Maataloustieteellinen Aikakauskirja Vol. 57: 97—105, 1985 The response of some spring barley cultivars grown in Finland to air-borne secondary infection by Bipolaris sorokiniana AARNE KURPPA Department of Plant Pathology, University of Helsinki * SF-00710 HELSINKI 71, Finland Abstract. Air-borne secondary inoculum of Bipolaris sorokiniana caused severe foliar dis- eases and yield losses in all 12spring barley cultivars tested in greenhouses or in the field. For secondary infection to occur a high relative humidity was necessary. Yield losses due to foliar diseases reached a maximum of 43.4 % in greenhouse experiments and 27.8 % in the field. The mean losses were 20.3 % and 12.3 %, respectively. Early infection at the time of heading or shortly after it resulted in higher yield losses than did later infection, although the symptom expression was opposite. Spore inoculation or natural secondary infection by the spores from a diseased crop after heading always resulted in a high infection incidence in the grain. Infec- tion incidence as well as fungal invasion of the internal cell leyers of the grains varied signifi- cantly among barley cultivars. The most susceptible of those tested were cvs. Teemu, Paavo and Pomo, while the most resistant were Ingrid, Otra and Pirkka. Introduction Bipolaris sorokiniana (Sacc. in Sorok.) Shoem. (syn. Helminlhosporium sativum Pamm., King & Bakke), perfect state Cochlio- bolus sativus (Ito & Kurib.) has a world-wide distribution as a major pathogen of cereals (Spraque 1950). Yield losses in barley of higher than 10 per cent have been reported recently by Piening (1973) and Stack (1982). In addition the fungus has been found to be � Present address: Agricultural Research Centre, Department of Plant Pathology SF-31600 JOKIOINEN, Finland increasingly common in barley in the cool climate in North-Western Europe (Jorgen- sen 1974, Hewett 1975, Mäkelä 1975, Kurppa 1984). Conidia of the fungus are the main sources of infection, and are able to survive at least two years in soil (Ledingham 1970). Infec- tion caused by spore liberation from plant debris is strongly related to the previous crop in the field (Chinn 1976, Reis & Wunsche 1984). Important sources for spore liberation also include basal stems, lower leaves and subcrown intenodes of diseased host plants (Mead 1942, Chinn 1977). Conditions for Index words: Bipolaris sorokiniana, Helminlhosporiumsativum, Cochliobolus sativus, barley diseases, leaf blotch, headblight 97 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=EwF2xPE2MnffXAwe.ItOow_nCOj0P4TBG4eGw4A.BOkGcT5EiRNu-kUglYBsI0aWawWbGVEG_LyG4o2_YR3pkoCthQ3CxGpJVIgNOokCeoT3CRX2_gBoQH1rfZJ9b386wVcMEH6cNnLRF61R7juwfzLYwbF5BBlIkvUrb43fJmE57D4PapnLxPFzWyznWljA9r-OIAxLacw the occurrence of secondary infection of bar- ley are most favourable during the late growing season, when crops are nearly ripe and relative humidity is high for at least part of the day (Spurr & Kiesling 1961, Chulki- na 1972). Air-borne secondary infection may result in leaf spots and blotches, and head- blight as well as infection in ripening seeds (Mead 1942, Vendrig 1956). Materials and methods Experiments to study the response of bar- ley cultivars to secondary infection of B. so- rokiniana were conducted mainly in green- houses, but one field experiments was done as well. Additional interests of the study were the significance of the barley developmental stage at the time of infection as well as the role of the fungus isolate in inducing infec- tion and foliar disease. The seeds used for sowing in the experi- ments were all dressed with organomercurial seed dressing powder, 2 g/kg. In greenhouse experiments 25 x 25 cm pots filled with non-sterile fertilized loamy field soil were sown to obtain at least 50 normally devel- oped seedlings per pot. Approximately three weeks after sowing excess plants were rogued to leave 35 or 50 seedlings. For watering an equal volume of water was added to each pot. Extra fertilizer (N-P-K, containing es- sential microelements) was given twice at seedling stages during watering. The field ex- periment was sown in treatment