in a slight but insignificant increase in yields but it was able to prevent an occurrence of secondary infection in the crop resulting in a lower seed infection levels of the grain. In field experiments in Inari (69° N.L.) seed-borne inoculum could be demonstrated clearly to be the only source of a severe disease outbreak. The inoculum remaining in the soil was capable of initiating soil-borne infection of barley seedlings during the following two growing seasons. Introduction Bipolaris sorokiniana (Sacc. ex Sorok.) Shoem. (syn. Helminthosporium sativum Pamm., King & Bakke), perfect state Coch- liobolus sativus (Ito & Kurib.) Dastur has been recently reported to be increasingly common in commercial barley seed stocks in � Present address: Agricultural Research Centre Department of Plant Pathology SF-31600 JOKIOINEN, Finland North Western Europe (de Tempe 1964, Jor- gensen 1974, Hewett 1975, Olofsson 1976, Kurppa 1984). Estimates concerning its ec- onomic importance have been variable but the latest information assumes losses in yield of up to 15 % due to a high level of seed in- fection (Whittle & Richardson 1978). Dis- eased plants from infected seeds have also been found serving as important sources for spore liberation during later developmental stages of the crop, and their residues remain Index words: Bipolaris sorokiniana, Helminthosporium sativum, Cochliobolus salivus, common root rot, kernel blight 107 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=ifkk39v0R7EF-ae6.CN5SmF15JVGmh95Hk6q97A.ZXqPuFdoCcsXkM0v3Dt_cX8PS5X9qGU27YvLsM1bou1dkx3PhKXHn5_83NbH2IfV9pKgxptoVwKd0gFeYyk2oXguiqHF0sHYXg8JQ1J7BZYchmaHTVA2gJinFP1_f87Sor8r5pfQfpWwL-svt5PtoW8-fCXmlhiDSoA 108 objects for further sporulation (Chinn 1977, Reis & Wunsche 1984). The persistence of B. sorokiniana in barley seed for 10 years or more precludes ageing as practical method for obtaining seeds free from the pathogen (Machacek & Wallace 1952, Couture & Sutton 1980). Seed treat- ment with organomercurial or systemic fun- gicides (Hewett 1975, Chinn 1978, Whittle & Richardson 1978) has resulted in satisfac- tory control of the disease. Materials and Methods Determination of percentage germination in seed stocks including examination for fun- gal growth was carried out in petri dishes as described by Kurppa (1984). Percentage emergence was determined by the official method used at State Seed Testing Institute, Helsinki. Field experiments at Viikki, Hel- sinki and Muddusniemi Research Station, Inari, and pot experiments at Viikki were de- signed to study disease development, varietal differences and the effects of seed-borne dis- ease and seed treatment on grain yield and infection levels. Seed stocks used for sowing in the experiments originated from a field ex- periment at Viikki (Kurppa 1985 b.), or were selected from commercial stocks exam- ined at State Seed Testing Institute. This ma- terial included stocks with various levels (19—92 %) of seed and embryo infection, and was classified according to the latter pa- rameter. Class a indicates low, b moderate and c high infection levels. In greenhouse experiments barley was grown in plastic 25 x 25 cm pots filled with non-sterilized loamy field soil, which was previously determined to be free of the path- ogen. In field experiments a plot size of 5 x 1.33 m was used. Experimental soils were fertilized with a commercial N-P-K (15-20-15) fertilizer, 500 kg/ha in field experiments or 3 g/pot in greenhouse experiments. For seed treatment an organomercuric fungicide (Ce- resan 2 g/kg seeds), benomyl (Benlate 1 g/kg and imazalil (experimental sample 0.3 g a.i./kg) were used. In the field barley was sown in a density of 400 (six-row cvs) or 450 (two-row cvs) seedlings/m 2 and in green- house experiments 50 seeds were sown/pot. The pots were watered as required with an equal volume per pot of tap water. The seedling population was counted at the 3—4 leaf stage and samples (25 seed- lings/plot) were collected in the field. The second sampling