Analysis of the immunoreactivity of several polyclonal antisera to potato virus X (PVX) with short synthetic peptides covering the entire amino acid sequence of PVX coat protein revealed immunodominant regions at the N- and C-terminal ends of the coat protein. In addition antigenic epitopes were also found in the central part of the coat protein. The immunoreactivity to the synthetic peptides was found to correlate with surface characteristics, i.e., hydrophilicity, calculated polypeptide chain flexibility and with the vicinity of potential beta turns. Characterization of the antigenic properties of PVX will facilitate the development of detection methods for potexviruses.

A simple kit for rapid detection of potato virus Y by latex serological test was developed. The test is carried out on a white cardboard sheet and the results can be read by naked eye in two minutes. A test card of 10 x 6 cm holds latex sensitized antibodies, buffers and other necessary ingredients as dry blue colored formulate on the ringed areas of the card. A test card includes space for six tests and positive and negative controls. The kit also includes disposable plastic sticks for mixing the samples with test reagents and a hand press with disposable plastic tips. For testing, dried reagents are dissolved in drops of sample and mixed. After gentle rotation, samples containing virus appear clearly granulated while samples from healthy plants remain unagglutinated. The testing of undiluted extracts of evenly developed tuber sprouts resulted in over 91 % identity with the results obtained with ELISA that was used as a control method. Testing of diluted leaf extracts reached the same reliability but undiluted leaf extracts from glasshouse grown potatoes were not well suitable as test samples because of their dark green color. No such problems occurred with field grown material and a complete identity with the ELISA readings was true when the samples included secondarily infected potato plants. No reaction to other potato viruses than PVY was obtained by the test kit.

Air-borne secondary inoculum of Bipolaris sorokiniana caused severe foliar diseases and yield losses in all 12 spring 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. Infection incidence as well as fungal invasion of the internal cell leyers of the grains varied significantly among barley cultivars. The most susceptible of those tested were cvs. Teemu, Paavo and Pomo, while the most resistant were Ingrid, Otra and Pirkka.

Soil-borne infection of Bipolaris sorokiniana caused foot and root rot in all spring barley cultivars studied. Significant differences in susceptibility of the cultivars and pathogenicity of the fungus isolates were found. Primary symptoms caused by the fungus were seedling blight, later foot and root rot. Yield losses caused by the fungus varied from 3 % to 33 % the mean being c. 15 %. Yield losses could occur without severe disease symptoms. Toxic metabolites produced by the fungus induced visible foot and root symptoms in all cultivars tested and caused lesions in the leaves of some cultivars. Variability in toxin production of fungus isolates as well as the reaction of a cultivar to toxins was demonstrated. The cultivars most susceptible to soil-borne infection by the fungus also showed the most severe symptoms when exposed to toxic metabolites of the fungus.

Seed-borne infection by Bipolaris sorokiniana decreased the percentage germination of barley seeds and the emergence of seedlings. Infection levels were higher in non-germinated than in germinated seeds. Seed treatment with organomercurial fungicide or imazalil improved the percentage emergence but a low number of diseased seedlings still remained in the crops. The fungus caused a reduction in grain yields in most experiments and also decreased their value as sowing seed, if the weather conditions were favourable for compute disease expression. Yield losses in greenhouse experiments varied from 7.2 to 38.5 % and in the field from 5 to 11 %, and showed a strong correlation with the infection levels in the seed stocks. Higher losses were associated with the six-row cultivars. Organomercury seed treatment resulted in a slight but in significant increase in yields but it was able to prevent an occurrence of secondary infection in the crop resulting in a lower seed infection levels of the grain. In field experiments in Inari (69° N.L.) seed-borne inoculum could be demonstrated clearly to be the only source of a severe disease outbreak. The inoculum remaining in the soil was capable of initiating soil-borne infection of barley seedlings during the following two growing seasons.

High titered and highly virus-specific antisera to selected PVYo and PVYn antigens and their mixture were produced in rabbits. Immunoglobulins purified from the antisera with the protein A method and their enzyme conjugates had very strong virus-specific but no non-specific reactions in the ELISA test. Their homologous reactions to the antigens were stronger than heterologous but any PVY isolate could be identified in a potato leaf sample with the dilutions between 10-2 and 10-3 and in a sample from sprouted tubers with secondary infection diluted between 10-1 and 10-2.

Bipolaris sorokiniana is reported as a common fungus in commercially grown barley seed in Finland with possible economic importance. In 1974, when 200 samples of barley seed were surveyed the fungus was identified in 60 per cent of samples. The three following years the incidence was 19, 29 and 38 %. The mean per cent seeds infected was 3.8, 1.3, 1.2 and 1.9 respectively. The highest recorded individual % was 92. The most severely infected cultivar was Paavo each year. In most cases only the seed cover was invaded by the fungus but also infection in the embryo and the cell leyers surrounding it was observed. Such severely infected seeds did not germinate or the seedlings were readily infected after germination. B. sorokiniana was less frequent in the western parts of the country. Field experiments in 1972—1979 confirmed the same varietal susceptibility which was found by the survey of commercial samples of barley seed. High rainfall and relative humidity in July and August were the main factors associated with increased seed infection incidence.

Damping-off occurred in 90 % of the spring oilseed rape fields surveyed in 1981—1982. On the average, 10 % of the plants were infected with damping-off.6 % of the fields were severely infected (> 30 % of the plants affected) by damping-off and 38 % were uninfected or only slightly infected ( ≤ 5% of the plants affected). The incidence of damping-off was higher in those fields which had been under oilseed rape in earlier years. Ina crop rotation experiment, the amount of damping-off increased from 2 % to 20 %, and finally to 38 %, depending upon whether turnip rape had been grown on the same part of the field once, twice or three times. Crops other than Cruciferous ones were grown for 1 or 3 years between the turnip rape crops. Rhizoctonia solani Kühn was isolated from 76 % of the affected plants. The R. solani isolates produced severe damping-off on rape and turnip rape in pathogenicity tests. R. solani isolates from barley, potato and lettuce brought about only mild cases of damping-off, or else only a decrease in the growth of the plants. Fusarium avenaceum Sacc. was the only other isolated fungus which was pathogenic.

The occurrence of potato viruses in Finland and alternative methods for their identification are reported in this study. The following seven viruses were found to occur; potato viruses X, S, M, Y, A, potato leaf roll virus (PLRV) and tobacco rattle virus (TRV). The isolates of potato viruses X and Y included two clearly distinct strains. The other viruses had only minor variants. The most severe and important of the viruses was PVY, particularly its Y° strain. Other important viruses were PVM and PVA and potentially PLRV. PVY was found to be the most easily transmitted in the field. For serological identification of the viruses, indigenous antisera produced for selected isolates were mostly used. Significant serological variation was only found among the PVY isolates. The lowest concentration of PVX D-protein detected with the agar gel double diffusion test was 10 µg/ml and 1 µg/ml with the single diffusion test. With the ELISA test 0.1 ng of virus /ml could be detected. For PVX the lowest relative value detected in potato leaf sap was a dilution of between 10-6 and 10-7. The chloroplast agglutination test was too unreliable for detecting PVY in potato samples. Also the agar gel double diffusion test was found to be too insensitive for the identification of potato viruses but the single diffusion test could be used in certain cases. With the ELISA test potato viruses X, S, M and Y could be reliably detected in potato leaf sap and with almost the same accuracy in sap from sprouting tubers. The ELISA test was also found to give satisfactory results during routine testing for the identification of PVA and PLRV in potato leaves or non-dormant tubers.