TWO CEREAL VIRUS DISEASES IN FINLAND Katri Ikäheimo Agricultural Research Centre, Department of Plant Pathology, Tikkurila Received February 2, 1960 In several districts in Finland damage to oats and other spring cereals has been discovered at various times, and various views have been expressed as to the cause of the damage. It has been observed that the extensive damage to oats in the western coastal region is associated with the occurrence of the leafhopper Calligypona pellucida Fabr. (4). It is assumed that the leafhopper distributes a virus (2), although this has not been proved by experiments. Another view is that the damage is phytotoxaemia caused by the saliva of the leafhopper (6). In the region of Mikkeli in Savo, as well as in southern Ostrobottnia and in Satakunta, Jamalainen (3) found in the summer 1956 a disease in oats which in its symptoms was like cereal yellow dwarf. A disease in oats similar to that found in Finnish western coastal regions has also been found in Sweden. Lindsten (5) has established three cereal virus diseases there. Two are spread by the leafhopper C. pellucida. One disease resembles European wheat striate mosaic and the other is propably a new virus disease. The third virus disease which is transmitted by the aphids Rhopalosiphon padi L. and Macrosiphum granarium Kirby resembles cereal yellow dwarf (5). A disease characterized by excessive tillering in oats and which is spread by the leafhopper C. pellucida has also been observed in Czechoslovakia (8). The bird cherry aphid (Rhopalosiphon padi L.) occurred in exceptionally great quantities in Finland last summer. Plants attacked by these aphids resembled plants infected by barley yellow dwarf (= cereal yellow dwarf). It is known that this disease is transmitted by the bird cherry aphid (12), and in Finland the disease has been found previously in rye grass (9). Thus it was important to study whether the disease found in Finland last summer in oats was a virus disease transmitted by the bird cherry aphid. Experiments were also made with the leafhopper C. pellucida in order to- find out if it transmits viruses also in this country. https://www.c-info.fi/en/info/?token=_jRorofEJT1PVbT0.guKnE7oqbF4MQ4ruS1ojxQ.UOpQlmxc8k7bwFSAPoHdEVR_EocruIVTsfGO6d5FmGwHpN2s0sgHo5Q8i6Gf4H1XmBPoudAwfuy09k1gddAPFnttkQsYoVkl8nTPIXNUxhrsX7iwMj-fpWRjSWWv4o-URHnOgfSDPz7rOCZij_MNwbG27esd_XsRROQ6-HWQYkz8 63 Materials and methods In order to determine the virus diseases, infected plants and vector insects were collected from Uusimaa, South Finland, where bird cherry aphids (Rhopalo- siphon padi) attacked oats severely and from Peräseinäjoki and Laihia in West- Finland, where the disease associated with the occurrence of the leafhopper (Galli- gypona pellucida) has been found in oats. Diseased plants infected by the bird cherry aphids were collected from four districts in Uusimaa for preparing infection feed. Two or three plants which exhibited very clear symptoms were selected from the samples taken from each district. The leaf or half a leaf of the infected plant was placed in a test tube on moist filter paper, and the aphids were transfrred to the leaf with a hair brush. The aphids in the first transmissions from samples collected from Helsinki and Tikkurila were allowed to feed on the infected leaves for periods of 24 or 48 hours. After the infection feed the aphids were transferred to healthy plants, s—lo5—10 aphids on each plant. In two experiments barley was infected; in the other experiments oats were used. Plants to be inoculated were in the I—2 leaf stage. Two days after inoculation the aphids were removed with insecticide sprays. The infected plants were kept in a glasshouse for observation and were sprayed with insecticide once a week. Leafhoppers were collected from fields at Laihia and Peräseinäjoki, West- Finland in the summers 1958 and 1959. In 1959 leafhoppers were collected also from Tikkurila, South Finland. The leafhoppers were mainly adults or nymphs of the last stage. They were reared on winter wheat and barley grown in pots