occurred close to the yellow ripening stage. Basal stems of the plants showing disease symptoms were surface-ster- ilized with Na-hypochloride and plated on potato dextrose agar (PDA). After 7 days of incubation at room temperature the samples were examined for the presence of B. soroki- niana. Pots and field plots were harvested when ripe, grain yields were drained immedi- ately, weighed, and samples were taken for grain analysis. Analysis of variance and linear regression equations with correlation coefficients was used to test the signicance of the results. The weather conditions at Viikki during research period were as follows: The growing seasons of 1973 and 1975 were warm and dry, the season of 1979 was near average and the rest were cooler than average with high rainfall (Anon 1973—1979). Results B. sorokiniana significantly decreased per- centage germination in all stocks of seed in- fected at various levels (Table 1). Non- germinated seeds carried higher levels of in- fection in all seed classes of all barley culti- vars tested. Reduction in percentage germi- nation was particularly related to embryo in- fection by the fungus (Fig. 1). The fungus had a stronger effect on field emergence than on laboratory germination of the seeds (Ta- ble 2). A high number of young infected seedlings failed to emerge and those capable doing so showed seedling blight symptoms (Fig. 5). The mean percentages of reduction in emergence of seedlings in 14 pot experi- ments and 18 field experiments were record- Table 1. Germination of barley seed stocks infected at various levels by Bipolaris sorokiniana and infection levels in germinated and non-germinated seeds. Seed Cultivar Ingrid Karri Otra Porno Mean GER MI G NG* GER MI G NG GER MI G NG GER MI G NG GER MI G NG a 190.8 9.3 8.0 21.2 89.5 14.0 10.0 32.2 96.0 10.0 9.1 31.3 90.5 9.5 7.4 23.5 91.3 10.7 8.7 27.0 b 86.8 57.7 55.7 73.2 82.8 83.5 81.8 88.1 95.8 52.3 47.5 53.3 89.3 58.7 57.9 67.8 88.7 63.8 61.2 70.3 c 89.3 63.2 62.2 70.9 83.0 84.3 83.2 91.1 94.8 78.3 77.5 87.5 90.3 66.7 65.8 76.3 89.3 73.1 72.1 81.5 Mean 88.9 43.3 42.6 55.1 85.1 60.3 58.3 70.5 95.5 46.9 44.7 57.0 90.0 45.0 43.7 55.8 47.3 59.6 * GER = Per cent germination of seed stocks F-value: Germination in seed stocks = 11.4**, LSD 1005 = 2.15 % MI = Mean infection (per cent) Differences in fungal incidences in germinated and non-germinated seeds werenot tested G = Infection level in germinated stocks (per cent) statistically because without exception non-germinated seeds carried higher fungal NG = Infection level in non-germinated stocks (per cent) incidences. 1 For seed classes see text ed. In pot experiments, an improvement in emergence of 7 per cent was recorded with organomercury seed treatment, while benomyl and imazalil caused improvements of 3 and 5 per cent respectively. In the field improve- ments of 16 and 5 per cent were reached with organomercury and imazalil treatments but benomyl had no positive effect (Table 2). Seedlings from seeds with embryo infection frequently showed disease symptoms in spite Fig. I. The effect of fungal invasion on germination of seed stocks of four barley cultivars. Correla- tion coefficients: Ingrid, r = —0.58" Karri, r= 0.62\ Otra, r = —0.80", Porno, r = —0.48. Fig. 2. The effects of seed infection by Bipolaris soro- kiniana and seed treatment on the grain yield of two barley cultivars in greenhouse experi- ments. Infection levels in sowing seed were 60 % (cv. Vigdis) and 92 °/o (cv. Pa;.vo). 0 indicates untreated seed, B and M were treated with benomyl and organomercury respectively. F- values: Seed infection = 86.1", LSD 00! = 10.7 %, Seed treatment < 1. 