Maataloustieteellinen Aikakauskirja Vol. 57: 85—96, 1985 Reaction of spring barley cultivars grown in Finland to soil-borne infection by Bipolaris sorokiniana and to its toxic metabolites AARNE KURPPA Department of Plant Pathology, University of Helsinki* SF-00710 HELSINKI 71, Finland Abstract. Soil-borne infection of Bipolaris sorokiniana caused foot and root rot in all spring barley cultivars studied. Significant differences in susceptibility of the cultivars and pathogenicity of the fungus isolates were found. Primary symptoms caused by the fungus were seedling blight, later foot and root rot. Yield losses caused by the fungus varied from 3 % to 33 % the mean being c. 15 %. Yield losses could occur without severe disease symp- toms. Toxic metabolites produced by the fungus induced visible foot and root symptoms in all cultivars tested and caused lesions in the leaves of some cultivars. Variability in toxin pro- duction of fungus isolates as well as the reaction of a cultivar to toxins was demonstrated. The cultivars most susceptible to soil-borne infection by the fungus also showed the most severe symptoms when exposed to toxic metabolites of the fungus. Introduction Bipolaris sorokiniana (Sacc. in Sorok.) Shoemaker, syn. Helminthospohum sativum (Pamm., King & Bakke), perfect state Coch- liobolus sativus (Ito & Kurib.) Drechsl. ex Dastur, the cause of common root rot, spot blotch and black point, is a world-wide pathogen of wheat and barley (Spraque 1950, Butler 1961, de Tempe 1964, Chulki- na 1972, Jorgensen 1974). The fungus is carried by air, soil and seed but in dry tempe- * Present address: Agricultural Research Centre, Department of Plant Pathology SF-31600 JOKIOI- NEN, Finland rate areas it is mainly soil-borne (Duczek & Piening 1982). Soil-borne inoculum becomes important if cereals, particularly barley and wheat are increasingly grown in crop rota- tion (Chinn 1976). Inoculum density in the soil is related to the amount of fungal spol- iation occurring on crop residues (Reis & Wunsche 1984). Under favourable condi- tions the conidia of B. sorokiniana may sur- vive several years in field soil (Ledingham 1970). Oil crops and fallow in crop rotation significantly decrease the number of germi- nating conidia in the soil (Chinn 1976). Yield losses of c. 10 % have been reported on barley (Piening et al. 1976, Stack 1982). Soil-borne infection may also cause over- Index words: Bipolaris sorokinicma, Helminthospohum sativum, Cochliobotus salivas, common root rot, barley 85 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=J-O4b4PrZ_NJOLjv.TpfZ03BHkdKLQSz6aAmmqA.q6ukTAkhmzGAGpOWW1sOAWh9RTo2KoDtUDD6EKKivFZ92X52rbfemXloI2Ips2dJPLmp6MyplOGYCz431ufdduk5yWaaCCXDUbf5cjAlWZ4dCHa_mb65BcqOCbE5tObQfCGST5IGKVEZA_tXSLT5JvMlYCA0KD1vRlw wintering damage on barley and wheat (Frank & Marshall 1981). Significant differences in reactions of bar- ley cultivars to the fungus have been found (Tinline & Ledingham 1979). Similarly vari- able pathogenicity among the fungus isolates has been reported (El-Nashaar & Stack 1982). In Finland the fungus is commonly found on the green barley crop (Mäkelä 1972, 1975) and seed crop (Kurppa 1975, 1984) and its importance as a soil-borne pathogen is obvious. However, little information is available about varietal reactions to soil- borne inoculum or pathogenicity of local fungus isolates. In addition to studying these problems the susceptibility of commercial barley cultivars to toxic metabolites pro- duced by the fungus isolates was investi- gated. Finally, these results and data from the infectivity tests at different developmental stages of barley crop were compared to evaluate the reaction of a cultivar to com- mon root rot. Material and methods A number of laboratory, greenhouse and field experiments were carried out to study obvious differences in susceptibility of spring barley cultivars to soil-borne infection of various isolates of Bipolaris sorokiniana. The effect of fungal metabolites on symptom appearance was also studied. In greenhouse experiments barley was grown in 25 X 25 cm size plastic pots in loamy field soil pH c. 6.0. In the first two ex- periments (Table 1) the soil was sterilized but was not sterilized for subsequent experi- ments unless stated otherwise. In the