contain- ing 10—12 plants. The leafhoppers were confined on the seedlings with celluloid cages. The upper end of the cage and the two »ventilation» holes on the sides were covered with thin cotton cloth. The open base was pressed into the soil. Small celluloid tubes were used to confine individual leafhoppers on single plants. The cages as well as the plants were labelled with numbers for identifying the insect. Transferring the kafhoppers from the plants was accomplished by means of a suction apparatus. The leafhoppers originating in different localities were kept in their own separate groups. Some leafhoppers at the nymphal stages from each group were reared singly. After their emergence the adults were mated, and each couple was placed n a single cage. The couples, as well as the large colonies, were transferred each week to new plants which were kept in the glasshouse for obser- vation. The progery of each couple was collected immediately after hatching and formed into a separate group. Leafhoppers which themselves as well as their parents had not caused disease were chosen for the transmission tests. For later transmission tests it was possible to use leafhoppers whose parents’ infection ability was known for several genera- tions. For each experiment the progeny of one mother was used; half of them were given the infection feed, while the other half were control insects. Plants infected by leafhoppers in ;he field were used for the infection feeds; the feeding continued from 3 to 10 days generally. In most tests the infection feed was given to half- grown nymphs. The leafhoppers were subsequently transferred to new plants, one leafhopper per plant once a week during approximately one month. The infected plants were kept in a glasshouse and sprayed once a week with insecticide. Results Transmission tests with Rhopalosiphon pad i. The inoculated plants exhibited the first symptoms 14—25 days after the removal of the aphids. The tips of the youngest leaves showed, especially when viewed against light, yellow- green blotches and pale roundish spots. Somewhat later the leaf tips began to turn yellow. The colouring gradually spread from the tips downwards, and the colour of the leaves turned from yellow to reddish yellow, often also bright red or brownish red (Fig. 1). The tips of the leaves curled up. Serrations of the margins could often be seen in young leaves already before the colour changes (Fig. 4). At the stage when only the tips were yellow, the leaves were thick and stiff. The leaves of barley did not exhibid other changes in colouring than yellowing beginning at the tips and spreading finally over the entire leaf. The plants became stunted and some Fig. 1. Oats leaves infected by cereal yellow dwarf. On the right a healthy leaf. Fig. 2, Three oats plants infected by cereal yellow dwarf one month after inoculation. On the right a healthy plant. 64 65 developed abundant tillers (Fig. 2). Panicle emergence was retarded and the florests in the panicles were often blasted. The control plants remained healthy in all the experiments as did the plants on which the aphids were allowed to breed. Under the same external conditions the symptoms appeared similar after each inoculation. In conditions of low-temperature and low light intensity the symptoms were delayed and the amount of discoloration was less than in plants grown under conditions of high temperature and high light intensity. Isolations of plants col- lected from different localities varied only slightly in their symptoms. Transmission iests with bird cherry aphids are presented in the following table. The sources of infection in experiments I consisted of diseased plants collected from fields, while plants infected in the transmission tests from this original material were used for the infection feed in experiments 11, and so on. The transmissions were carried out at 4—5 week intervals. In addition to the experiments listed in the table, succesfa transfers were also made on barley collected at Inkoo, Vestan- kvarn. In continued transmissions it was