Maataloustieteellinen Aikakauskirja Vol. 57: 167—181, 1985 The appearance of soil-borne viruses in Finnish plant nurseries II EEVA TAPIO Department of Plant Pathology, University of Helsinki, Finland Abstract. In the beginning of the 1970’5, the occurrence of soil-borne viruses in 30 Finnish nurseries and experimental fields of garden plants at 3 research stations was mapped. Viruses were isolated on 26.9 % of the 672 plant and soil samples collected. The two most commonly found viruses were tobacco necrosis virus (TNV), 42.5 %, and tobacco rattle virus (TRV), 23.7 %. Tomato black ring virus (TBRV) and raspberry ringspot virus (RRSV) were isolated for the first time in Finland. The abundant occurence of TBRV in 32 samples was due to the abundance of Phlox paniculata samples. RRSV was isolated from only a few samples. The vectors ofall of the above-mentioned viruses were found in many samples. The fungus vector of TNV, Olpidium brassicae, was investigated by examining the roots microscopically. The vector ofTRV, the Trichodorus sp. nematodes, and the vector ofTBRV and RRSV, the Lon- gidorus sp. nematodes, were isolated from soil samples. In addition to the foregoing, tobacco mosaic virus was isolated from 31 samples of 6 nurseries and 2 experimental fields. Viruses were isolated from many weed samples, especially from roots of Senecio vulgaris and Slellaria media. Perennials proved tobe virotic. All of the above mentioned viruses, espe- cially TBRV and TRV, were isolated from Phloxpaniculala;TBRV was also found in an As- lilbe x arendsii sample. Dicentra speclabilis, like Phlox, was commonly infected with TRV. No clear results could be obtained from control experiments. Introduction Until now, only preliminary results have been published of the studies made in the be- ginning of the 1970’s on soil-borne viruses pre- sent in Finnish nurseries (Tapio 1972, 1976). In these, it was found that the fungi-borne to- bacco necrosis virus (TNV) and the tobacco Material and methods rattle virus (TRV) transmitted by Tncho- , , . .. .. Samplingctonrs-nematodes, were quite widespread m se- veral nurseries. During the years 1971—73, more samples were collected from nearly all Index words: soil-borne viruses, plant nurseries of the plant nurseries in Finland, and from some experimental fields. An attempt was also made to find out the effects of fallowing, peat addition, and soil disinfection on the survival of viruses in the soil. The collecting of samples began in autumn 1970, and was continued the following au- 167 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=Oq9_Doe98nBsGlqk._Otakq-jjBpg26z4cXy2kw.I7S4C2XNXaSnY5yrxO9_lb8s5E3yHees8r_iHX6oJK-EFRcdQwyIs-GkEUof2s4_EAJJrau_lJZ697kAks3YimUcZAFv5DSwxKzjAi4k6-TY2nAP_pCplBdmRALw3nc9aPyLrGUkoapoh5tTnH8SojOZ1gF2aRAh 168 Fig. 1. Map showing the geografical position of in- vestigated nurseries (• 1—30) and experimental fields (x A—C). Table 1. Viruses and virus vectors in soil and plant samples collected in 1970—1972 from plant schools and ex- perimental fields. Planlschool No. of Virotic samples Virus isolates Vectors No. Locality soil and plant soil roots total TNV ™V TRV TBRV RRSV °,pi ' Tri * Lon' samples of dium cho ' plants dorus dorus 1 60—61 “S 10 0 2»» 9 314 4 + 3 » » 18 0 4 » » 5 0 5 » » 3 1 1 1 6 » » 6 0 7 » » 25 3 7 10 4 6 + 8 » » 11 0 9 » » 30 2 5 7 1 1 4 1 + 10 » » 18 3 3 6 2 4 11 » SW 14 0 12 » » 4 11 1 13 » » 36 2 3 5 1 2 3 1 + 14 » » 2 0 15 » SC 18 II I + 16 » SE 17 112 I—2l 17 » » 22 1 1 2 2 1 + + 18 61—62“» 40 10 7 17 3675 + + + 19 60—61“SC 53 5 16 21 14 3 4 + + 20 » » 7 3 3 2 1 21 » » 9 11 I 22 61—62“» 33 459 8 3 + 23 » » 46 8 11 19 14 3 3 2 + + + 24 » » 63 11 17 28 13 3 2 10 2 + + 25 » W 9 314 4—ll + 26 » » 6 0 27 62—63°» 15 0 28 » » 14 1 1 1 29»» 9 246 243 + 30 » C 13 1 1 I 568 64 85 149 26.1 % 79 23 32 32 5 Experimental fields A 60—61“ S 40 10 3 13 4 12 + + 8»5W3963 9 3 1 5 + + C 61—62“SE 25 7 3 10 2 7 2 + 104 23 9 32 9 8 17 2 31 % Virus isolates in all 88 31 49 32 7 total 207 Virus isolates % 42.5 15.0 23.7 15.5 3.4 tumn and supplemented to some extent during the following two years. Altogether, soil and plant samples were taken from 30 nurseries and from experimental fields for garden plants at three research stations. (Fig. 1 and Table 1.) The soil samples were drilled mainly from the surface soil layer to a depth of 25 to 30 cm, in some cases deeper, about 10drillholes/ sample. In addition, samples of weeds and pe- rennial plants were