experi- ments studying the effects of fungal metabo- lites (Table 7), barley seedlings were raised in sterilized sand. Levels of fertilizer as recom- mended for the field crop were used to fer- tilize the soil. The soil for pot experiments was inoculated with homogenized fungal cul- tures grown 3 weeks on PDA in petri dishes at 22°C. Approximately one fungal culture in a 9 cm diameter petri dish was used per pot and carefully mixed with the soil before potting. Where necessary, the number of the reproductive fungal units in the homoge- nates was determined with a haemocyto- meter and the inoculum densities adjusted. Origin of fungal isolates were as follows: A leaves six-row barley cv. unknown Keitele, Central Finland B leaves two-row barley cv. Karri Lapinjärvi, Southern Finland C leaves spring wheat cv. unknown Loimaa, Southern Finland 6136 seed six-row barley cv. Etu Kuopio, Central Finland 6262 seed six-row barley cv. Suvi Mommila, Southern Finland 6571 seed six-row barley cv. Porno Kouvola, Southern Finland 7550 seed two-row barley cv. Birgitta Hämeenlinna, Southern Finland 8028 seed two-row barley cv. Karri Loimaa, Southern Finland All experiments were replicated four times. For short term pot experiments 50 seeds were sown in each pot, otherwise 30 seeds were sown. The first short term experi- ments were designed to determine the effect of soil-borne infection on seedling emer- gence, early foot and root rot and foliar symptom development, and growth rate of young seedlings. After visual symptom ob- servation, basal stems and roots of five seed- lings showing symptoms were surface steril- ized wich 1 % Na-hypochloride and placed on cornmeal agar containing 50 ppm strepto- mycin. Fungal growth was observed with a stereomicroscope after one and two weeks of incubation at 22°C. The long term experiments were designed to test the true pathogenicity of the fungus isolates to different barley cultivars as measured by the development of barley and grain yield. In the experiments detailed in tables 2 and 3 the soil was inoculated with 86 the fungus for the first year’s study as de- scribed earlier. For the second year’s experi- ments the pots were left after harvest in a covered store outdoors to overwinter. The following spring the soils in the pots were homogenized and mixed keeping each treat- ment separate. The soil lots were fertilized but no extra inoculum were added. These ex- periments were carried out in a partially covered greenhouse where the temperature and relative humidity were comparable to the conditions outdoors. Subsamples of grain from each cultivar and treatment were also examined for the incidence of B. soroki- niana in the seeds. The inoculum potential of naturally in- fested field soil was studied in the field and in greenhouse experiments. In the field only symptom appearance and development and the fungus incidence in the seeds were studied but in greenhouse experiments disease development was followed at short intervals from seedling emergence to harvest. Soil for the experiments was taken from a field plot where soil-borne and seed-borne infections by B. sorokiniana were studied during two previous growing seasons. Con- trol soil was taken from the same field area, where non-infected barley crop was grown. Control of soil-borne infection by or- ganomercurial seed treatment was also studied. The seeds were treated with Ceresan seed dressing powder, 2 g powder/1 kg of seeds. Up to five plants showing symptoms / pot, if available, were tested for the infection of B. sorokiniana as described earlier. In order to observe fungal invasion into the upper shoot a portion was surface sterilized in 1 % Na-hypochloride and cut into parts of 5 cm, which were then placed in order on the agar. Fungal growth was observed one week later with a stereomicroscope. The incidence of B. sorokiniana in grain yields was determined as described by Kurppa (1984). Three experiments were carried out to determine the response of some barley culti- vars to the metabolites of the fungus isolates. The medium containing fungal metabolites was produced by culturing fungus isolates 30 days in erlenmeyer bottles in liquid Zapek Dox medium. The medium was then filtered through filter paper followed by filtration through a 45 micron