THE EFFECT OF POTATO RUGOSE ON THE YIELD OF SOME POTATO VARIETIES Onni Pohjakallio, Laura Karhuvaara and Simo Antila Department of Plant Pathology, University of Helsinki Received January 31, 1961 In field experiments, the tuber yield of potato rugose diseased plants of Fx clones descended from the species hybridization Solanum dernissum x S. tuberosum (Rosafolia) appeared to amount on an average to about 35 % of that of the healthy plants (6). Howerer, it seemed that the strength of the disease manifested itself differently in the clones infected during the different years. Variations which had arisen from bud mutations were observed in this potato material, and thus no answer had been given to the question of whether the variation in the strength of the dis- ease depended on the heterogeneity of the potato material or on that of the virus infecting it. In the following, the study of the effect of the potato rugose on the yield of the potato is based on more uniform potato material. Most of the investi- gations were made with the variety Harbinger; some experiments were also carried out with the varieties Aquila and King George V. In the field experiments proper, which began in 1953, the tubers were set at distances of 1.2 metres (Fig. 1) apart, and the tuberyield of each plant was put into a separate paper bag, in which it was preserved over the winter. Consequently, the tubers of the different potato plants were not mixed together, and furthermore the potato plants did not touch each other either in the field or during storage. Ac- Fig. 1. Field experiments with the virus-diseased Harbinger potato plants. https://www.c-info.fi/en/info/?token=hpi3MydKXbnd7PYL.zbk84wyQRpe0I0Y2sT6Jhw.ij1yRknPYSGK8zzC739MPfxaBZ9BMd_WJDu-56ALZWPkFWA-1N-AIdvyeUr2NVihTp9ewWXEo6wGGVs6X_beS1BUHx_Vso-ReAMyeTDjOEacHBz15682Ld21l2R9jBD2DPe9GorgmqYJAxMhUlI1u7iYjABYLyUzdTbP8SDxE35vK1Hjp-6-o2vqr3QPGI3JHYOFTWl97Tx4PwJYmfCxww 90 cordingly, only vectors could have been the reason for the transmission of the infec- tion; there were plenty of aphids on the potato plants in summertime. In some field experiments, in which was studied only the appearance of the virus disease in different potato varieties (Table 7), the potato plants were planted at distances of 0.30 x 0.65 metres. Experiments with Harbinger variety For the first field experiments carried out in 1946, Tammisto Plant Breeding Station provided tubers of the Harbinger potato variety. At that time its tuber yield appeared to be relatively high. In the following year (1947) the productiveness of the variety Harbinger in comparison with that of the other potato varieties in- vestigated was somewhat lower. The first observation on the appearance of the vi- rus disease were made in 1948. The diseased potato plants then amounted to 53 % of the whole; in the following year (1949) the corresponding figure was 89 %. The plants vegetatively descending from potato plants which had shown them- selves to be healthy in the preceding summer were studied from the year 1952; the corresponding rates of the diseased plants from 1952 to 1957 were as follows: 66 %, 46 %, 65 %, 89 %, 94 %, and 100 %. New, healthy setting tubers of the variety Harbinger were obtained from Inari in 1956. Some of the plants descended from these tubers showed symptoms of the virus disease as early as in 1957. The proportions of diseased plants vegetatively descended from potato plants which had seemed to be healthy in the preceding summer were in 1958 and 1959 corre- spondingly 64 % and 100 %. In 1960, again, tubers of healthy Harbinger potato variety were obtained from Inari. None of the plants grown from these tubers showed symptoms of the virus disease in the summer of 1960. These facts show that the virus disease appeared increasingly in the subsequent vegetative progenies of the potato plants which seemed to be healthy. Moreover, the average tuber yields of the Harbinger potato plants without symptoms were from year to year still lower per plant, or in 1953 1380 g., in 1954 1280 g., in 1955 820 g., and 1956 720 g. The corresponding yields of the variety Harbinger, the set- ting tubers of which were obtained from Inari in 1956, were in 1957 1 100 g., and in 1958 680 g. Further, in many cases, the symptoms of the virus disease appeared in the progenies of the seemingly healthy plants after their sprouting, and soon enough to convince one that the infection must already have taken place in the preceding summer (Table 1). Consequently, some of the healthy looking plants had also been in- fected by the virus. In 1954 and 1960, the plants were infected with potato late blight very early, and consequently in most cases the primary symptoms of the virus disease were perhaps not observed. On the other hand, the virus infection may often take place so late in the autumn that the visible symptoms do not become apparent before the lifting of the yield. In the summer of 1959, the temperature was higher and the precipitation lower than normal. There was practically no late blight to observe. On the contrary, large numbers of aphids appeared on the potato plants. The primary symptoms of the virus disease manifested themselves in the variety Harbinger from 24th to 27th 91 Table I. Dates of the appearance of virus disease in Harbinger potato plants descended from plants in which no symptoms had been observed in the preceding summer. Year Date of Date of Date of The disease became setting sprouting lifting visible 1953 27/5 12-19/6 12/9 22/6-21/7 1954 28/5 10-19/6 8/9 26/6- 3/8 1955 4/6 24/6- 1/7 24/9 27/6- 3/7 1956 2/6 15/6- 3/7 4/9 25/6-25/71 ) 1957 24/5 11-24/6 11-12/9 24/6-19/8 1958 5/6 18-28/6 11/9 28/6- 2/7 1959 15/5 1- 8/6 17/9 Ö/7-27/72 ) ') One potato plant showed virus symptoms on 27th July, the others at the turn of June and July. 2 ) One potato plant showed virus symptoms on 6th July, one on 16 th July, the others (18 plants) on 24th to 27 th July. July with unusual severity; the uppermost leaves of the plants died and turned brown as if damaged by frost (Fig. 2). Despite this, the amount of the tuber yield of these plants was relatively high (Table 4). Moreover, in other cases also the effect of the primary virus infection on the tuber yield was not very injurious (Table 2). On the contrary, the tuber yields of the vegetative progenies of the virus-infec- Fig. 2. In 1959, the primary symptoms of the virus disease in the potato variety Harbinger occurred with exceptional severity. 92 ted potato plants appeared to be low (Tables 3 to 4). Subsequently, the degenera- tion did not progress from one vegetative generation of the diseased plants to the next. Table 2. The effect of the date of appearance of the virus disease on the tuber yield of Harbinger potato in 1957 (the slight type of the virus disease). The disease No. of plants Tuber yield per became visible plant (g) Before 7th July 10 227 After 7th July 13 494 Healthy plants 2 1098 The symptoms of the virus disease varied in the differentpotato plants. Each of the types of symptom manifested itselfas unvarying from one vegetative generation of the potato to the next. Part of the vegetative progenies of one and the same healthy potato plant were affected by one, and part by another type of the virus disease. The severe type of the disease caused death of the lowermost leaves of the haulms, and green leaves were left only at the tops of the shoots (Fig. 3); the leaflets were wrinkled, and the whole of the plant withered early. The slight type of the disease also caused wrinkled leaflets, but the lowermost leaves of the plant did not die (Fig. 4). There wr as a distinct difference between the effect of these types of the disease on the amount of the tuber yield (Tables 3 and 4) as well as on that Fig, 3. Secondary symptoms cf the severe type of the virus disease in the variety Harbinger. 93 of the top yield (Table 5) of the potato. Moreover, there were intermediate forms of these two extreme types of the disease to be observed. In field experiments car- ried out in 1957 the average tuber yields per plant of the variety Harbinger affected by the different types of the virus disease were as follows; the slight type 281 g. (77 plants), the intermediate types 169 g. (32 plants), and the severe type 73 g. (37 plants). The disease had appeared in 1956 or earlier in the vegetative parents of all these plants. In the years 1957 to 1960, the rate of the tuber yield of the slightly diseased plants related to that of those with no symptoms averaged 27 % (Table 3); that of the severely diseased plants was about 5 % (Table 4). The effect of the inter- Table 3. The effect of the slight type of the virus disease on the tuber yield of the Harbinger potato variety. (In 1959 and 1960 no new plants showed any symptoms of this type of virus disease). Results Results Results Results The in 1957 in 1958 in 1959 in 1960 became No Yield/plant Nq Yield/plant Nfj Yield/plant Nq