taken. Virus testing Testing for viruses was done in the same manner as in the preliminary investigations (Tapio 1972). Chenopodium quinoa- and Nicotiana tabacum var. Samsun-seedlings were used as test plants in the first phase, and the latteralso as a bait plant in testing the soil samples. When the reaction was positive, in- oculation were made from these to the in- 169 dicator plants presented in Table 2. The test results were varified with serologi- cal tests and electron microscope. In the se- rological tests, antisera were used which were kindly provided by the following researchers: The source of antisera AS for different viruses and their titers Denmark, Lyngby 4x + Dr. M. Christensen 4x + 64 DDR, Aschersleben + + + + Dr. D. Spaar + + + Scotland, SHRI 1024 Dr. A.F. Murant 2046 The Netherlands, IPO 2048 Dr D.Z. Maat 256 2048 2048 2048 512 1024 1024 4096 The Netherlands 1024 Lisse Made by the author 2048 512 256 256 When preparing our antisera, the viruses were purified using the chloroformbuthanol method (Steere 1956, Tapio 1972). The basic inoculation program for the rabbits consisted of four injections into the vein and two into muscle. The most common test method was micro-precipitation. In addition, the double agar-gel diffusion method was used for testing spherical viruses. Electron microscopy was carried out with a Jeol 100 S. The preparates were usually made by dip method, and to a lesser extent by the spraying method, for securing the TMV- and/or TRV-infection. In addition, virotic tissues were fixed, embedded with polymerizing resins and sectioned ultrathin for electron microscopy. Vector studies The Olpidium-investigations were made as in the preliminary studies (Tapio 1972): exa- mining microscopically, soaking the washed roots 15—20minutes in water in a Petri dish, and watering seedlings with zoospore suspen- sion, either including TNV-suspension or not. The nematode samples were extracted with the Seinhorst-method as in the preliminary ex- Control trials periments. The amounts of soil used for soaking were 100 g or 150 g for mineral soils, and 200 g for peat soils. Marja-Leena Mag- nusson (nee Sarakoski) identified the nema- todes by genus. Part of the extracted nema- TNV TRY TBRV RRSV AMY SLRV CLRV TobRSV TomRSV 256 512 2048 1024 512 2048 1024 todes were immediately transferred to the roots of healthy Samsum-tobacco seedlings grown in steamed soil. Two weeks later, the test plants were inoculated with sap from the tobacco roots. Tests of weeds and perennial plants In addition to isolating viruses from weed and perennial plant samples, the suspectibili- ty of the most common weeds and some or- namental plants to viruses was tested by inoc- ulating them artificially. The plants, mostly seedlings, were inoculated mechanically and/ or using vectors with a chosen isolate of every investigated virus. After two to three weeks, reinoculations were made from different parts of the experimental plants to indicator plants. In control experiments, an attempt was made to determine the effects of fallowing, peat addition, (commonly used in nurseries), and chemical disinfection on the occurrence of nematodes and viruses. In the experimen- tal plots, the nematode populations were small and unevenly distributed. 170 3 One trial was organized in plant nursery no. 24 at Pälkäne, where Longidorus- nematode was isolated from soil samples and tomato black ring virus (TBRV) from 7 of 22 Phlox paniculata-\arieties. The soil quality was un- even, varying from predominantly clay-silt to predominantly sand. The nematodes occurred most densely in a spherical area in the middle of the experimental area. The size of the ex- perimental plots was 4 X 8 m. In experiment A, there were only two replicates, while in ex- periment B, there were three. The latter was on a block fallowed for one year beforehand, and situated next to A. In autumn of the first year of the experiment, a 4 m wide strip 2 m from the end of each experimental plot was separated from the middle of experiment area A and harrowed thoroughly. Di-Trapex (dichlorpropan-dichlorprop + methylisothio- syanat) was injected (500 1/ha) by the supplier company (Huhtamäki/Fincos) on the 20th September in 1973. The soil temperature was + B.3°C. The treated soil was rolled. Soil and plant samples were taken from all of the plots four times in summer 1983, and the following year in June and September, to test nematodes and viruses. From each plot, 49 samples