filter. Samples of these filtrates were autoclaved before dilution in fresh Zapek Dox medium. Susceptibility of five barley cultivars to phytotoxins produced by nine fungus iso- lates was studied in the first experiment (Fig. 3). Eight day old barley seedlings raised in sterilized sand were cut at the coleoptile and the shoots were placed into 50 ml erlenmeyer bottles filled with 30 ml of differentially diluted media from fungal cultures (see Gayed 1962). The shoots in the bottles were exposed for 5000 lux fluorescent light 18 h/day and the symptoms in the seedlings were observed after 6, 24, 48 and 72 hours. For the second experiment (Table 5) barley seedlings grown on sterilized sand were care- fully and gently washed to remove the sand, dried for 5 minutes on filter paper and weigh- ed. Before placing into the bottles filled with medium the seedlings were rinsed in sterile distilled water. After three days of incuba- tion under 5000 lux illumination 18 h/day at 22° C the experiment was discontinued and the seedlings were reweighed. Finally, barley was grown in sterilized sand, which was watered the first week with sterile Zapek Dox medium. During the re- maining two weeks, filtered medium con- taining fungal metabolites was used for watering the seedlings. The seedlings were then gently washed out of sand, weighed and observed for the presense of symptoms. All data were subjected to analysis of vari- ance. Results Spring barley seedlings, growing in soil naturally infested or artificially inoculated with B. sorokiniana, became readily infected 87 Table 1. The effect of Bipolaris sorokiniana inoculum in sterilized loam soil on foot and root injuries (a) and fresh weight of seedling crop/pot (b) after 32 days growing period in laboratory experiments. Fungus a P er cent 'n J ul "i es isolate' Cultivar and inoculum density Paavo Ingrid Mean of 10°* 10-' 10-2 Mean 10° 10-' 10-2 Mean the isolate A 81.5 60.5 24.5 55.0 74.5 39.0 24.5 46.0 50.5 B 83.0 54.6 17.0 51.5 85.6 62.0 30.5 60.0 55.7 C 77.0 34.6 22.0 44.5 60.5 40.0 23.5 41.3 42.9 Mean 80.5 49.9 21.2 73.5 47.0 26.1 1 For origin of isolate see text * Inoculum density 10° = c. 1 000 000 reproductive units/1 liter soil F-values: Inoculum density = 134.0™, LSD, OOS = 8.1 % Inoculum isolate = 7.4», = 6.1 % b Fresh weight of seedlings g/pot Paavo Ingrid Control Control Mean of 10° 10-' 10- 2 Mean 10° 10-' 10-2 Mean the isolate 34.8 45.2 A 28.4 28.0 31.6 29.3 39.8 40.2 42.0 40.7 35.0 B 27.5 28.4 31.9 29.3 37.0 38.3 41.7 39.0 34.1 C 28.7 30.0 31.1 29.9 38.4 40.3 42.1 40.3 35.1 Mean 28.2 28.8 31.5 38.4 39.6 41.9 F-values: Inoculum density = 8.1” 1, LSD tOO5 = 1 1.0 % (Paavo 3.83 g, Ingrid 4.97 g) Inoculum isolate < 1 by the fungus in pot or field experiments. The fungus was extremely pathogenic to bar- ley in sterilized field soil. Most seedlings of the two barley cultivars (Table 1) in the ex- periments became infected when the inocu- lum density was c. 1 million reproductive units per liter of soil, but a 100-fold reduc- tion in inoculum density also resulted in a high rate of infection and injury (Table 1 a.). The seedlings showed dark brown coleoptiles and root discoloration as well as longidual or oval dark brown lesions on the basal leaves. All crops in inoculated soils showed poor growth two to three weeks after emergence. When the seedlings were weighed five weeks after sowing, a significant growth reduction was found (Table 1 b.). The inoculum den- sity was of major importance and fungus iso- late or barley cultivar played a minor role. The mean weights of single seedlings re- mained significantly lower than those of controls but more biomass reduction was due to a lower number of seedlings per pot. The fungus also significantly reduced the emergence of most of the 12 barley cultivars tested in non-sterilized loamy field soil. All barley cultivars showed foot discoloration and seedling blight with significant dif- ferences among them in the incidence and severity of disease (Table 2). Six-row culti- vars Paavo, Porno and Teemu were highly susceptible to foot discoloration and seedling blight but two-row cvs Ingrid and Karri as well as six-row cvs Otra, Suvi and Tammi appear to have some resistance. The following summer, after natural over- wintering of the soils, a similar reduction in the emergence and symptom appearance was found. All fungus isolates retained their in- fectivity in soil but some reduction in their pathogenicity was obvious (Table 2). The isolate 7550 was particularly pathogenic. 