found that the causal agent of the disease remained easily transferable. Helsinki Helsinki, parish Inkoo Snappertuna Tali estate Tikkurila Vestankvarn Raseborg Control No. of pla:its No. of plants No. of plants No. of plants No. of plants g A 0‘55 'O 'O 'V > 2 a> h 1* a> > n» C ti T 3 "O 'O ti'O'Oü'Oß V J* CJ JS O 4) Vh CO 4) e s ti s tS-v? 3 ts vs 3 -8-5 -s *l3 s Rv9a o jl 8 Jä 8 j| 8 h .S .3 .9 .9 .9 .9 .9 .3 .3 ’> <« .9 1 20 70.0 29 72.5 24 83.2 12 91.5 20 0 II 67 7e.l 10 100.0 22 45.4 10 100.0 30 0 111 40 62.5 23 78.0 10 70.0 20 0 IV 20 60.0 30 73.3 10 0 Total 147 et .4% 92 77.0 % 56 80.5 % 22 95.8 % 80 0 The disease described above is similar to cereal yellow dwarf in its symptoms and in the length of its incubation period. It has been found that the bird cherry aphid acts as a vector of cereal yellow dwarf in England and in Netherlands (12). Since the disease under investigation is spread by the same vector as cereal yellow dwarf and since ts symptoms and incubation period are similar, the disease was identified as cereal yellow dwarf. Transmission tests with Galligypona pellucid a. Health, experimen- tal plants, on which leafhoppers collected from fields at Laihia and Peräseinäjoki had fed, exhibited disease symptoms 10—21 days or sometimes as much as 40 days after the start offeeding. These symptoms were chlorotic spots and threadlike, broken streaks on the leaves which gradually enlarged and finally caused the leaf to turn completely yellow (Fig.B). The chlorosis was first apparent on the youngest leaves. The infected plants became heavily stunted and some developed abundant side 5 66 shoots. Most plants that had been infected at the seedling stage died within I—2 months after infection. The symptoms were similar both in winter and spring wheat and in barley. Young barley leaves often exhibited serrations. Chlorotic streaks were found also on oats leaves 15—30 days after the infection. These, how- ever, soon disappeared and the leaves as well as the whole stem turned reddish yellow or red. The panicle remained in the sheath, and finally the entire plant shrivelled and died. Since these symptoms greatly resembled those caused by the European wheat striate mosaic virus, transmission tests were made with leafhoppers, which act as a vector for this virus. The transmission tests showed that leafhoppers which had not infected plants in two previous generations, and in some tests in three preceding generations. Fig. 3. Winter wheat leaves infected by European wheat striate mosaic. On the right a healthy leaf. Fig. 4. Serrations on barley leaves. On the right a healthy leaf. 67 transmitted the virus from diseased plants to healthy ones. The control insects which descended from the same mothers did not cause the disease. The leafhoppers became capable of infecting plants 15—21 days or some- times even later after the start of the infection feed, but once the leafhopper became infective, it remained so for almost the rest of its life. Only a part of the progeny of each mother proved capable of transmitting the virus, and the different colonies varied greatly in this respect. In preliminary tests the leafhoppers of some colonies did not transmit the virus at all; in other colonies only about 3—B %of the leafhoppers given infection feed were able to transmit the virus. In one colony about half of the leafhoppers proved to be able to transmit the virus. This variation is typical of many species of leafhoppers which transmit viruses: among the same leafhopper species colonies vary greatly in their virus- transmitting ablity (1, 11,13). The European wheat striate mosaic virus is transmitted from infective females through the eggs to their offspring (10, 13). In the present tests this was not ob- served. This may be due to the fact that for the transmission experiments, leafhopper colonies which were inefficient to transmit the virus had been chozen. According to Watson and Sinha (13) the inefficient colonies do not transmit the virus to their offspring, or, if so, only to a very limited extent. On the other