109 Table 2. Emergence of barley seed infected with Bipolaris sorokiniana, with and without seed treatment. Treatment Emergence Greenhouse experiments Field experiments Healthy untreated seed 94.5* (7)' 55.32 (4) Untreated infected seed' 80.5 (7) 45.1 (4) Organomercury treated infected seed 86.4 (7) 52.2 (4) Benomyl treated —» 82.7 (4) 44.9 (2) Imazalil treated —» 84.7 (2) 47.3 (2) * Per cent emergence 1 Number of experiments : Number of seedlings/drill m 3 Infection levels from 19 to 92 °7o In all individual experiments analyzed statistically, organomercury seed treatment of infected seed significantly in- creased germination and emergence at P = 0.05 level. Table 3. The effects of seed infection levels of Bipolaris sorokiniana and of seed treatment on grain yields of four barley cultivars in greenhouse experiments. Seed Cultivar Ingrid Karri Otra Pomo Means 0 1 1 0 1 0 1 0 1 0 10+1 h: 100.0* 103.7 100.0 104.0 100.0 89.5 100.0 98.5 100.0 99.0 99.5 b 102.2 94.7 84.2 83.7 90.5 96.5 79.2 78.7 89.0 88.4 88.7 c 94.5 91.2 93.2 90.5 85.7 76.7 78.0 66.7 87.8 81.3 84.6 Mean 98.9 96.6 92.5 92.8 92.1 87.6 85.7 81.3 92.2 89.6 1 0 ■ Untreated seed F-values: Infection levels = 71.3", LSD,OoS = 2.8 % 1 = Organomercury treated seed Cultivars = 10.8", = 9.0 % 2 h = Healthy seed Seed treatment < 1 b = Embryo infection levels from 4to 10 % c = » 22 to 36 % * Relative grain yield; controls for each cultivar = 100.0 Fig. 3. The effects of seed infection level and seed treatment with organomercury powder on grain yields of barley cultivar Paavo in green- house experiments. F-values: Seed infection level = 50.9", LSD005 = 0.44 g, Seed treat- ment < 1. Fig. 4. The effect of plant density on grain yields of barley cvs. Birgitta and Otra. For sowing, pathogen-free seed was used. F-value = 1.8, not significant. 110 Table 4. The effects of seed infection and seed treatment on yield and infection incidence in grain on barley cv. Vigdis in a field experiment. Seed treatment Grain yield kg/plot % incidence of B. sorokiniana Sowing seed Sowing seed Healthy Infected* Mean Healthy Infected Mean None 3.415 3.090 3.252 3.3 17.5 10.4 Benomyl 3.225 3.082 3.153 8.3 22.5 15.4 Organomercury 3JOO 3J>O7 3jto3 7J 5/7_ Mean 3.313 3.226 5.2 15.8 Seed infection level = 60.0 % F-values: Sowing seed/yield = 4.7» , LSDtOO5 = 0.316 kg —» /infection incidence in grain = 34.2XX , = 5.8 % Seed treatment/ —» — = 7.4 XX , =7.7 % Table 5. Pathogenicity of seed-borne infection of Bipolaris sorokiniana on five barley cultivars in field experi- ments and the effect of seed treatment to control the disease. Seed Cultivar treatment 7 ~ Z ~ '. ~ I 7~, ~ Otra Vigdis Karri Pomo Ingrid Mean H 1 I HI HI HI HI H I H + I None 100.0* 93.5 100.0 89.0 100.0 95.0 100.0 95.0 100.0 96.5 100.0 93.7 96.9 Organo- mercury 96.2 93.2 98.4 93.4 102.5 97.9 101.8 95.1 101.5 96.9 100.0 95.4 97.7 Mean 98.1 93.4 99.2 91.2 101.3 96.5 100.9 95.0 100.7 96.7 100.0 94.5 Imazalil 94.9 92.3 95.9 90.6 95.1 94.0 Mean 97.0 93.0 98.1 91.0 99.2 95.6 1 H = Healthy seed; I = Seed infected at levels from 60 to 84 % * Relative mean grain yield of three experiments; controls for each cultivar = 100.0 F-values: Seed infection/grain yield (all cultivars) = 31.4", LSD, OO! = 4.9 % Organomercury seed treatment of infected seed (all cultivars) = 1.3 Organomercury or Imazalil treatment (cvs Karri, Otra and Vigdis) < 1 of previous seed treatment and their further development typically resulted in root rot with low grain yield (Fig. 6). The diseases on barley originating from seed-borne infection by B. sorokiniana re- sulted in significant losses in grain yield in most experiments and also in a decrease in its value as sowing seed, if the weather condi- tions were favourable for complete disease expression. A mean yield reduction of 38.5 % was reached in one series of pot experiments (Fig. 2) but in another (Table 3) it was lower with the following means for the cultivars: Ingrid 7.2, Karri 8.1, Otra 18.8 and Porno 27.6 Vo. Table 6. The effects of seed infection and seed treat- ment on estimated grain yield and its infec- tion incidence in barley cv. Vigdis in a field experiment in Inari (69° N.L.). Seed Grain Incidence of yield B. sorokiniana in grains IP El Healthy untreated 227.8* 25.5 4.5 Infected » 2 224.2 32.7 10.5 » benomyl treated 223.6 36.0 11.5 » organomercury treated 223.0 32.3 9.5 II = Infection