88 Table 2. The effect of soil-borne infection by Bipolaris sorokiniana on per cent emergenceand injured seedlings of 12 spring barley cultivars in covered pot experiments 1" year's experiment 1 2nd year's experiment Cultivar Isolate Isolate Controls 6136 6571 7550 Means w/o Controls 6136 6571 7550 Means w/o controls controls A 2 BABABABAB ABABABABAB Eero 99 0.0 96 11.4 94 12.8 93 15.0 94.3 13.1 98 0.0 96 10.4 96 10.4 92 15.2 94.7 12.0 Etu 99 0.0 97 13.4 96 14.9 94 13.8 95.7 14.0 98 0.0 93 10.8 88 14.8 89 10.1 90.0 11.9 Hja 673 97 0.0 95 7.4 95 11.7 93 15.0 94.3 11.3 97 0.0 96 4.2 96 8.3 92 14.1 94.7 8.9 Ingrid 96 0.0 95 3.1 95 3.1 91 4.4 93.7 3.5 96 0.0 95 1.0 96 5.2 95 2.1 95.3 2.8 Karri 96 0.0 94 4.2 94 6.2 92 9.8 93.3 6.7 96 0.0 96 2.1 97 4.1 93 7.5 95.3 4.6 Otra 95 0.0 96 7.3 94 8.5 92 12.0 94.0 9.3 96 0.0 93 6.4 93 5.4 90 7.3 92.0 6.4 Paavo 97 0.0 92 18.5 92 23.9 90 24.4 91.3 22.7 97 0.0 93 14.0 93 14.0 90 33.3 92.0 20.4 Pomo 87 2.3 84 16.8 84 22.6 80 25.0 82.7 21.5 94 0.0 91 13.2 89 13.5 87 21.8 89.0 16.2 Pirkka 95 0.0 91 6.6 91 10.0 89 10.1 90.3 8.9 95 0.0 93 4.3 93 6.5 89 9.0 91.7 6.6 Suvi 98 0.0 96 5.5 90 7.8 95 6.3 93.7 6.5 98 0.0 96 4.2 93 8.6 95 6.3 94.7 6.4 Tammi 94 0.0 94 3.1 94 11.7 94 11.7 94.0 8.8 96 0.0 96 1.0 94 6.4 93 9.7 94.7 5.7 Teemu 96 0.0 94 18.1 94 30.8 92 32.6 93.3 27.1 97 0.0 93 14.0 93 12.9 89 24.7 91.7 17.2 Means 95.8 0.2 93.7 9.6 92.7 13.7 91.2 15.0 92.6 12.8 96.3 0.0 94.3 7.1 93.4 8.7 91.2 13.4 92.9 9.9 1 For l sl year's experiment unsterilized loamy soil was inoculated with the fungus two weeks before sowing the seeds. The pots wereresownthe following summerbut no extra inoculum was added. 2 A = "to emergence;B = % visibly injured seedlings F-values: I" year's experiment 2 nd year's experiment Emergence / treatments = 47.3", LSD, 00S = 1.47 % Emergence / treatments = 27.1", LSD tOOS = 1.44 % » / cultivars = 8.0", = 1.90 % » / cultivars = 5.7", = 1.78 % Injuries (w/o controls) / treatments = 17.5", = 2.33 % Injuries (w/o controls) / treatments = 31.5", = 1.99 % » » / cultivars = 29.3", = 2.97 % » —» — / cultivars = 28.9", = 2.54 % S9 Table 3. The effect of soil-borne infection by Bipolaris sorokiniana on the relative number of grain producing heads and the relative giain yield of 12 barley cultivars in covered pot experiments. I sl year's experiment 1 2 nd year's experiment Cultivar Isolate Isolate 6136 6571 7550 Means w/o 6136 6571 7550 Means w/o controls controls C2DCD CD CD CD CD CD CD Eero 102.8 88.2 110.6 80.0 98.1 81.3 103.8 83.1 100.9 91.0 96.4 85.0 96.4 81.4 97.9 85.8 Etu 104.3 94.7 94.6 97.8 104.3 85.7 101.0 92.7 92.5 91.4 87.8 82.8 92.5 79.5 90.9 84.6 Hja 673 88.3 96.6 85.4 89.7 89.3 81.9 87.7 89.4 100.0 97.2 98.1 85.4 91.6 74.3 96.6 85.6 Ingrid 103.4 86.3 113.8 77.1 87.8 72.5 101.7 78.6 100.0 94.4 100.7 89.1 99.2 75.8 100.0 86.5 Karri 104.9 90.9 88.4 82.3 81.7 80.5 92.0 84.4 105.6 95.4 97.5 90.8 89.4 87.8 97.5 91.3 Otra 89.2 89.9 92.1 78.2 82.3 75.6 87.8 81.2 95.3 93.2 94.3 89.8 86.0 81.0 91.9 88.0 Paavo 88.4 80.3 88.5 65.6 68.4 62.3 81.8 69.4 91.2 92.4 81.3 81.7 75.5 67.9 82.7 80.7 Pomo 91.9 73.7 87.8 64.2 77.0 53.3 85.6 63.7 94.1 89.7 89.2 82.4 81.4 69.1 88.2 80.4 Pirkka 91.1 90.7 85.1 75.6 78.2 64.0 84.8 76.8 93.6 90.2 92.7 91.7 89.1 83.0 91.6 88.3 Suvi 103.0 97.8 83.5 88.4 94.8 94.6 93.7 93.6 100.0 95.7 87.0 85.3 88.9 81.0 92.0 87.3 Tammi 103.1 100.9 88.5 92.4 100.0 99.9 97.2 98.7 100.9 100.7 99.0 94.2 97.2 69.9 99.0 94.9 Teemu 83.1 67.4 74.1 64.4 67.4 45.9 74.9 59.2 87.0 82.8 84.2 76.1 75.9 66.9 82.3 75.3 Means 96.1 88.1 91.1 80.4 85.8 74.7 96.8 92.8 92.3 85.4 88.6 76.5 1 For details see table 2. 