hand, with colonies in which many leafhoppers were able to transmit the virus, precise tests were not made to establish the transmission of the virus, to the offspring. It appeared, however, that in certain cases some leafhoppers had received the virus from their mother. Since the disease described above is spread by the same vector as European wheat striate mosaic and since its symptoms and incubation period are similar, the disease was identified as European wheat striate mosaic. Discussion It appears probable that the European wheat striate mosaic virus, transmitted by Calligypona pellucida, has been partly the cause of the damage to oats in West Finland. The symptoms of this damage and those of this virus disease in their later stages in oats are similar, for example stunting and reddening of the plants and retardation or complete inhibition of the development of the panicle. The extent of European wheat striate mosaic in the country is not known. The aphid-transmitted cereal yellow dwarf disease, whose symptoms are dwarfing, excessive tillering and reddening in oats, was common in Finland in the summer 1959. A similar disease has been observed previously in this country, also in the region of damage to oats in West Finland (3), but no attempt was made then to determine the cause. It seems likely that these virus diseases which to a certain extent resemble one another in their symptoms have been involved as the cause of the damage to oats in West Finland. 68 Summary In many regions in Finland damage to oats and to other spring cereals has been discovered at various times, and various views have been expressed as to the cause of this damage. In order to determine the virus diseases which were thought to take part in this damage, diseased plants and vector insects were collected from South and West Finland. The results of the experiments made with Rhopalosiphon padi L. indicated that it transmits a virus disease. On the basis of its symptoms, incubation time and vector, the disease was identified as cereal yellow dwarf. The results of the experiments made with Calligypona pellucida Fahr, indi- cated that it transmits a virus disease. On the basis of its symptoms, incubation time and vector, the disease was identified as European wheat striate mosaic. Acknowledgements. I am very much obliged to Dr Marion A. Watson for her helpful instruction during the time in 1959 when I studied virus diseases at the Rothamsted Experimental Station in England. I wish to thank Mr O. Heikinheimo, M. Sc. (Agricultural Research Centre, Department of Pest Investigation, Tikkurila, Finland) for identifying Rhopalosiphon padi and Mr M. Raatikainen, M. Sc., of the same Institution, for identifying Calligypona pellucida. REFERENCES (1) Black, L. M. 1943. Genetic variation in the clover leafhopper's ability to transmit potato yellow dwarf virus. Genetics 28: 200 209. (2) Heikinheimo, O. 1957. Über die Wiesenzirpe Delphacodes pellucida Fabr. ein Haferschädling und eventueller Vektor einer Getreidevirose. IV. Int. Pfl. schutzkongr. Hamburg. (3) Jamalainen, E. A. 1957. Virustaudeista ja virustautien kaltaisista kasvitaudeista Suomessa. Summary; On plant virus diseases and viruslike diseases in Finland. Valt. maatal. koe- toim. julk. (Pubi. Finn. Stat. Agr. Res. Board) 158: I—sB. (4) Kanervo, V., Heikinheimo, 0., Raatikainen, M. & Tinnilä, A. 1957. The leafhopper Delpha- codes pellucida (F.) (Horn. Auchenorrhyncha) as the cause and distributor of the damage to oats in Finland. Ibid. 160: 1 56. (5) Lindsten, K. 1959. A preliminary report of virus diseases of cereals in Sweden. Phytopath. Z. 32: 420-428. (6) Nuorteva, P. 1958. On the nature of the injury to plants caused by Calligypona pellucida (F.) (Horn. Areopidae). Ann. ent. fenn. 24: 49 59. (7) Osvald, J. W., and Houston, B. R., 1953. The yellow-dwarf virus disease of cereal crops. Phyto- path. 43: 128-136. (8) Prusa, V.. 1958. Die sterile Verzwergung des Hafers in der Tschechoslowakischen Rebublik, Phytopath. Z. 33: 99 107. 