Yield/plant visible of No. g. fo No. g. of No. g. of No. g. (year) plants of plants of plants of plants of stud- tub- stud- tub- stud- tub- stud- tub- led ers ied ers ied ers ied ers 1953 24 10 379 25 6 240 10 6 391 15 9 447 1954 22 8 274 18 6 218 8 4 205 15 7 266 1955 11 9 255 24 5 202 10 5 310 15 8 312 1956 20 6 184 10 5 215 10 5 350 15 8 286 1957 23 13 377 17 5 163 10 4 194 15 4 129 1958 16 6 171 5 3 140 15 7 169 Without symptoms 2 30 1098 12 16 521 - 1 ) -») - 1 ) 19 20 1623 J) All the plants were virus diseased. Fig. 4. Secondary symptoms of the slight type of virus disease in the variety Harbinger 94 Table 4. The effect of the severe type of the virus disease on the tuber yield of the Harbinger potato variety. (In 1960 no new plants showed any symptoms of this virus disease). Results Results Results Results The in 1957 in 1958 in 1959 in 1960 became No ' Yield'plant No. Yield/plant No. Yield/plant No. Yield/plant visible of No.of g. of No.of g. of No.of g. of No.of g (year) plants tub- plants tub- plants tub- plants tub- stud- ers stud- ers stud- ers stud- ers ied ied ied ied 1953 10 4 117 10 3 64 6 2 130 14 6 147 1954 4 3 85 9 3 29 10 3 26 15 3 52 1955 14 3 58 II 2 18 5 2 34 11 3 26 1956 9 2 43 23 3 30 10 1 13 12 2 12 1957 I 9 263 10 3 24 8 2 19 14 2 8 1958 17 4 37 10 3 23 12 1 4 1959 15 27 838 15 0 33 Without symptoms 2 30 1098 12 16 521 —») -') —') 19 20 1623 ’) All the plants were virus diseased. mediate forms of the virus disease on the tuber yield of the potato is not referred to in the tables attached. Further, the two extreme types of the virus disease did not appear to be quite uniform. For example, the tuber yields of the plants vege- tatively descended from the Harbinger potato plants, which were in 1953 noted as being affected by the severe type of the virus disease, continued relatively high (Table 4). Correspondingly, the top yield of these plants appeared to be higher than that of the others (Table 5), even if the dying of their lowermost leaves was also apparent. On the other hand, the vegetative progenies of the plants which had been infected in 1956 to 1958 were very small-sized and their tuber yields very low (Table 4). The slight type of the virus disease seemed to be more uniform (Table 3). Table 5. The effect of the virus disease on the top yield of the Harbinger potato variety in 1956. The disease Top yield on 3rd Sept. per plant viable SUght type Severe type of virus disease of virus disease(year) 1953 36 ± 2 .1 20 ± 2.4 1954 38 ± 54 19 ± 3.5 1955 56 ± 43 15 ± 4.0 1956 58 ± 4.6 14 ± 4.0 Without symptoms 1956 • 155') 1551 ) *) Only 2 plants 95 According to serological investigations carried out in 1957 (cf. 6), virus S was present in most of the Harbinger potato plants studied. Virus S was present in plants with the severe types of symptom as well as in those with slighter symptoms, However, the sap of some of the diseased plants did not react positively with the antiserum against potato virus S, and, on the other hand, the virus also appeared to be present in 16 seemingly healthy plants descended from the tubers obtained from Inari in 1956. Consequently, virus S was hardly the cause ofthe virus disease studied. According to the findings of corresponding investigations, potato virus X was present in none of the 14 seemingly healthy, nor in the 52 diseased Harbinger potato plants investigated. By contrast, an antiserum against potato virus Y caused agglu- tination in the sap of most of the Harbinger potato plants. As in many cases the normal serum used also reacted positively with the sap of these plants, the result cannot be considered conclusive, however. Nevertheless, the secondary symptoms of the severe type of the disease were typical of the potato rugose caused by potato Table 6. The effect of the virus disease on the tuber yield of the variety Aquila. Results Results Results Hi,- in 1958 in 1959 in 1960 Yield/plant Yield/plant Yield/plant visible No.of No. of g. No.of No.of g. No.of No.of g. (year) plants tubers plants tubers plants tubers studied studied studied I9M 14 1 18 14 2 24 14 3 25 1957 5 11 431 20 5 122 15 4 44 1958 2 19 863 -') - l ) -') ->) -') -') 1959 17 25 2412 15 7 136 1960 19 3 79 Without symptoms 18 17 1192 2 28 2186 1 22 2622 ') No new plants diseased virus Y. The plants remained small, and their haulms were limp. The leaves became wrinkled, their structure was fragile, and at the beginning they were mottled in colour. There were