2 C = Number of grain producing heads; D = grain yield as relative value of control as 100.0. F-values: 1" year's experiment 2 nd year's experiment Heads / treatments = 6.46", LSD, 00 , = 7.09 % Heads / treatments = 18.2", LSD tOOS = 3.33 % » / cultivars = 5.72", = 9.09 % » / cultivars = 9.6", = 4.27 % Yield / treatments = 28.82", = 2.31 % Yield / treatments = 73.34", = 4.14 % » / cultivars = 6.30", = 3.01 % » / cultivars = 2.78* , = 5.46 % 90 Varietal susceptibility to the fungus re- mained unchanged from the previous experi- ment. In these two experiments soil-borne in- fection by B. sorokiniana significantly de- creased the number of grain-carrying heads and simultaneously the grain yield of most cultivars (Table 3). The yields of cultivars with highest symptom incidence were the most severely affected by the fungus. How- ever, significant losses were also associated with cultivars with mild disease symptoms. These cultivars include Eero, Ingrid and Pirkka. Similarly, naturally infested field soil in- fected all 16 spring barley cultivars tested in pot experiments. Symptom incidence and severity after four weeks growth in infested soil varied significantly between the cul- tivars. Among the cultivars not earlier tested, Aapo and Eva (two-row cvs) were re- sistant but Birgitta (two-row) and Vigdis (six-row) were susceptible (Fig. 1, F = 17.8**, LSD, OOS = 3.7 %). The fungus also caused noticeable growth reduction in the experiments (Table 4); bar- ley grown in infested soils remained 10—15 cm shorter than those in control soils. Yield loss averaged 24 %. An organomercurial seed dressing compound gave a slight yield increase, but did not protect the young seed- lings from becoming infected. No infection of upper leaves or heads was found in any of the experiments when soil-borne infection was studied in relatively dry greenhouse con- ditions. In the field the symptoms caused by the fungus were comparable to those in green- house experiments. The first seedling blight symptoms were found 2 to 3 weeks after sowing, depending on the temperature. Some increase in symptom incidence was found during the following weeks but no further foliar symptoms occurred during dry growing seasons when spore liberation from the secondary infection sources was mini- mal. In these conditions the fungus was localized in roots, basal stems and the lower senesceting leaves and was never found in upper leaves, upper shoot or heads. The foot and root rot symptoms, however, remained typical of the fungus even in these excep- Table 4, The yield loss caused by natural soil-borne infection by Bipolaris sorokiniana on barley cvs. Birgitta and Otra in greenhouse experiments and the control of the fungus by mercurial seed treatment. Cultivar Birgitta Otra Mean Untreated Treated Untreated Treated Untreated Treated Control soil 100.0* 98.6 100.0 102.1 100.0 100.4 Infected soil 70.4 79.6 81.9 85.5 76.2 82.5 * Yields reported relative to control as 100.0 F-values: Soil = 145.5", LSD, OOi = 5.5 % Seed treatment = 9.8", = 7.9 % Fig. 1. Per cent seedlings of 16 barley cultivars showing symptoms induced by natural soil- borne infection by Bipolaris sorokiniana in greenhouse experiments after 4 weeks growth. 91 tionally dry conditions (Fig. 2). Barley cul- tivars, which were found susceptible in pot experiments were also susceptible in the field but no data is presented because of the uneven distribution of the fungus in the field soil. Metabolic products of B. sorokiniana con- taining phytotoxins were shown to be responsible for symptom appearance and decreased growth rate of barley seedlings (Fig. 3). The toxic effect was found whether barley seedlings were grown in toxin-con- taining liquid medium or in sand watered with this medium. In liquid medium the growth of barley seedlings was minimal during the three days period they were ex- posed to toxins (Table 5). Dilution of 5 x 10~3 from the filtered culture fluid was capable of inducing visible symptoms of leaf senescence and foot discoloration with a combination of growth decrease. Significant differences between barley cultivars and fun- gus isolates were found. The average per cent varietal growth inhibition originating from the toxic metabolites was as follows: Birgitta 17.6, Karri 25.2, Otra 26.7 and Paavo 31.2. Susceptibility to the toxins was comparable to that caused by soil-borne infection of the fungus. Autoclaved medium remained high- ly toxic. Severe foot and root discoloration symp- toms were found in young seedlings of all barley cultivars tested growing in sterilized sand after they were watered two weeks with medium containing filtered fungus culture fluid (Table 6). The culture metabolites from one fungus isolate induced significantly higher symptom incidence than any of the other isolates tested and similarly two barley cultivars were found to be more susceptible than the rest. Some interaction between the toxin source and the barley cultivar was also obvious. Toxic metabolites decreased growth rate of all cultivars (Table 7). However, dif- ferences were found: cv. Birgitta being the most susceptible and cv. Otra the most resist- ant. Fig. 2. Foot rot symptoms at the time of heading Fig. 3. Leaf dip senescence and root discoloration caused by toxic metabolites of Bipolaris sorokiniana. 