blocks with plot sizes of 6.65 m 2, each block consisting of four cultivars and four replicates. The blocks were separated from each other with a belt of oats three meters wide, to prevent spore carry-over during spraying and short distance contamination later from the treated blocks. The fungus isolates used for spore inocu- lum had the following origins: 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 D seed six-row barley cv. Porno Helsinki, Southern Finland E seed oats cv. Hannes Maaninka, Central Finland 7550 seed two-row barley cv. Birgitta Hämeenlinna, Southern Finland The inoculum was prepared from fungal colonies grown three weeks on potato dex- trose agar (PDA) in petri dishes at 22°C, by homogenizing in distilled water to make a suspension containing c. 104 spores/ml (see Anderson & Banttari 1976). Barley was sprayed with 10 ml/pot in greenhouse experi- ments and 94 ml/m2 in the field. After this treatment the pots were incubated for 48 hours in a plastic tent with a relative humidi- ty of 90—100 ®/o and temperature of 16—22°C. After incubation the barley was grown in a greenhouse or an opensided greenhouse. The barley in the field experi- ment was sprayed late in the evening when the natural relative humidity was high. Three to twelve barley cultivars were in- oculated simultaneously at 2 to 5 different stages of growth to determine the effect of the developmental stage of the crops on their response to air-borne infection. In pot ex- periments the first spraying was always done just before the time of heading, the second at early heading stage and the rest at 5 to 10-day intervals after that. In the field barley was sprayed with the spore suspension either a week before or two weeks after heading. Five fungus isolates were studied for differ- ences in symptom appearance and severity. Foliar symptoms were observed and record- ed in all experiments 7 days after treatment. The leaf area showing lesions or total de- struction was estimated using a key publish- ed by Brönnimann (1968) to estimate foliar disease caused by Septoria nodorum Berk. Symptoms were observed, however, until the full ripening of the grain. Harvested grain yields were drained and weighed and samples from them were analyzed for the incidence 98 3 and localization of B. sorokiniana in the seeds as described by Kurppa (1984). Sam- ples of grain yields from the field experiment were also analyzed for germination of the seeds. To test the significance of the data, anal- ysis of variances and t-test were used. Results Foliar symptom incidence and severity due to secondary infection of Bipolaris soroki- niana varied depending on the fungus isolate and barley cultivar. One isolate induced dark brown oval discrete spots while the others also caused leaf blotch, typical of the fungus (Fig. 3). In these preliminary studies, cv. Table 1. Leaf area damagedby Bipolaris sorokiniana. Fungus isolate Barley cultivar Karri Paavo Pomo Mean A 1 17.5* 10.0 10.0 12.5 B 37.5 37.5 37.5 37.5 C 17.5 62.5 25.0 35.0 D 50.0 75.0 50.0 58.3 E 25.0 37.5 25.0 29.2 For fungus isolate see text Per cent damaged leaf area as recorded 7 days after spraying the young non-heading barley with fungal suspension F-values: Fungus isolates = 7.1x , LSDtOO5 = 12.3 % Cultivars 4.7 X = 14.1 % Paavo was found to be extremely susceptible to secondary infection (Table 1.). The fun- gus was capable of causing severe foliar in- Table 2. The effect of crop developmental stage on destroyed leaf area and grain yield in different barley cultivars, due to infection by Bipolaris sorokiniana applied at various intervals. Cultivar Time of spraying I 1 II 111 Mean w/o control DLA* Y DLA Y DLA Y DLA Y Eero Etu Hja-673 Ingrid Karri Otra Paavo Porno Pirkka Suvi Tammi Teemu I = c. one week before heading II = 10 days after I 111 = 20 days after I *DLA = % destroyed leaf area, recorded 7 days after the barley was sprayed with fungal suspension Y = relative grain yield Fungal isolate used was 7550. After spraying the barley was grown in an open-sided glasshouse. Controls for each cultivar were 0.0 (destroyed leaf area) or 100.0 (relative grain yield). F-values: Grain yield/treatment = 186.2", LSD,„„< = 3.8 % —» /cultivar = 15.2", = 9.5 % T-vaUies for treatment/yield: Control 1 = 12.4" Control 11 = 5.6* Control 111 = 7.6' I 11 = 3.5» I 111 = 4.4» II 111 = 0.6 30 59.0 20 80.2 10 75.6 20 76.3 10 73.3 10 81.0 40 64.0 20 69.2 15 72.4 27 64.9 25 78.2 20 56.6 37 84.1 30 84.6 27 78.7 32 95.0 22 80.6 22 96.0 42 68.7 37 72.2 27 88.1 35 81.9 30 84.3 37 81.8 42 93.2 42 89.1 32 83.7 37 89.3 27 79.9 27 92.4 47 88.2 42 72.8 37 92.3 40 80.3 42 84.0 40 74.7 36.3 78.8 30.7 85.2 23.0 79.3 29.7 86.9 19.7 77.9 19.7 89.8 43.0 73.6 33.0 71.4 26.3 84.3 34.0 75.7 32.3 82.2 32.3 71.0 99 fection even at the seedling stage if inocula- tion was followed by incubation of the seed- lings 48 hours at 20° C and 90—100 °/o rela- tive humidity. In greenhouse experiments barley develop- mental stage during infection was of great importance in disease severity and yield los- ses. Infection before heading or directly after it usually resulted in a lower percentage of foliar damage than if it occurred at a later stage (Table 2). Yield losses however, could be relatively high, even if not much assimili- tive leaf area was lost (Fig. 1, Table 2). Sec- ondary infection close to ripening had a less negative effect on the yield than earlier infec- tions had; this was particularly true with ear- ly six-row cvs. Eero, Otra and Paavo. Late foliar infection still caused an average yield reduction of 15 per cent. The highest average yield reductions due to secondary infection were recorded with the cvs. Teemu (29.0 %), Pomo (28.6 %) and Paavo (26.4 %) and the lowest with the cvs. Otra (10.2 %) and Ingrid (13.1 %). Individual results varied with dif- ferent developmental stages of barley, how- ever (Table 2). Inoculation of the crop before heading never resulted in a significantly high rate of infection of the grains in greenhouse experi- ments. (Fig. 2, Table 3). Spraying with the spore suspension at later developmental stages caused increasing incidences of seed infection. The highest per centage of infected seeds occurred when the crop was sprayed at the ripening stage. Infection at the embryos or inner cell layers in the seeds reached its highest occurrence shortly before the maxi- mal incidence of seed infection (Fig. 2). Dra- matic differences were found between the cultivars with respect to the incidence of seed infection and fungal invasion at the em- bryos. The highest rate of seed and embryo infection was found with the cvs. Teemu, Paavo, Suvi, Etu and Tammi, and the lowest with cvs. Ingrid, Otra and Pirkka. Seeds of cv. Karri were not frequently infected but fungal invasion in the embryo of the seeds Fig. I. The effect of barley developmental stage and cultivar on the yield losses caused by Bipolaris sorokiniana sprayed onto the crop in green- house experiments. Fungus isolate A was used. Time of inoculation: 1 = seedling stage, 2 = heading, 3—5 = five day-intervals after heading. F-value: Time of inoculation = 18.4", LSDoos = 8.5 %. Fig. 2. The effect of barley developmental stage and cultivar on the incidence and severity of infec- tion in grain yields caused by Bipolaris soroki- niana sprayed onto the crop in greenhouse ex- periments. For fungus isolate and inoculations see Fig. 1. F-values: Grain infection, time of inoculation = 62.0XX , LSD00J = 8.5 %, culti- var = 17.1“, LSD 005 = 10.0 %. Embryo in- fection, time of inoculation = 257.6“, LSDoos = 3.6 %, cultivar = 27.6", LSDoos = 7.9 %. 100 Table 3. The effect of developmental stage of different barley cultivars on the infection incidence of its grains and embryos due to Bipolaris sorokiniana applied at various intervals. Cultivar Time of spraying I 1 Il 11l Mean IG* IE IG IE IG IE IG IE Eero Etu Hja-673 Ingrid Karri Olra Paavo Pomo Pirkka Suvi Tammi Teemu 7.00.0 0.70.0 2.70.0 2.00.0 3.30.0 1.00.0 2.70.0 0.70.0 1.30.0 0.70.0 4.00.0 6.00.0 9.01.0 18.72.0 8.01.0 4.70.0 4.70.0 2.70.0 19.34.0 10.32.0 6.01.0 12.02.0 15.33.0 24.04.0 Mean 2.70.0 11.11.7 52.822.7 1 I = c. one week before heading *IG = infection incidence of the grains II = 10 days after I IE = infection