incidence in the grains (%) El = Embryo infection » Grain yield g/200 heads 2 Infection level in the seed = 60 % 111 An experiment with seed stocks of cv. Paavo containing .various infection levels presented a significant correlation between infection level and grain yield (Fig. 3). Or- ganomercury or benomyl seed treatment had a minor effect on yield improvement in pot experiments (Table 3, Figs 2 and 3), although a delay in disease expression was observed. A variation in population from 25 to 50 seed- lings per pot in the healthy crop had no sig- nificant effect on yield (Fig. 4). Seed-borne infection by the fungus resulted in a relatively low but in most cases signifi- cant reduction in yields in field experiments. A 60 % level of seed infection caused a mean reduction in yield of 9 % on barley cv. Vigdis without seed treatment (Table 4). Organo- mercury seed treatment, however, signifi- cantly improved the yield but benomyl failed to do so. Infection levels in grain yields from the plots sown with infected untreated or benomyl treated seed were significantly higher than from the rest of the plots. Field experiments with five barley culti- vars over three years resulted in a mean reduction of 6.3 % (ranging from s—ll5 —11 %) in the yields from the plots sown with mod- erately or highly infected seed without seed treatment (Table 5). Organomercury seed treatment increased the yield somewhat but the treatment remained insignificant. Sec- ondary infection frequency in the crops dur- ing the experimental years (1975 —1977) re- mained low and no outstanding foliar dis- ease or grain infection occurred. The effect of seed-borne infection on the foliar disease outbreak could be clearly dem- onstrated with field experiments in Inari, Lapland, where the fungus was naturally absent. The fungus, which initiated from pri- marily diseased seedlings, sporulated inten- sively and caused an epidemic in the experi- mental crops, resulting also in high inci- dences in infection in the grain (Table 6). A high level of fungal inoculum remained in the soils with the crop residues and was ca- Fig. 5. Seedling blight and pre-emergence blight orig- inating from seed-borne infection in field ex- periments. Fig. 6. Fungal growth originating from infected organo mercury treated seed. 112 pable of infecting barley seedlings in the fol- lowing two growing seasons. Discussion The seed-borne inoculum of Bipolaris so- rokiniana is unquestionably of great impor- tance in initiating root rot and foliar diseases on barley grown in cool and temperate re- gions with relatively high rain fall during growing seasons. This significance is sup- ported by the lifecycle of the fungus as well as by the high incidences of seed infection on barley reported by de Tempe (1964), Jorgen- sen (1974), Whittle (1977) and Kurppa (1984). There is a lack of agreement on the effect of the fungus on seed germination. Reports published by de Tempe (1964) and Hewett (1975) deny its importance but a number of studies including the present support it. A study by Clark and Wallen (1969) reports a reduction in germination of as high as 38 %. Comparable data on the reduction in emer- gence has been reported by Olofsson (1976). In the present study, yield losses in field experiments due to the fungus were sim- ilar to those reported by Whittle and Ric- hardson (1978), but the increase in the yield as a result of seed treatment remained lower. A high incidence of fungus located deebly embedded in the grain embryos probably decreased the effectiveness of control ob- tained with seed treatment. Due to this fac- tor a sufficient number of diseased plants existed in the crop able to initiate secondary infection of the fungus when weather condi- tions were favourable. Among the fungicides used for seed treat- ment the organomercurial compound was fairly effective eradicating the fungus from superficially infected seeds but was not ca- pable of controlling disease initiating from internally infected seeds. Severe