92 Table 5. The effect of toxic metabolites produced by Bipolaris sorokiniana on relative growth rate of barley seed- lings during three days growing period in liquid Zapek Dox medium. a. Non-autoclaved toxic medium Isolate 1 10 1 dilution Isolate 5 x 10~3 dilution Mean w/o Cultivar 6136 6262 6571 7550 8028 Control 6136 6262 6571 7550 8028 control Birgitta Karri Otra Paavo Mean 20.7 21.6 12.6 17.1 12.8 b. Autoclaved toxic medium Birgitta 21.6* 25.1 14.6 9.1 7.2 28.9 29.1 17.8 19.8 24.3 19.7 Karri 13.2 9.6 4.1 4.1 6.1 20.9 15.3 6.1 10.6 13.9 10.4 Otra 14.1 21.0 6.4 8.0 3.7 17.4 19.6 19.9 12.2 24.7 14.7 Paavo 14.1 9.4 5.7 1.4 2.6 26.4 19.7 10.4 9.0 8.5 10.7 Mean 15.7 16.3 7.7 5.6 4.9 23.4 20.9 13.6 12.9 17.6 Mean(a +b) 13.0 17.6 8.3 5.1 3.7 38.6 22.0 21.3 13.2 15.0 15.2 1 Toxin source * Relative weight increase of seedlings (%) F-values: Toxin source = 55.8XX , LSDl00! = 7.1 % Barley cultivar = 19.3XX , = 7.7 % Table 6. Per cent seedlings showing root symptoms after three weeks growth in sterilized sand watered last two weeks with Zapek Dox medium containing metabolites produced by Bipolaris sorokiniana isolates. Cultivar Isolate Mean w/o Control 6136 6262 6571 7550 8028 control Birgitta o.o* 5.0 22.5 0.0 7.5 90.0 25.0 Karri 0.0 17.5 12.5 2.5 32.5 17.5 16.5 Otra 0.0 2.5 2.5 12.5 5.0 27.5 10.0 Paavo 0.0 22.5 35.0 57.5 32.5 57.5 41.0 Mean 0.0 11.9 18.1 18.1 19.4 48.1 * Seedlings showing root symptoms (%) F-values: Toxin producing isolate = 4.6% LSD 100! = 13.3 "In Barley cultivar = 5.0», = 14.8 % Table 7. The relative fresh weight of barley seedlings after three weeks growth in sterilized sand watered last two weeks with Zapek Dox medium containing metabolites produced by Bipolaris sorokiniana isolates. Cultivar Isolate Mean w/o 6136 6262 6571 7550 8028 control Birgitta 81.4* 69.6 74.7 79.1 66.2 74.2 Karri 77.4 79.0 88.1 79.7 79.7 80.8 Otra 85.2 98.1 89.0 93.2 89.3 91.0 Paavo 76.6 80.7 79.3 85.2 78.0 80.0 Mean 80.2 81.9 82.8 84.3 78.3 * Relative fresh weight. Controls for each cultivar = 100.0 F-values: Barley cultivar = 10.3X\ LSDl00! = 8.3 % Toxin producing isolate < 1 93 11.8* 14.7 2.6 8.9 1.8 33.3 10.3 12.8 10.7 3.7 1.3 36.3 16.2 23.4 9.1 3.7 5.0 41.7 3.0 24.8 13.1 1.4 1.7 43.2 10.3 18.9 8.8 4.4 2.4 38.6 15.7 19.1 11.8 16.1 14.6 11.7 15.5 20.5 13.4 16.1 13.5 11.8 27.9 25.3 9.8 22.7 9.4 15.2 23.9 21.7 15.4 13.6 13.5 13.2 Discussion Differences in resistance of barley culti- vars to common root rot have been widely reported but the incidence and severity of visible symptoms has not always been com- parable to yield losses as reported by Piening (1973), Tinline and Ledingham (1979) and Stack (1982). In this study severe disease reaction was usually followed by severe yield reduction but high yield losses were also found without visible symptoms. Genetically inherited susceptibility to com- mon root rot in certain Finnish six-row bar- ley cultivars, such as Paavo and its relatives, appears to be dominant, but some resistance to the disease is obvious in some cultivars. The cultivars now shown to be highly sus- ceptible to soil-borne infection have pre- viously been shown by Kurppa (1984) to car- ry the highest rate of seed infection. High in- cidences in seedling symptoms and injuries were always followed by high root rot in- cidence differing in this respect to the results reported by Stack (1981). The number of grain producing heads/pot has been used to estimate or forecast yield. According to Ver- ma et al. (1973), the number of heads/plant is greatly affected by root rot, which agrees with this study. Lutz et al. (1983) have, however, reported number of kernels per head and particularly dry weight of kernels are the primary effects of the disease. Variation in pathogenicity of different References Butler, F.C. 1961. Root and foot rot disease of wheat. Sci Bull. No 77, New South Wales Dept Agric. Chinn, S.H.F. 1976. Cochliobolus salivas conidia populations in soils following various cereal crops. Phytopath. 