light-brown-coloured, necrotic spots on the leaflets, and the leaves died, starting from the base of the haulms, until living leaves were left only at the tops of the shoots (Fig. 3). On the under side of the leaflets, the necrotic streaks which are typical of the potato rugose in many potato varieties during the primary phase of the infection, did not, however, occur in the variety Harbinger. Instead, there were to be observed on the leaflets shapeless, initially yellow, and later brown-coloured spots. For the slight and the severe types of the disease, the primary symptoms were almost alike. Instead, the secondary symptoms of the for- mer type of the disease occurred to a distinctly slighter extent, and the lowest leaves 96 of the shoots did not die. Neither of these two extreme types of the disease, nor any of the intermediate types changed in a single potato plant or its vegetative progeny into any another type of the disease. Almost all the vegetative progenies of the infected potato plants showed symp- toms of the virus disease. From the tubers of only one plant did both diseased and healthy potato plants arise. Experiments with A q nil a variety Healthy and virus-diseased plants both grew from the tubers of only one Aquila potato plant. In this plant, the primary symptoms did not appear until the 11th September (in 1957). In all other cases studied, each of the vegetative progenies of the virus-infected plants was diseased. Also in the variety Aquila, the symptoms of the virus disease did not in some instances become evident before the summer following the infection. For example, Table 7. Occurrence of virus disease in varieties Harbinger and Aquila in a field experiment, in which virus-infected Harbinger-potatoes were set between the experimental plots. Variety No. of diseased plants In litöH In 1959 In 1960 (20 plants) (20 plants) (30 plants) Harbinger 0 11 30 Aquila 0 1 4 in 1960 the symptoms of the virus disease appeared in the plants very soon after their sprouting (Table 8). Variety Aquila proved to be extremely resistant to potato blight. Consequently, this disease did not disturb the observation of the primary symptoms of virus disease in Aquila potato plants. When the primary symptoms did not appear before late in the autumn, the effect of the virus disease on the amount of the tuber yield of the potato plants was exceedingly minute (Table 9). On the other hand, the secondary phase of the virus-disease caused severe degeneration of Table 8. Dates of appearance of the symptoms of virus disease in the Aquila-potato plants descended from plants in which no symptoms had been observed in the preceding summer. Year Date of Date of Date of The disease setting sprouting lifting became visible 1957 24/5 12-25/6 12/9 9/8-11/9 1958 5/6 18-28/6 12/9 2/9- 5/9 1959 15/5 2- 5/6 19/9 31/7- 4/9 1960 30/5 13-30/6 15/9 30/6-14/7 97 Table 9. The effect of the date of appearance of the virus disease on the amount of tuber yield of Aquila- potato. Year The disease became visible Before 7th July After 7th July Healthy plants No.of Tubers/plant No.of Tubers/plant No.of Tubers/plant plants g. plants g. plants g studied studied studied 1957 14 1382 20 1864 Hl.-.s 2 863 18 1192 1959 17 2412 2 2186 1960 6 6 13 115 1 2622 the plants. The rate of the tuber yield of the virus-diseased plants in comparison with that of the healthy ones appeared to average only 6 %. In the variety Aquila, only the severe type of the disease was observed. It seems, however, that also this potato variety was affected by virus infections of varying severity in different years (Table 6). According to the results of a special field experiment (Table 7), virus infec- tions occurred much more frequently in Harbinger than in the Aquila potato variety. Serological investigations showed that potato virus X was not present in the diseased Aquila potato plants. Virus S was found in only some of the plants. An agglutination test with antiserum against virus Y gave a positive result in the sap of the majority of the plants, but the normal serum used also caused the same reaction. However, dark brown, necrotic streaks occurring on the under side of the leaflets, characteristic of the potato rugose caused by potato virus Y, were also the primary symptoms of the virus disease appearing in the variety Aquila. The secondary symptoms were almost the same as those characteristic of the severe type of the disease occurring in the variety Harbinger. Generally, the