were taken, first removing 5 cm of the surface soil with a drill 2.5 cm in diameter and 25 cm in depth. The drill was cleaned with water and alcohol after being used on each plot. The results are shown with the equivalent number of extracted nematodes per 200 g of soil. A similar experiment was set up on the sandy experimental ground of the Agricultural Research Center at Tikkurila, where Tricho- dorus-nematode and tobacco rattle virus (TRY) had been found. The size of the plots was 2x4 m and there were three replicates. In the first year of the trial, the effects of fal- lowing and peat addition on the incidence of nematodes and TRY was comparad using a plant stand consisting of perennials such as Anemone, Liatris, Delphinium, Viola, as well as certain ornamental shrubs. The experiment area was expanded the next year by mixing granulated Nemagon (1, 2-dibromi-3-chlor- propan) 700 kg/ha into half of the new plots on the 20th of May, 1974. The test plant po- tato cv. Sieglind was planted two weeks after Table 2. The reaction of test plants infected with isolated viruses and some of their characteristics. Test plant Viruses/number of isolates tested Symptoms in test plants +L = local lesions 1, +S = systemic l TNV/5 TMV/3 TRV/5 TBRV/2 RRSV/1 Chenopodium amaranti- +L +L ±S+L—+L +S +L color C.&R. (irreg.) C. guinea Willd. +L +L ±S +L —+L+S+L +S Nicotiana glutinosa L. ±L +L —+L±S— N. tabacum L. cv. Samsun +L ±L +S +L +S ±L ±S cv. White Burley +L +S +L +S Petunia hybrida L. ±L ±L ±S ±L ±S +L +S +L +S Phaseolus vulgaris L. +L +L —±L±L±S ±L ±S Telragonia expansa L. + L +L +S ±L ±S 1± L and ± S reaction variable with isolates, no reaction Size of the particles, nm ca. 26 300 180—200x22 30 30 40—120x22 Thermal inactivation point 80—95°C 80—90°C 70—75—80—85°C 60—65°C 65—70°C Stability in vitro weeks 2—6 >2O 6—B 2—3 2—3 Dilution end point 10-4—lo-5 10~6 —lo~7 10-"—10-6 10-3 —lo-4 10-3—lo-4 171 the treatment. The samples were taken the same way as in the previously described ex- periment. In both experimental areas, Tagetes erecta L. was planted on 2 m 2 plots, because the excretion of the roots of this plant is found to have nematicidal effect (OoeStenbrink et al. 1957 and Uhlen-Broek and Buloo 1958). Results The occurrence of viruses and vectors in nurseries and experimental fields On the 30 investigated nurseries (Fig. 1.), 21, or 70 %, were found to have soil-borne viruses. Viruses were isolated in 149, or 26.2 °/o, of the 568 plant and soil samples (Table 1). Of the 104 soil and plant samples collected at the three experimental fields of garden plants, 32, or 31 %, were found to contain viruses. Almost half, 42.5 °7o, of all virus isolated were of tobacco necrosis virus, TNV, which was present in nearly all nurseries. The vector in TNV, Olpidium brassicae, was found in the samples of 12 nurseries by examining micro- scopically either the roots of sample plants, or the roots of tobacco or lettuce which were grown as bait plants on soil samples. How- ever, not all of the samples were investigated methodically in this respect. Tobacco mosaic virus, TMV, was found in 31 samples, which were from six nurseries and two experimental fields. One rather small nur- sery, no. 7, was so heavily infected with TMV that the grower found it difficult to grow healthy plants without the yearly addition of peatcover. Tobacco rattle virus, TRY was isolated from 49 samples of 13 nurseries and two ex- perimental fields. Trichodorus-nematode was soaked from two soil samples of each four nurseries and two experimental fields, the amount of nematodes varying from 10 to 49 in 100 g soil. Tomato black ring virus, TBRV, was found commonly in 32 samples of 9 nurseries. TBRV was most often isolated from the roots of Phlox paniculata or from weeds at the site, or from the soil. Longidorus-nematode was soaked from the soil samples collected on four sampling sites, the amount varying from 11 to 35 in 100 g soil. Raspberry ring spot virus, RRSV, was iso- lated from the roots of Senecio vulgaris once, from Phlox paniculata twice, and from Ribes rubrum cv. Rondom once. TNV, TMV and TRY were isolated equal- ly from both plant and soil samples, while TBRV and RRSV were isolated almost exlu- sively from the roots of perennial plants. Isolated viruses Altogether, 207 virus isolates were made (Table 1). A summary of the local (L) and Fig. 2. Tomato black ring virus. Local lesions and sys- temic symptoms in Chenopodium quinoa. 