outbreaks of the disease in barley originating from or- ganomercury treated seed as reported by Whittle (1977) could probably be explained by this phenomen. The yields from the plots sown with imazalil treated seeds remained lower than those from organomercury treated seeds although this fungicide was highly ef- fective on the fungus as also reported by Chinn (1978). Possibly the dose of 0.3 g a.i./kg seeds was too high, causing toxic ef- fects on young barley seedlings. A number of systemic fungicides effective against B. sorokiniana have been shown to be phyto- toxic to barley by Couture and Sutton (1978). The ineffectiveness of benomyl treat- ment against the fungus agrees with the observations of Richardson (1972). The differences in yield losses between cul- tivars remained less significant than expected, regarding the earlier information by Kurppa (1985 a., b.) on varietal susceptibility to soil- borne and secondary infection. The differ- ences were, however, comparable to those in the previous studies. The lack of outstanding varietal differences is probably due to the high levels of infection in the seed stocks of all cultivars tested. However, a few specific cultivars have always been associated with a high seed infection level. Seed-borne infection of B. sorokiniana in barley was clearly demonstrated to be an im- portant or even the only way for the fungus to initiate the disease in remote areas. The present study reports for the first time the ability of B. sorokiniana to overwinter in soil and then to induce disease in barley north of the Artie Circle. Acknowledgements. The State Seed Testing Institute is acknowledged for providing research material. I also wish to thank Ms. Jennifer Shier for linguistic revision of the English text. 113 References Anon. 1973—1979. Kuukausikatsauksia Suomen sää- oloihin. Ilmatieteen laitos, Helsinki. Chinn, S.FLF. 1977. Influence of fungicide sprays on sporulation of Cochliobolus salivas on Cypres wheat and on conidial populations in soil. Phytopath. 67: 133—138. —, 1978. Influence of seed treatment with imazalil on common root rot and the size of the subcrown inter- node of wheat. Phytopath. 68: 1662—1666. Clark, R.V. & Wallen, V.R. 1969. Seed infection of barley by Cochliobolus salivas and its influence on yield. Can. PI. Dis. Surv. 49: 60—64. Couture, L. & Sutton, J.C. 1978. Efficaties of fungi- cides in cotrolling spot blotch of barley. Can. J. PI. Sci. 58: 311—317. —, 1980. Effect of dry heat treatments on survival of seed borne Bipolaris sorokiniana and germination of barley seed. Can. PI. Dis. Surv. 60: 59—61. Hewett, P.D. 1975. A health survey of seed barley. PI. Path. 24: 229—232. Jorgensen, J. 1974. Occurence and importance of seed borne inoculum of Cochliobolus salivas on barley in Denmark. Acta Agric. Scand. 24: 49—54. Kurppa, A. 1984. Bipolaris sorokiniana on barley seed in Finland, J. Agric. Sci. Finl. 56: 175—181. —, 1985 a. Reaction of spring barley cultivars grown in Finland to soil-borne infection by Bipolaris sorokinia- na and to its toxic metabolites. J. Agric. Sci Finl. 57: 85—96. —, 1985 b. The response of some spring barley cultivars grown in Finland to air-borne secondary infection by Bipolaris sorokiniana. J. Agric. Sci. Finl. 57: 97—105. Machacek, J.F. & Wallace, H.A.H. 1952. Longevity of some common fungi in cereal seed. Can. J. Bot. 30: 164—169. Olofsson, B. 1976. Undersökningar rörande Drechslera-arter hos korn och havre. Meddn St. VäxtskAnst. 