variety Aquila was infected only when growing in the immediate vicinity of virus-diseased Harbinger potato plants. Experiments with King George V variety In the potato variety King George V, the virus disease manifested itself in a way similar to its occurrence in the variety Aquila. The tuber yield of the diseased plants appeared to be very low (Table 10). Discussion The variety Aquila did not become virus-infected as frequently as the variety Harbinger (Table 7). The variety Harbinger has generally appeared to be particu- larly susceptible to the virus disease (2, 3, and 4). However, when the plants were virus-infected, the severity of the disease showedalmost exact correspondence in the three potato varieties studied (Tables 4,6, and 10). 98 The rate of the tuber yield of the diseased Aquila plants, in comparison with that of the healthy ones, averaged 6 % (Table 6). The corresponding figure for Har- binger was 5 % (Table 4). The productivity of the diseased plants of the variety King George V changed to a corresponding level (Table 10). In the experiments carried out by Brummer (2,3) with the variety King George V, the corresponding figure was nearly the same, or 9 %, but in experiments with the variety Harbinger Table 10. The effect of the virus disease on the tuber yield of the variety King George V.l ) Results Results The disease in 1958 in 1959 . ~, „ , Yield/plant ~ , Yield/plantvisible No.of JL No.of i£ (year) plants No.of g. plants No.of g. studied tubers studied tubers 1956 4 2 18 4 1 11 1957 9 5 48 9 3 17 1958 4 4 31 7 14 1959 8 17 2005 Without symptoms 1 15 787 - 2 ) - 2) - 2 ) ') The tuber yield in 1960 of the vegetative progenies of plants (13) which had been infected in 1956 was 22 g (3 tubers) per plant. 2 ) No healthy plants. it was noticeably higher, or 32 %. In our investigations, apart from observation of the severe type of the disease (Table 4), attention was directedto a slight form (Table 3), and to intermediate ones. Their nature was characteri ed by the tuber yields (Tables 3 and 4), and the top yields (Table 5), as well as by the character of the secondary symptoms (Figs. 3 and 4). It is known that in some potato varieties a simultaneous infection by viruses Y and X causes symptoms which resemble those characteristic of the slight type of the virus disease occurring in the potato variety Harbinger (cf. 5). In the case exam- ined in this paper, however, a simultaneous infection was hardly possible, because the different types of the disease, without exception, retained their special features from one vegetative generation of the potato to the next. According to the results of the serological investigations, virus X was not present in the potato va- riety Harbinger; the varieties King George V and Aquila also were not infected by potato virus X. Further, in some cases, tubers of one and the same Harbinger potato plant developed plants of which some were infected by the slight type and some by the severe type of the virus disease. Consequently, somatic mutations (cf. 6) can hardly have been the reason for the appearance of the different types of the disease. Thus the fact that none of the different types of the virus disease observed in the variety Harbinger changed to any other type of virus disease in the following vegeta- tive generations of the potato, may indicate that different viruses occasioned the 99 disease, and each virus type caused premunity, which prevented a new infection of the plant, i.e., the different types of symptom occurring in the variety Harbinger were probably caused by dif- ferent races of the same virus species. In the potato varieties Aquila and King George V, only the severe type of the disease was observed. Moreover, in these potato varieties the primary symptoms (leaflets a little wrinkled, and small dark brown necrotic streaks on the underside of the leaflet) appeared to be clearly different from those displayed in the variety Harbinger, in which uniform areas of the leaflets turned brown. However, it is known (cf. 5), that one and the same virus species causes different kinds of symp- toms in different potato varieties. Futher to this, in all these potato varieties the secondary symptoms of the severe type were almost identical. Again, the potato varieties King George V and Aquila became virus-infected only after cultivation in the immediate vicinity of the virus-diseased Harbinger potato plants. Consequently, it is presumed that