172 173 systemic (S) symptoms of the various viruses on the most important test plants is presented in Table 2. When symptoms were unclear, in- oculations back to sensitive test plants ex- hibiting distinct reactions were made from ex- perimental plants, in order to detect latent in- fections. In most cases the results were checked serologically, or by electron micro- scope. TNV- and TRV-isolates were similar to those described earlier (Tapio 1972), that is some test plants, especially Nicotiana-spedes and Phaseolus vulgaris, reacted to some ex- tent in a variable manner when inoculated with isolates. The determination of TNV was confirmed serologically, primarily by using a selfmade mixture of antisera of serotypes A and D. (cf. Tapio 1972). Comparative tests were also made with other antisera. Aside from the use of test plants and sero- logical reactions, the determination of TRV- isolates was confirmed most often with elec- tron microscope. The determination of TMV did not cause problems. Tomato black ring virus, TBRV and rasp- berry ring spot virus, RRSV were first identi- fied with Chenopodium-spedes. The former caused systemic symptoms on both C. quinoa and C. amaranticolor, the latter only on C. quinoa (Fig. 2). Petunia reacted variably, only seldom with clear ring spot symptoms (Fig. 3 and 4). The determination of TBRV and RRSV was always confirmed serologically. In the material treated here, there was no arabis mosaic virus, AMV, which was later found in rhubarb (Tapio unpublished). Thermal end points varied considerably, es- pecially in TNV-, TMV- and TRV-isolates. Stability in vitro and dilution end point were normal for the viruses (Table 2). Other detailed studies with different isolates could not be made because the author moved, while the handling of the material was unfinished, from the Agricultural Research Center to the De- partment of Plant Pathology of Helsinki Uni- versity, which at that time had no virus re- search equipment. The effect of soil type on the occurrence of different virus species Fine sand and silt were the most common soil types in different plant nurseries (Fig. 5). About one fifth of the samples were soils which were primarily or solely organic mat- ter. Clay soils were also fairly common, but sand was rare. Viruses were isolated from 28 °/o of the mineral soil samples and about half of the peat and mull samples. TNV, the one that ap- peared most commonly, was most often found in fine sand and peat soils, TMV in clay and mull soils. Among the nematode-transmitted viruses, TRV was most common in sand and fine sand soils, and TBRV on silt soils, and on soils lighter than silt. Fig. 3. Tomato black ring virus. Systemic interveinal chlorosis in Petunia hybrida. Fig. 4. Raspberry ring spot virus. Systemic ring-spotting in Petunia hybrida. Susceptibility of weeds and some ornamental plants Soil-borne viruses were isolated from half of the samples of 16 weed species (Table 3). Senecio vulgaris and Stellaria media were the most common virotic weeds. In infection ex- periments, all the studied 22 weed species proved to be susceptible to two or more of the viruses tested, either with clear symptoms or latent infection wich was confirmed withback inoculation to indicator plants (Table 4). The examined TNV-, TMV-, TRV-, TBRV- and RRSV-isolates infected the following weed species that commonly occur in nur- series, either by mechanical inoculation or through infection by soil-borne vectors: Achillea millefolium, Capsella bursa-past oris, Lamium hybridum, L.purpureum, Ranun- culus acris, Rumex acetosella, R.crispus, Senecio vulgaris, Stellaria media (Fig. 6), Trip- leurospermum maritinum and Viola arvensis. Ranunculus repens was found to be infected with all but TMV, and Urtica urens with all but RRSV. The other test subjects shown in table 4 were less susceptible than the above- mentioned species. One third of 101 Phloxpaniculata- samples was found virotic (Table 3). The Phlox ma- terial of the nurseries in Finland is badly in- fected with viruses, especially with TBRV (Fig. 7), but also withTRV, TNV and RRSV. Dicentra spectabilis was commonly infected with TRV. This virus was isolated from all eight D.spectabilis-examples collected from seven plant shops. Furthermore, it is suscep- tible to TMV (Table 5). From the Astilbe hybrida-sample, TBRV and TNV were iso- lated. Susceptibility tests were made for some or- namental plants (table 5). Because there were difficulties in obtaining