66: 1082—1084. Chulkina, V.A. 1972. Soil infestation and some meth- ods for its suppression in the control of common root rot of barley. A translation of Mikologiya i fito- patologiya 6: 435 —439. Davis, C.M., Christ, J.E., Pueppke, S.G. & Stack, fungus isolates has also been reported by El-Nashaar and Stack (1982). However, the average pathogenicity of the isolates in various localities was similar. It follows that for a cultivar to be field resistant it must have wide-scale resistance to the fungus. Metabolites on B. sorokiniana toxic to barley seedlings have been reported as early as the 1950’s by Ludwig (1957) but ac- cording to Dutrecq et al. (1980) no definite answer has yet been given whether toxin- resistant plants will also be resistant to infec- tion by the fungus. In this study most barley cultivars showing high susceptibility to toxic metabolites were also more susceptible to in- fection by the fungus. However, it is possible that the variability in the toxins reported by Davis et al. (1982) was not present in this study. B. sorokiniana is a world-wide pathogen of cereals of such importance that all avail- able resistance against it, as developed by plant breeding as reported by Wilcoxson et al. (1980) should be used. It would appear that the reaction to toxic metabolites of B. sorokiniana could be used to screen barley breeding lines for susceptibility to common root rot before submitting promising lines to infection tests. Acknowledgements. I am grateful to Dr. FES. Pepin for invaluable recommendations and revision of the English text. R.W. 1982. A bioassay for toxic metabolites of Hel- minlhosporium sativum. Phytopath. 72: 1134. Duczek, L.J. & Piening, L.E. 1982. Effect of seeding dept, seeding date and seed size on common root rot of spring barley. Can. J. PI. Sci. 62: 885—891. Dutrecq, A., Sommereyns, G. & Semal, J. 1978. Using resistance to the toxin of Helminlhosporium sativum as a means of selecting cereals: toxicity tests and toxin preparation. Ann. Appi. Biol. 89: 370—373. El-Nashaar, H.M. & Stack, R.W. 1982. Pathogenic 94 variation in populations of Helminthosporium sati- vum. Phytopath. 72: 1135. Frank, J.A. & Marshall, H.G. 1982. The influence of root rot on the winter survival of wheat and barley plants. Phytopath. 72: 260. Gated, S.K. 1961. Production of symptoms of barley leafspot disease by culture filtrate of Helminthospo- rium sativum. Nature, Lond. 191; 725—726. - 1962. The pathogenicity of six strains of Helmin- thosporium sativum to three cereals with special reference to barley. Mycopath. 18: 271—279. Jorgensen, J. 1974. Occurence and importance of seed borne inoculum of Cochliobolus sativus in Denmark. Acta Agric. Scand. 24: 49—54. Kurppa, A. 1975. Ohran tyvi- ja lehtilaikku yleistyvä piilevä kasvitauti. Käytännön Maamies 1975, 7; 20—21. 1984. Bipolaris sorokiniana on barley seed in Fin- land. J. Agric. Sci. Finl. 56: 175—181. Ledingham, R.J. 1970. Survival of Cochliobolussativus conidia in pure culture and in natural soil at different relative humidities. Can. J. Bot. 48: 1893—1896. Ludwig, R.A. 1957. Toxin production by Helmintho- sporium sativum P., K. & B. and its significance in disease development. Can. J. Bot. 35: 291—303. Lutz, A., Van Aleen, N.K. & Kidambi R. 1983. The role of Helminthosporium sativum in barley crown rot and yield loss. Phytopath, 73: 960. Mäkelä, K. 1972. Leaf spot fungi on barley in Finland. Acta Agric. Fenn. 124: 1—33. 1975. Occurence of Helminthosporium species on cereals in Finland in 1971—1973. J. Sci. Agric. Soc. Finl. 47: 181—217. Pienino, L.J. 1973. Differential yield response of ten barley cultivars to common root rot. Can. J. PI. Sci. 53: 763—764. —, Atkinson, T.G., Horricks, J.S., Ledingham, R.J., Mills, J.T. & Tinline, R.D. 1976. Barley losses due to common root rot in the Prairie Provinces of Cana- da, 1970—1972. Can. PI. Dis. Surv. 56: 41—45. Reis, E.R. Wunsche, W.A. 1984. Sporulation of Coch- liobolus sativus on residues of winter crops and its relationship to the increase of inoculum density in soil. PI. Dis. 68: 411—412. Spraque, R. 1950. Diseases of cereals and grasses in North America. 