69 (9) Slykhuis, J. T. 19 58. A survey of virus diseases of grasses in Northern Europe. FAO Plant Prot. Bull. 6: 129-134. (10) —& Watson M. A. 1958. Striate mosaic of cereals in Europe and its transmission by Delpha- codes pellucida (Fabr.) Ann. appi. Biol. 46; 542 553. (11) Storey, H. H. 1932. The inheritance by an insect vector of the ability to transmit a plant virus. Proc. Roy Soc. B 112: 46 —6O. (12) Watson, M, A. & Mulligan, T. 1957. Cereal yellow dwarf virus in Great Britain. Plant Path. 6: 12-14. (13) — & Sinha, R. C. 1959. Studies on the transmission of European wheat striate mosaic virus by Delphacodes pellucida. Virology 8: 139—163. SELOSTUS: KAKSI VILJAN VIRUSTAUTIA TODETTU SUOMESSA Katri Ikäheimo Kasvitautien tutkimuslaitos, Maatalouden tutkimuskeskus Monilla paikkakunnilla on kaurassa ja myös muissa kevätviljoissa esiintynyt aika ajoin vioitusta, jonka aiheuttajista on esitetty erilaisia tietoja. Läntisellä rannikkoalueella esiintyneen »kaurantuhon» aiheuttajaksi on todettu viljakaskas Calligypona pellucida Fahr. (4). Mikkelin tienoilla Savossa samoin kuin Etelä-Pohjanmaalla sekä Satakunnassa on Kasvitautien tutkimuslaitoksen toimesta (3) kesällä 1956 todettu kaurassa Cereal yellow dwarf- virustaudin kaltaista tautia. Ruotsissa on esiintynyt kaurassa samankaltaista tautia kuin läntisellä rannikkoalueellamme. Taudin esiintymisalueelta kootusta materiaalista on todettu kolme viljan virustautia, joista kahta levittää viljakaskas. Kolmas on kirvojen levittämä ja muistuttaa Cereal yellow dwarfia. (5). Viime kesänä tuemikirva (Rhopalosiphon padi L.) esiintyi maassamme poikkeuksellisen run- saana. Tuomikirvan saastuttamissa viljapelloissa monet kasvit olivat Cereal yellow dwarfin tartutta- mien kasvien kaltaisia. Kävi siis aiheelliseksi selvittää onko meillä kaurassa viime kesänä esiintynyt tauti virustauti, jota tuomikirva levittää. Kun myös viljakaskaan on arveltu meillä levittävän virus- tautia (2) ja Englannissa (10) sekä Ruotsissa (5) on viljakaskaan todettu toimivan European wheat striate mosaic-viruksen sekä Ruotsissa vielä toisen, mahdollisesti ennestään tuntemattoman viruksen vektorina, otettiin tutkittavaksi myös viljakaskaan aiheuttama tauti. Virustautien määrittämistä varten kerättiin aineistoa sekä Uudeltamaalta että Vaasan läänin alueelta. Sairastuneita kasveja hankittiin tuomikirvojen saastuttamilta pelloilta neljältä paikkakun- nalta Uudeltamaalta. Tuomikirvoja koottiin Tikkurilasta ja viljakaskaita Tikkurilasta, Laihialta ja Peräseinäjoelta. Tuomidrvoista kasvatettiin OswALDin ja HOUSTONin (7) kuvaaman menetelmän mukaisesti jälkeläistö, johon kuuluvat yksilöt eivät olleet virusten kantajia. Tuomikirvoilla suoritetuissa siirrostuskokeissa annettiin kirvojen imeä 1—2 vrk:n ajan sairaita kasveja, minkä jälkeen kirvat siirrettiin terveille kauran oraille 2 vrkrksi. Inokuloituihin kasveihin ilmaantuivat ensimmäiset symptomit 14—25 vrk:n kuluttua kirvojen poistamisen jälkeen siten että kaurojen nuorimpien lehtien kärkiosissa oli kellanvihreää kirjavoitumista. Vähän myöhemmin lehtien kärjet alkoivat kellastu a (kuva 1). Kellastuminen levisi vähitellen kärjestä alkaen yhä alemmas tyveä kohden. Samalla lehtien väri muuttui keltaisesta punakeltaiseksi, punaiseksi tai ruskeanpunaisiksi. Nuoriin lehtiin ilmaantui usein jo ennen värin muutoksia nirhamia (kuva 4). Siinä vaiheessa, jolloin vain lehtien kärkiosat elivät kellastuneet, lehtilavat olivat paksuuntuneet ja jäykät. Ohran lehdissä ei ilmennyt muita värin muutoksia kuin kärjistä alkava ja lopulta yli koko lehtien ulottuva keltaisuus. Kasvien pituuskasvu hidastui ja jotkut kasvit muodostivat runsaasti sivuversoja (kuva 2). Röyhylle tulo viivästyi ja muodostuneissa föyhyissä oli surkastuneita tähkylöitä. Kontrollikasvit, joilla oli pidetty tuomikirvoja, jotka eivät olleet saaneet infektioruokintaa 2 vrk;n ajan, pysyivät täysin terveinä kai- 70 kissa suoritetuissa kokeissa. Näin ollen kirvat siirsivät taudinaiheuttajan sairaista kasveista terveisiin, jotka sairastuivat n. 2 3 viikon pituisen inkubaatioajan kuluttua. Edellä kuvattu tauti on sympto- mien, inkubatioajan ja vektorin perusteella Cereal yellow