suitable experimental plants, sample plants with naturally-occuring viral infection have also been shown in the table. Where infection was found in the roots Fig 5. Occurrence of viruses in different soil types in 1970—1972 174 of such plants, it is indicated in the tables by the annotated letter ”R”. Tagetes erecta, which exhibits clear symp- toms with TNV, TMV, and TRV, was used as a test plant for annuals as well as peren- nials. All the above-mentioned viruses were also isolated from theroots of Tagetes. TRV and TBRV on the other hand, could not be isolated from the roots of Tagetes growing in the experimental areas. Control experiments The small-scale experiments, in which an effort was made to determine the effects of fallowing, peat addition and chemical disin- fection of soil on the persistence of nematodes and viruses in the soil, did not lead to any clear results. In the beginning of the experiment the nematodes were spread unevenly through the experimental area. Longidorus- nematodes Table 3. Occurrence of viruses in roots of different plant samples in 1970—1972. Plant samples No. of plant No. of virotic Plant samples with viruses samples samples plant "rov TMV TRV TBRV RRSVcollected collected samples llvlv IKV IBKV KKiv Total Total Weeds: Brassica rapa L. 1 0 Capsella bursa-pasloris (L.) Med. 3 0 Centaurea cyanus L. 1 0 Chenopodium album L. 2 0 Elymus repens (L.) Gould. 2 0 Lamium sp. L. 5 2 11 Matricaria inodora L. 2 0 Planlago major L. 1 I I Rorippa paiustris (L.) Besser 4 1 1 Rumex acetosella L. 1 1 1 Senecio vulgaris L. 45 15 11 1 1 1 1 Sonchus arvensis L. 2 0 Sperguia arvensis L. 1 0 Slellaria media (L.) Vili. 133 14 8 3 4 2 Taraxacum officinales Web. 48 5 3 1 1 Urtica urens L. 2 0 Viola arvensis Murray 21 6 5 1 Perennial plants: Aslilbe hybrida 1 1 1 Crocus vernus L. 1 I 1 Dicentra spectabUis (L.) Lem. l( + 8)' U + 8) 1 1(8)' Phlox paniculala L. 101 34 10 1 10 21 2 Viola cornuta L. 4 0 Total number of samples 382 82 38 9 18 27 3 % of virotic samples 21.5 % of virotic isolates 40.0 9.5 18.9 28.4 3.2 1 Collected in 1973 175 Fig. 6. Tobacco necrosis virus. Local lesions in Slellaria media. were concentrated in a circular area, their number varying from 0 to 46/200 gr soil, in different plots. Trichodorus-nematodes were present in the whole experimental area, al- though their number varied from 18 to 84/200 g soil in different plots. The perennial weeds Aegopodium podagraria L. at Pälkäne and Elymus repens L. at Tikkurila made the weeding of fallow plots difficult. Longidorus-nematodes could not be found at all by soaking from the plots after fallows lasting two or one and a half growing seasons. They were, however, found in weedy plots after a fallow lasting one growing season. Nematodes could not be found in soil that had been treated with Di-Trapex (Table 6). In other plots, however, so few nematodes were found, in some replicates that the differences were not significant in all soakings. Both TBRV and TNV viruses were isolated with bait plants from all the plots except those with a 3-year fallow at the end of the experiment. Fallowing and peat addition diminished to some extent, but not significantly, the amount of Trichodorus-nematodes. The effect of Nemagon-treatment was not significant, the number of nematodes being small in all the plots at the end of the experiment. TRV could be isolated with bait plants only from stand plots. Table 4. Reaction of weeds inoculated with Finnish type isolates or naturally infected of soil-borne viruses. Plant species Reaction 1 of weeds infected by TNV TMV TRY TBRV RRSV median. Olpid. mechan. median. Trichod. mechan. Longid. mechan. Achillea millefolium L. SR L LSR L LSR Capsella bursa-pastoris (L.) Med. —R L LS SR LSR SR LSR Chenopodium album L. L R L R Epilobium montanum L. SR L R Erysimum cheiranthioides L. LSN R LS SR Galium spurium L. SR Lamium hybridum Vili. L R LSR LSR SR LSR R LSR L. purpureum L. L R LSR LSR SR LSR R LSR Lapsana communis L. L Matricaria inodora L. R 3 Myosotis arvensis (L.) Hill. R 3 Plantago major L. R R 2 R 3 Polygonum convolvulus L. L S SR R Ranunculus acris L. L LS R 3 R R. repens L. R LS LSR L R Raphanus raphanistrum L. R LS R 3 Rorippa palustris (L.) Bass. R 2 Rumex acetosella L. L R L R 3 LS L R R. crispus L. L R L R LS LSR L Senecio vulgaris L. R L LS R LSR LSR Sonchus arvensis L. R SR Spergula arvensis L. —(S)R R —(S) — R R Stellaria media (L.) Vili. L R L LSR SR LSR LS Taraxacum officinale Web. R R R Thlaspi