538 p. New York. Stack, R.W. 1981. Seedling disease responce not a good indication of adult plant susceptibility to Hel- minthosporium root rot. Phytopath. 71: 257. 1982. Yield losses in spring barley due to common root rot in Eastern North Dakota. Phytopath. 72: 1139—1140. Tempe, J. de. 1964. Helminthosporium spp. in seeds of wheat, barley, oats and rye. Proc. Int. Seed Test. Assoc. 29: 117—140. Tinline, R.D. & Ledingham, R.J. 1979. Yield losses in wheat and barley cultivars from common root rot in field tests. Can. J. PI. Sci. 59: 313—320. Verma, P.R., Morrall, R.A.A. & Tinline, R.D. 1973. Root rot disease of wheat in a cultivated ecosystem. Tech. Report, Matador Project, Univ. of Sascatchewan No 30, 221 p. Wilcoxson, R.D., Rasmusson, D.C., Banttari, E.E. & Johnson, D.A. 1980. Feasibility of selecting for re- sistance to kernel discoloration in barley. PI. Dis. 64: 928—930. Ms received January 18, 1985 95 SELOSTUS Suomessa viljeltyjen ohralajikkeiden alttius Bipolaris sorokiniana-sienen maalevintäiselle tartunnalle ja sienen toksisille aineenvaihduntatuotteille Aarne Kurppa Helsingin yliopiston kasvipatologian taitos, 00710 Helsinki 71* Ohran tyvi- ja lehtilaikkua aiheuttavan Bipolaris sorokiniana-sienen (syn. Helminthosporium sativum, koteloaste Cochliobolus salivus) vahingollisuutta maa- levintäisenä taudinaiheuttajanatutkittiin Helsingin ylio- piston kasvipatologian laitoksella vuosina 1973—1979. Erityishuomio tutkimuksissa kohdistettiin ohralajikkei- den reagointiin sieneen ja sen toksisiin aineenvaihdunta- tuotteisiin. Pyrkimyksenä oli myös etsiä luotettavia, in- fektointikokeita yksinkertaisempia menetelmiä ohrala- jikkeiden taudinkestävyyden toteamiseksi. Astiakokeet tehtiin kasvihuoneessa tai kasvukausien aikana sateelta suojatussa ulkotilassa. Kasvualustana oli peltoraulta, mikä oli sienen luontaisesti infektoimaa tai mihin sienikasvusto oli lisätty. Aineenvaihduntatuottei- den toksisuutta selvittävissä kokeissa sieni kasvatettiin Zapek-dox ravintoliuoksessa, mitä suodatettuna sa- maan ravintoliuokseen laimennettuna käytettiin ohran oraiden kasvatukseen erlenmeyerpulloissa tai oraiden kasteluun hiekkakasvatuksissa. B. sorokiniana aiheutti tyvi- ja juurilaikkuja sekä myös koko maanalaisen versonosan ruskettumista ja kuivettumista kaikissa tutkituissa lajikkeissa. Ensim- mäisinä oireina astia- ja kenttäkokeissa havaittiin tum- manruskeita pitkulaisia lehtilaikkuja heti orastumisen jälkeen. Kasvun edistyttyä sieni ei enää levinnyt ylem- mäksi versoon eikä injektoinut muodostuvaa jyväsatoa korrensisäisesti kasvamalla, mutta tyvitautioireet vah- vistuivat ja niihin liittyen verson kasvu sekä sadonmuo- dostus jäivät heikoksi. Lajike-erot olivat suuria ja ne säilyivät samansuuntai- sina eri tavoin järjestetyissä kokeissa. Sieni aiheutti voi- makkaimmat tyvitautioireet lajikkeissa Teemu, Paavo ja Pomo sekä lievimmät lajikkeissa Aapo, Ingrid ja Tammi. Sienen aiheuttama satotappio vaihteli 3 Voista (Tammi) 33 Veliin (Teemu) ollen keskimäärin noin 15 Vo. Sieni aiheutti monitahoisissa lajikkeissa kes- kimäärin pahempaa vioitusta kuin kaksitahoisissa. Kyl- vösiemenen peittaaminen ei suojannut nuorta orasta sie- nitartunnalta, mutta saattoi viivästyttää sitä jossain määrin. Sienen aineenvaihduntatuotteina syntyvät toksiinit ai- heuttivat juuri- ja tyvioireita kaikissa tutkituissa lajik- keissa, joissakin lisäksi myös lehtioireita. Ohralajikkei- den reagointierot toksiineihin samoin kuin tok- siini-isolaattien erot olivat samansuuntaisia, mitä infek- tiokokein todettiin. Oraan voimakas reagoiminen tok- siineihin paljasti useimmiten lajikkeen tai linjan alttiu- den myös sieni-infektiolle. Ohran tyvi- ja lehtilaikkusientä on pidettävä maas- samme vakavana taudinaiheuttajana. Sieni on oloissam- me pääasiallisesti siemen- ja ilmalevintäinen, mutta sitä kertyy maahan tyvitaudinaiheuttajaksi lisääntyvästi eri- tyisesti ohran satojätteissä. Tätä kertymistä voidaan es- tää helpoimmin käyttämällä viljelykiertoa, peittaamalla kylvösiemen elohopeapitoisella tai sopivalla systeemisel- lä valmisteella ja kulottamalla puidun ohrakasvuston sänki ennen kyntöä. * Nykyinen osoite Kasvitautiosasto, MTTK, 31600 Jokioinen 96