16 (nr 172): 323—425. Reis, E.R. & Wunsche, W.A. 1984. Sporulation of Cochliobolus salivas on residues of winter crops and its relationship to increase of inoculum density in soil. PI. Dis. 68: 411—412. Richardson, L.T. 1972. Effectiveness of systemic fun- gicides seed dressing as protectant of barley seedlings against Cochliobolus salivas. Can. J. PI. Sci. 52: 949—953. Tempe, J. de 1964. Helminthosporium spp. in seeds of wheat, barley, oats and rye. Proc. Int. Seed Test. As- soc. 29; 117—140. Whittle, A.M. 1977. Cochliobolus salivas on barley in Scotland. PI. Path. 26: 67—74. —, & Richardson, M.J. 1978. Yield losses caused by Cochliobolus solivus on Clermont barley. Phytopath. Z. 91: 238—256. Ms received January 18, 1985 114 4 SELOSTUS Bipolaris sorokiniana-sienen merkitys ohran siemenlevintäisenä taudinaiheuttajana Suomessa Aarne Kurppa Helsingin yliopiston kasvipatologian laitos, 00710 HELSINKI 71* Ohran tyvi- ja lehtilaikkua aiheuttavan Bipolaris sorokiniana-sienen (syn. Heiminihosporium sativum, koteloaste Cochtiobolus sativus) merkitystä ohran sie- menlevintäisenä taudinaiheuttajana sekä sienen torjun- taa selvitettiin vuosina 1973—1979 Helsingin yliopiston kasvipatologian laitoksella järjestetyissä tutkimuksissa. Koesiemenenä käytettiin kenttäkokeella tuotettuja eri asteisesti (19 —92 %) infektoituneita, mutta muilta omi- naisuuksiltaan vastaavia siemeneriä ja Valtion Siemen- tarkastuslaitokselta tutkimuksiin valittuja siemeneriä. Erien sienitartunta tutkittiin mikroskooppisesti 7 vrk petrimaljoissa idätetyistä siemenistä. Orastuvuus määri- tettiin virallisen menetelmän mukaisesti. Peittausaineik- si sienen torjuntaan valittiin Ceresan- kuivapeittausjauhe (organoelohopea), Benlate (beno- myyli) ja Kemira Oy:n koe-erä imazalil-valmistetta. Tutkimukseen sisältyneet astiakokeet tehtiin Viikissä ja kenttäkokeet Viikissä sekä Inarissa Muddusniemen tutkimusasemalla. Orastuvuus astia- ja kenttäkokeissa laskettiin ohran 3—4-lehtiasteella. Kenttäkokeista otettiin laskennan yh- teydessä myös orasnäytteet (25 orasta/ruutu). Toiset näytteet koeruuduista otettiin hieman ennen maitotu- leentumisastetta. Näytteiden avulla pyrittiin varmista- maan B. sorokiniana-sienen osuus oireiden esiintymi- seen sekä seuraamaan taudin kehittymistä. Kasvustot korjattiin heti niiden tuleennuttua, Jyväsadot kuivattiin välittömästi, punnittiin ja niistä tehtiin sienimäärityk- set. Kylvösiemenen sienitartunta alensi ohran itävyyttä ja orastuvuutta; peittaamattomien koejäsenten orastuvuus aleni astiakokeissa keskimäärin 14 % ja kenttäkokeissa 18 %. Itävyyden ja vielä selvemmin orastuvuuden alene- minen riippuivat enemmän jyvien sisäosien sienitartun- nasta kuin jyvien määritetystä sienitartunnasta. Sieni esiintyi yleisemmin itämättömissä kuin itäneissä jyvissä. Kylvösiemenen peittaaminen organoelohopeavalmis- teella puhdisti pelkästään pinnallisen sienitartunnan saaneet siemenet, mutta ei täysin torjunut sientä sisä- osiltaan infektoituneista jyvistä, joiden itäessä kehittyi sairaita oraita. Systeeminen imazalil antoi paremman torjuntatuloksen kuin elohopea, mutta orastuvuus jäi silti alhaisemmaksi. Sieni aiheutti useimmissa kokeissa merkitseviä sato- tappioita sekä alensi kenttäkokeissa lisäksi sadon arvoa kylvösiemenenä, mikäli sääolot olivat suotuisat sienen sekundäärilevinnälle. Satotappiot astiakokeissa olivat 7.2 —38.5 % ja kenttäkokeissa s—ll5 —11 %, keskimäärin 6.3 %. Lajike-erot jäivät vähäisiksi, todennäköisenä syynä kaikkien lajikkeiden kylvösiemenen yhtäläinen, voimakas sienitartunta. Peittaaminen lisäsi satoja jon- kin verran, muttei tilastollisesti merkitsevästi. Peittaus- aineista organoelohopea kohotti satoa enemmän kuin imazalil, vaikkei pystynytkään torjumaan tautia täysin. Benomyyli todettiin peittausaineena täysin tehottomaksi sienen torjunnassa. Kylvösiemenen sienitartunta johti voimakkaan lehti- laikkutaudin puhkeamiseen kasvustossa tähkälletulon jälkeen kenttäkokeissa Muddusniemen tutkimusasemal- la Inarissa, missä sientä ei luontaisena esiinny. Epidemia johti myös jyväsadonsienitartuntaan. Sieni säilyi maas- sa satojätteissä kahden talvikauden yli ja kykeni infek- toimaan maalevintäisesti ohran oraita. Siemenlevintä on maassamme todennäköisesti B. sorokiniana-sienen tärkein säilymis- ja leviämismuoto. Sienen vahingollisuus ja leviämisvoimakkuus riippuvat kuitenkin paljolti kasvukauden säästä. Kuivana kasvu- kautena siemenlevintä johtaa pelkästään tyvitautiin, kosteana lisäksi lehtilaikkutautiin ja jyväsadonsienitar- tuntaan. * Nykyinen osoite: Kasvitautiosasto, MTTK, 31600 Jokioinen 115