arvense L. R Tripleurospermum inodorum Sch.Bip.' L L LSR R LS LSR Urtica dioeca L. R R U. urens L. RLS LS RLS Viola arvensis Murr. R LSR LR R LSR 1 L = local lesions, S = sprouts systemic infected, R = roots infected, = no infection 2 weeds grown on TMV infested soil, not mechanically inoculated 3 weeds grown on nematode and virus infested soil, not inoculated 176 The influence of weather on the occurrence of nematodes appeared to be more distinct than that of different treatments. Summer 1973 was dry, and the number of nematodes clearly diminished in the surface layers of the soil temporarily until the autumn rains (Table 7). Discussion Soil-borne viruses were found in 70 % of the nurseries in Finland. From the 568 plant and soil samples collected at 31 nurseries, viruses were isolated from 26.1 %. The most commonly found virus isolates were tobacco necrosis virus, 42.5 %, and tobacco rattle virus, 23.7 %. They are found in almost the same proportions as in Swedish nurseries, ac- cording to Ryden and Eriksson (1978). The vector of TNV, Olpidium brassicae, was found in the samples of 12nurseries. The occurrence of fungi in all samples was, how- ever, not determined, so the frequency of oc- currence in Finland could be greater than 40 °7o. The frequency of fungal occurrence in Table 5. Reaction of ornamental plants naturally infected or inoculated with Finnish isolates of soilborne viruses Plant species Reaction 1 of ornamental plants to soil-borne virus isolates TNV/Mn 31 TMV/ TRV/Mn 159 TBRV/Mn 389 RRSV/ Mn 337 Mn 498 Mn 499 mechan. Olpid. mechan. mechan. Trichod. mechan. Longid. mechan. Anemone pulsatilla L. LS L Aquilegia vulgaris L. LS L(S) L Aruncus dioicus (Walt.) Fern. L —— R Aslilbe D. Don. (A. x arindsii) Begonia L. (B. x horttnsis) LS Bergenia x schmidtii (Regel) Silva-Tarouca LS Dicenlra spectabilis (L.) Lem. LSR— —SR SR Euphorbia cyparis- sias L. L L Lialris spicala (L.) Willd. L L L Phlox paniculala L. LSR SR —SR —SR SR LSR SR Primula x pubescens Jacq. + SR Solidago x hybrida L. R —R R Viola cornula L. R R R Tageles erecta L. annual LS RLSR L— R 1 See table 4 177 Fig. 7. Tomato black ring virus. Local ring spots in Phlox paniculala. Swedish nurseries is 50 %, (Ryden and Eriks- (1980) found TNV, however, later causing son 1978) and in Denmark 75 % (Jacobsen 1943). Proportional to the samples taken, TNV was isolated most commonly from fine sand and silt, as was the case with Ryden and Eriksson (1972). According to Mac Farlane (1968), TNV and its vectors were most com- mon in sandy soils, which are, however, rare in Finnish nurseries. TNV was common in weeds such as Sene- cio vulgaris, Stellaria media. Taraxacum of- ficinale and Viola arvensis. It has been isolated from the roots of numerous plants, but caused systemic infection only in quite few plants (Kassanis 1970). Bremer and Lahdenperä heavily systemic infection in out-door cucum- bers in Finland. Tobacco rattle virus (TRY) was isolated most commonly from light soils, confirming what other researchers have found (Van Hoof 1970, Cooper 1971 and Ryden and Eriksson 1978). TRY commonly infected pe- rennials such as Phlox paniculata and Di- centra spectabilis (cf. Lihnell and Nilsson 1969) and was isolated from certain weeds, for example Stellaria media (cf. Cooper and Harrison 1973). The vector of TRY, Trichodorus sp., was isolated from the soil samples of four nur- series and three experimental fields. The Table 6. Changes in the abundance of Longidorus sp. in untreated, fallowed and chemical treated soil. Treatments Mean number of Longidorus/200 g soil on the Viruses isolated m 1973—1974 10 573 14 673 18 773 16 g73 10 674 2 0. 9. 74 . Wlt h H ba ‘‘ P!fntS in the end of exp. + A. Soil with peren- nial plants in 1972 with crop 7.2 3.8 1.3 0.7 4.0 2.0 + with crop, peat added 4.8 1.2 0 0 1.0 0 + fallowed 11.2 4.0 1.0 0.4 0 0.5 + fallowed, peat added 3.7 0.4 0 0 0 0 + D-D-treated 1 6.7 2.3 0.6 0.3 1 0 0 + B. Soil fallowed in 1972 fallowed onward 0 0 0 0 0 0 weedgrown 6.0 2.3 0.3 0 2.0 0.5 + Di-Trapex treatment 500 1/ha the 20. 9. 1973 (arrow), rolled. Table 7. Changes in the abundance of Trichodorus sp. in untreated, fallowed and chemical treated soil. Treatments Mean number of Trichodorus/ 200 g soil on the Viruses isolated in1973 -* 974 23.5.73 25.6.73 4.8.73 1.9.73 16.6.74 19.9.74 bait plants in the end of exp + with crop 1 31.3 2.3 10.7 30.7 32.0 1.0 + with crop, peat added 23.8 7.0 1.3 28.0 15.0 1.0 + fallowed 23.3 2.0 10.7 29.3 14.0 0.5 fallowed, peat added 19.0 4.7 7.6 24.0 8.0 0 Potato, untreated 7.0 0.5 + Potato, treated2 13.0 0 10. 