incidence of the embryIE = infection incidence of the embryos 111 = 20 days after 1 For details see table 2. F-values: Infection incidence (w/o controls) /treatments = 289.7*\ LSD, OOS = 2.5 % —» /cultivars = 41.9X\ = 4.3 % Infection incidence of the embryos/cultivars = 29.2" = 4.4 % (111 only) Fig. 3. Leaf symptoms caused by different isolates of Bipolaris sorokiniana in barley cultivar Paavo as observed 7 days after inoculation. Left to right; control and isolates A E. Fig. 4. Leaf spots and blotches caused by Bipolaris so- rokiniana in a field experiments on barley cv. Pomo. On the left the symptoms as observed one week and on the right four weeks after in- oculation. 52.3 14.0 76.0 27.0 4.7 16.0 26.7 7.0 32.0 9.0 30.7 15.0 70.0 44.0 47.3 21.0 26.0 6.0 78.7 34.0 63.7 34.0 85.3 46.0 22.8 5.0 31.8 9.7 18.5 8.0 11.1 2.3 13.3 5.0 11.5 3.0 30.6 16.0 19.4 7.7 11.1 2.3 30.4 12.0 27.7 12.3 38.4 17.3 101 Table 4. The effect of the developmental stage of dif- ferent barley cultivars on yield reduction due to Bipolaris sorokiniana applied to the field crop. Treatment Cultivar Ingrid Karri Otra Porno Mean Control I' II 100.0* 100.0 100.0 100.0 100.0 76.5 72.2 97.8 96.0 85.6 85.7 95.2 86.0 94.0 90.2 Mean w/o control 81.1 83.7 91.9 95.0 I = Sprayed c. one week before heading II = Sprayed three weeks later Relative grain yield was more severe than average (Fig. 2, Table 3). Some seed infection also occurred due to fungal growth and subsequent spore libera- tion from lower diseased leaves in the open- sided glasshouse, but no invasion of the em- bryos was found. In the field, spraying of the spore suspen- sion on barley also resulted in a high inci- dence of foliar disease at the seedling stage. The fungus caused numerous leaf spots and blotches on all barley cultivars used in the ex- periment. The lesions grew rapidly larger, and natural sporulation was observed seven to ten days after spraying (Fig. 4). Similar leaf spot and blotch development followed a spraying treatment carried out three weeks later, and within one month no visible dif- ferences could be observed between the dif- ferentially treated plants. In addition to spotted and complitely damaged leaves, the fungus also affected the heads and remaining shoots resulting in increased lodging in the treated blocks. Both inoculations significant- ly decreased the grain yields of all barley cul- tivars studied, with the early spraying treat- ment having a greater effect (Table 4). In this experiment the highest yield losses occurred with two-row cultivars Ingrid and Karri, which were previously found to be relatively resistant in greenhouse experiments. A low incidence of disease occurred in control blocks due to natural secondary in- fection by the fungus; however both spray- ing treatments resulted in a great increase of seed and embryo infection over the control (Table 5). The two treatments caused a rela- tively similar seed infection level, but em- bryo infection was much higher with later spraying than with earlier. Cultivar Karri showed higher susceptibility to fungal inva- sion in the embryos than did the other culti- vars. Discussion The importance of Bipolaris sorokiniana as a foliar pathogen of barley is probably greater in North-Western Europe and Easter Canada than anywhere else. The high inci- Table 5. The effect of the developmental stage of different barley cultivars on the infection incidence of its grain and embryos due to Bipolaris sorokiniana applied to the crop in a field experiment. Infection incidence of the grains (Vo) Infection incidence of the embryos (%) Treatment Cultivar Cultivar Ingrid Karri Otra Pomo Mean Ingrid Karri Otra Porno Mean Control I 1 II 9.3 14.0 10.0 9.5 10.7 55.7 83.5 55.3 58.7 63.8 63.2 84.3 78.3 66.7 73.1 0.5 2.0 1.5 0.5 1.3 10.5 16.5 2.5 9.5 9.8 16.0 35.5 16.5 16.0 21.0 I = Sprayed c. one week before heading II = Sprayed three weeks after I Fungal isolate used was A. F-values: Infection incidence of the grains /treatment = 819.2", LSD,OOS = 4.0% —»— /cultivar = 22.3", =4.1% Infection incidence of the embryos/treatment = 274.0", = 2.1 % —» /cultivar = 19.3", = 5.6