the virus diseases which appeared in all the three potato varieties were caused by one and the same virus species. Antiserum against potato virus Y gave a positive reaction. It is true that this result cannot be considered conclusive, as the normal serum used also reacted posi- tively with the sap of the plants. On the base of the symptoms, the virus disease concerned seems to be the potato rugose, caused by potato virus Y [Solanum virus 2 (Orton) Smith]. It is known (cf. 8) that many races which cause different kinds of symptom in one and the same potato variety belong to this virus species. Virus S was present in many plants of the potato varieties studied. However, no correlation was observed between the appearance of this virus species and the symptoms occurring in the potato plants. The effect of the potato virus S on the potato plant is also generally very slight, or the infection could be of a quite latent nature (1,7). Conclusions The virus disease occurring in the potato varieties Harbinger, Aquila, and King George V was probably the potato rugose caused by potato virus Y ( Solanum virus 2). In the variety Harbinger, the degree of strength of the virus disease probably varied as a result of the appearance of different races of potato virus Y. The type of the virus disease did not change from one vegetative generation of the potato to another. In the potato varieties Aquila and King George V, only the severe type of the disease was observed. The severe type of the virus disease reduced the tuber yield of all the potato varieties investigated to a level of 5 to 6 %, and the slight type occurring in the va- riety Harbinger to an average of 27 % of the normal. The virus infection appeared more frequently in Harbinger than in the variety Aquila. 100 In the summer, when the infection of the potato plant took place, the virus disease reduced its productivity only relatively little. In the following vegetative generation of the diseased potato plants, the degree of their degeneration conclu- sively displayed itself. Following this, the wakening of the virus diseased plants did not progress further from one vegetative generation to the next. REFERENCES (1) Aura, Klaus 1957. Suomessa viljellyn perunan virustaudeista (On potato virus diseases in Finland) Maatal.tiet. aikak. 29: 103—110. (2) Brummer, Veikko 1946. Tutkimuksia tärkeimmistä Tammistossa esiintyneistä perunavirooseista. Hankkijan siemenjulk. 1946: 176 185. (3) —»— 1949. Vesijärven jaTammiston aikaisen suhtautumisesta perunavirooseihin (On suscepti- bility to the virus diseases of Harbinger and Tammisto Early potatoes). Maatal. tiet. aikak. 21; 17 28. (4) Jamalainen, E. A, 1946, The significance of potato virus diseases in Finland. Ibid. 18: 134 146. (5) Klinkowski, Maximilian 1958. Pflanzliche Virologie 11. Berlin. (6) Pohjakallio, Onni & Karhuvaara, Laura 1960. Resistance to virus diseases of soine Fl-clones descended from the species hybridization Solanum demissum x S. tuberosum. Maatal. tiet. aikak. 32: 73 80. (7) Ronde Kristensen, H. 1956. Kartoffel Virus S. Ugeskr. for lantm. 101: 323 326 (8) Smith, Kenneth 1957. A Textbook of Plant Virus Diseases. Boston. SELOSTUS: VIIRUVIROOSIN VAIKUTUKSESTA PERUNAN SADON MÄÄRÄÄN Onni Pohjakallio, Laura Karhuvaara ja Simo Antila Yliopiston kasvipatologian laitos, Helsinki Helsingin yliopiston Viikin koetilalla suoritetuissa kokeissa esiintyi Vesijärvi-, Aquila- jaKuningas Yrjö V-perunoissa runsaasti virustautia, joka todennäköisesti oli viiruviroosia. Vesijärvi-perunassa tau- din ankaruus suuresti vaihteli. Vaihtelu nähtävästi johtui viiruviroosin aiheuttajan (perunan Y-virus 1, Solanum virus 2) erilaisten patogeenisten rotujen esiintymisestä. Taudin ankaruustyyppi ei sairaan kas- vin kasvullisesta sukupolvesta toiseen kertaakaan muuttunut. Aquila- samoin kuin Kuningas Yrjö V- perunassa esiintyi vain taudin ankaraa tyyppiä; se heikensi tutkittujen perunalajikkeiden satoisuuden 5 6 prosenttiin normaalisesta. Vesijärvi-perunassa esiintyi myös virustaudin lievää muotoa, joka ai- heutti satoisuuden alenemisen keskimäärin n. 27 prosenttiin terveen perunan satoisuudesta. Virustauti- tartunnan sai Vesijärvi-peruna paljon herkemmin kuin Aquila. Perunan satoisuuden heikentyminen oli saastumiskesänä vain osittaista, mutta sairaan kasvin jo ensimmäisissä kasvullisissa jälkeläiskasveissa se ilmeni lopullisena. Seuraavissakasvullisissa sukupolvissa ei tauti enää aiheuttanut perunan lisäänty- vää surkastumista.