6. 73 planted; Anemone pulsatilla, Begonia semperftorens, Lialris spicala, Delphinium cullorum, Amelanchier spicata; Cotoneaster integrima, Crataegus intricata, Potemilla fruclicosa, Rosa rugosa 2 Nemagon treatment 0.7 kg/ha the 21.5. 1974 (arrow) 178 soaking of nematodes was not, however, per- earlier described RRSV as the cause for red formed on all the samples, so it is probable that Trichodorus is also present in other ex- perimental sites where TRV was isolated. It has been found to be quite common in Scan- dinavian countries (Kristensen and Engsbro 1966, Björnstad and Stöen 1967). The relative abundance of tomato black ring virus (TBRV) can be explained by the abundance of Phlox paniculata-samp\es. The one-sided sampling can be criticized. RydFn and Eriksson (1978) isolated TBRV only from one nursery sample. Ryden (1965) has, on the other hand, isolated TBRV from Phlox plants as Schmeezer (1963) did before her. The same virus was also isolated from the only Astilbe hybrida-samp\e, as did Schmeezer (1963). The Longidorus-nematodes soaked from four sample sites were not identified by spe- cies. Comparison to Scottish (Taylor and Murant 1969) and Swedish (Andersson 1974 and Eriksson 1975) studies gives cause to as- sume that the species in question is L.elonga- tus. Even a single Longidorus- nematode was able to transmit TBRV to young petunia seed- lings, as Harrison (1969) had demonstrated with L.attentatus species. Raspberry ringspot virus (RRSV) could also be isolated from the roots of Phloxpaniculata two times, once from Senecio vulgaris and once fromred currant, Ribes rubrum cv. Ron- doin. Bremer (1983) has later isolated RRSV from black currant cv. Sunderbyn and Öje- byn in Finland. Van Der Meer (1965) has currant spoon-leaf. The virus was not trans- mitted with Longidorus-nematode in this study. The relatively low occurrence of Longi- ctonzs-nematode, and the relative abundance of the virus it transmits in perennials, gives cause for the assumption that viruses as well as nematodes may have been introduced to Finland with vegetatively propagated plant material. In Sweden, the ten nurseries, from where Eriksson isolated Longidorus-nema- todes (Ryden and Eriksson 1978), are all situated to the south of Finland. Although TNV, TMV and TRV were iso- lated from the roots of inoculated Tagetes erecta, TRV and TBRV could not be isolated from the roots of Tagetes growing on the ex- perimental areas. Tagetes has been found to have nematicidal effect (Ooestenbrink et al. 1957 and Uhlenbroek and Bijloo 1958). It should also be noted that soil-borne vi- ruses were isolated most commonly from old nurseries, particularly in the immediate vicin- ity of office buildings and packing rooms. In such areas where perennials were cultivated, fallowing and rotation was practiced less frequently than on other parcels. Because soil- borne viruses, especially Nepo- and Tobra- viruses, are commonly seedborne in weeds (Lister and Murant 1967), which act as in- termediate hosts for nematodes, it is logical to assume that careful fallowing diminishes their occurrence (Cooper and Harrison 1973, Hanada and Harrison 1977). References Andersson, S. 1974. Skador av Longidorus elongatus i jordgubbar. Växtskyddsnotiser 38: 14—18. Babos, P. and Kassanis, B. 1963 Serological relationship and some properties of tobacco necrosis virus strains. J. Gen, Microbiol. 32: 135—144. Bjornstad, A. and Stoen, M. 1967. Rattlevirus med Trichodorus pachydermus som vektor. Norsk Landbruk 167/8: I—B. Bremer, K. and Lahdenperä, M-L. 1980. A disease of out-door cucumbers by the tobacco necrosis virus in Finland. Ann. Agric. Fenn. 19: s—B. Bremer, K. 1983. Viral diseases occuring in Ribes spe- cies in Finland Ann. Agric. Fenn. 22: 104—109. Cooper, J.I. 1971. The distribution in Scotland of tobac- co rattle virus and its nematode vectors in relation to soil type. PI. Path. 20: 51—58. 179 Cooper, J.I. and Thomas, P.R. 1971. Chemical treat- ment of soil to prevent transmission of tobacco rattle virus to potatoes by Trichodorus spp. Ann. Appi. Biol. 69: 23—34. Enosbro, B. 1973. Undersögelser og forsög vedrörende jordbärne vira. 1 Rattlevirus, fortsatte undersögelser i kartoffler. Tidsskr. Pl.avl 77: 103—117. Eriksson, B. 1974. Virusspridande nematoder. Växt- skyddsnotiser 38: 43—51. Hanada, K. and Harrison, B. 1977. Effects of virus genotype and temperature on seed transmission of nepoviruses. Ann. Appi. Biol. 85: 79—92. Harrison, B. 1969. On the transmission of tomato black ring virus by Longidorus attenuatus (Nematoda). Zentbl. ParasitKde 123; 226—229. Hoof, Van H.A. 1970. Some observations on retention of tobacco rattle virus in nematodes. Neth. J. PI. Path. 76: 329—330. Jacobsen, B. 1943. Studies on Olpidium brassicae (Wor.) Dang, Contr. Dep. PI. Path. R. Vet. Agric. Coll., Copenhagen 24: 1 —53. Kassanis, B. 1970. Tobacco necrosis virus. CMI Descr. Pl. Vir. No. 14. Kristensen, H.R. and Enosbro, B. 1966. Undersögerlser og försög vedrörende jordbärne vira. 1 Rattle-virus. Tidsskr. Pl.avl 70: 353—379. Lihnell, D. and Nilsson, B. 1969. Vorkommen von Tabakrattle-Virus on Dicentra speclabilis in Schweden. Phytopath. Z. 65: I—6.1 —6. Lister, R.M. and Murant, A.F. 1967. Seed-transmission of nematode-borne viruses. Ann. Appi. Biol. 59: 4962. Macfarlane, I. 1968. Transmission of tobacco necrosis virus to higher plants by Olpidium a model for the activities of lower fungi parasitic in algae. Veröff. SELOSTUS Maalevintäisten virusten esiintyminen Suomen taimitarhoissa ja eräillä koekentillä Eeva Tapio Helsingin yliopiston kasvipatologian laitos, 00710 Helsinki Maalevintäisten virusten esiintymistä 30 suomalaises- sa taimitarhassa jakolmen tutkimusaseman puutarhakoe- kentällä selvitettiin 1970-luvun alussa. Kerätyistä 672 kasvi- jamaanäytteestä eristettiin 161 :stä eli 26.9 %:sta viruksia. Yleisimmin esiintyi tupakan nekroosivirusta (TNV) ja tupakan rattlevirusta (TRV), joita oli 42.5 % Inst.-f.-Meeresforsch.-in Bremenhaven.-Sonderdr. 1968 Bd. 3: 133—148. Murant, A.F. and Taylor, C.E. 1965. Treatment of soil with chemicals to prevent transmission of tomato black ring and raspberry ring spot viruses by Longidorus elon- galus (de Man). Ann. Appi. Biol. 55: 227—237. Ooestenbrink, M., Kuiper, K. and S’jacob, J.J. 1957. Tagetes als Fiendpflansen von Pralylenchus-Arten. Nematologica Suppl. 2: 424S —4335. Ryd6n, K. 1965. Phlox ringfläck en svär sjukdom or- sakad av tomat-svartringvirus. Växtskyddsnotiser 29: 77—81. Ryd£n, K. and Eriksson, B. 1978. Jordburna virus och deras vektorer i svenska plantskolor. Växtskyddsrap- porter, Trädgärd 3. Swed. Univ. Agric. Sci, Uppsala 1978. Schmelzer, K. 1963. Untersuchungen an Viren der Zier- und Wildgeholze. 4. Mitteilung. Versuche zur Dif- ferenzierung und Identififerung der Ringfleckenviren. Phytopath. Z. 46: 315—342. Tapio, E. 1972. The appearance of soil-borne viruses in Finnish plant nurseries. Maatal. tiet. Aikak. 44: 83—92. 1976. Taimitarhojen maalevintäiset virukset. Koetoim. ja Käyt. 33: 17—20. Uhlenbroek, J.H. and Bijloo, J.D. 1958. Isolation and structure of a nematicidal principle occuring in Tagetes roots. Proc.lV Int. Cong. Crop Protect. Hamburg, 1957: 579—581. Van Der Meer, F.A. 1965. Investigations of currant viruses in the Netherlands. 11. Futher observations on spoon leaf virus, a soil-borne virus transmitted by the nematode Longidorus elongalus. Neth. J. Plant. Path. 71; 33. Ms received April 1, 1985 ja 23.7 °7o virusisolaateista. Tomaatin mustalaikkuvirus (TBRV) ja vadelman rengaslaikkuvirus (RRSV) eristet- tiin ensi kertaa Suomessa. TBRV’n runsas esiintyminen 32 näytteessä johtuu lähinnä syysleimunäytteiden (Phlox paniculata L.) runsaudesta, RRSV eristettiin vain muu- tamasta näytteestä. Kaikkien edellä mainittujen virusten 180 vektoreita tavattiin useissa maa- ja juurinäytteissä. TNV’n sienivektoria Olpidium brassicae (Wor.) Dang. tutkittiin juuriamikroskopoimalla. Vektoriankeroisia, TRV’tä siir- täviä Trichodorus sp. sekä TBRVtä ja RRSVtä siir- täviä Longidorus sp.-ankeroisia eristettiin maanäytteis- tä huuhtomalla. Edellä mainittujen virusten lisäksi mää- ritettiin kuuden taimitarhan jakahden koekentän 31 näyt- teestä tupakan mosaiikkivirus (TMV), jonkavektoria ei tunneta. Viruksia eristettiin monista rikkakasvinäytteistä, eri- tyisen runsaasti pihatähtimön (Stellaria media (L.)Vill.) japeltovillakon (Senecio vulgaris L.) juurista. Monivuo- tiset ryhmäkasvit olivat yleisesti viroottisia. Syysleimuis- ta eristettiin kaikkia edellä mainittuja viruksia, useimmiten TBRV ja TRV. TBRV tavattiin myös jaloangervossa As- tilbe x arendsii). Särkynytsydän (Dicenlra spectabilis (L.) Lem.) oli kuten syysleimukin yleisesti TRV’n infektoima. Torjuntakokeista ei saatu selkeitä tuloksia. Huolellisen kesannoinnin todettiin kuitenkin selvästi vähentävän vi- rusten ja niiden vektoreiden esiintymistä. 181