The severe strain of potato spindle tuber viroid (s‐PSTV) as well as chrysanthemum stunt (CSV) and cucumber pale fruit (CPFV) viroids were found to be transmitted through seed and pollen of the tomato cvs. Rutgers and Najwcześniejszy. Plants pollinated with a pollen infected with any of these three viroids became systematically infected. Plant, fruit and seed symptoms of viroid infection were noted on sap‐ and pollen‐inoculated plants and the yield of these plants was reduced. Tomato cv. Rutgers plants grown from infected seeds were symptomless although all three viroids were detected in these plants by bioassay and by electrophoresis on 5% polyacrylamide gel. When DNA complementary to s‐PSTV RNA was used for a direct viroid detection in seed samples by spot hybridization technique it hybridized not only with s‐PSTV RNA but also with CSV RNA as well as with CPFV RNA.

Isolation of RNA from plants rich in secondary metabolites using commercial kits often results in contaminated preparations which are not suitable for downstream applications. Although many specific protocols appropriate for plants with a high content of phenolics, anthocyanins and polysaccharides have been developed, these are often expensive, time consuming and not applicable to different types of tissues. This study presents a simple and efficient modification of RNA extraction from different types of tissues using two commercial reagent kits. By simple improvement, we routinely obtained high-quality RNA of the following plants: the blackcurrant bush, black chokeberry bush, pear tree, apricot tree, apple tree, hardy kiwi, tangerine tree, highbush blueberry and cranberry plant.

Viroid-free potato and chrysanthemum plants were obtained from meristem-tips cut from potato spindle tuber viroid-infected potato plants and from chrysanthemum plants infected with chrysanthemum stunt, chrysanthemum chlorotic mottle or cucumber pale fruit viroids after 6 months therapy in a growth chamber at 5 °C and 16 hours daily light of 5.000 lx intensity. Chrysanthemum plants survived quite well the conditions of therapy while potato plants grown from stem cuttings survived these conditions much worse and potato plants grown from tubers did not survive these conditions. PSTV-free plants were obtained from meristem-tips cut from sprouts grown from potato tubers infected with severe (s-PSTV) or mild (m-PSTV) strains of potato spindle tuber viroid after 6 months therapy at 6-7 °C in the dark. The tubers survived these conditions quite well.The 3 months therapy period was found too short for any plant material. The efficiency of 6 months therapy in viroid elimination varied for different viroids and different plant material from 18.5 to 80.0 %.

Prune dwarf virus (PDV) isolates have been investigated for genetic diversity. Full-length nucleotide and amino acid sequences of viral coat protein from 23 isolates collected from different stone fruit trees (sour and sweet cherry trees, wild cherry tree, plum tree, almond tree, peach tree) and different countries (Poland, Italy, Germany, USA, Israel) were analysed and compared to 57 others available in GenBank. Comparison of all sequenced virus isolates revealed diversity of 86-100 % at nucleotide level and 79-100 % at amino acid level. The ratio of non-synonymous to synonymous polymorphic sites indicated that purifying selection dominated in case of PDV. However, six codons showed to be under strong positive selection, including the codon located inside the structure involved in RNAbinding activity.

Garlic plants can be infected by different viruses including eight which belong to the genus Allexivirus, family Alphaflexiviridae. The aim of the research conducted was to detect and identify the allexiviruses GarV-A,

The host‐ranges and the reactions of particular plant hosts to inoculation with severe (s‐PSTV) and mild (m‐PSTV) strains of potato spindle tuber viroid, as well as with chrysanthemum stunt viroid (CSV) and cucumber pale fruit viroid (CPFV) were quite similar. Some minor differences did not exceed the limits of differences noted for the strains of the same plant viroid. Two‐directional crossprotection was noted for each viroid pair when s‐PSTV, m‐PSTV, CSV and CPFV were tested on chrysanthemum cv., ‘Bonnie Jean’ plants. Finally, the relative mobility of RNAs of s‐PSTV, m‐PSTV, CSV and CPFV on 5% polyacrylamide gel was identical, no matter what extraction method from plant material was used. We postulate that these four plant viroids may be regardedas the strains of the same plant viroid “species”. On the other hand, chrysanthemum chlorotic mottle viroid (ChCMV) appeared to be a quite different plant pathogen. This viroid infected and caused symptoms only in chrysanthemum plants, and was able to infect and induce symptoms on plants which had already been infected with any other viroid studied, and it did not protect chrysanthemum cv. ‘Bonnie Jean’ plants against any of the other viroids. We were not able to locate a ChCMV‐RNA band on polyacrylamide gel.

Blueberry scorch virus (BlScV) is a member of the genus Carlavirus and one of the most widespread pathogens of highbush blueberry (Vaccinium corymbosum L.). The virus was first reported in the United States and has been reported in several countries in Europe, including Italy, Germany, the Netherlands, and Poland. Symptoms of scorch disease in highbush blueberry include necrosis of flower blossoms and leaves, shoot blight, and chlorosis. Sometimes BlScV infection is symptomless or limited to single blossoms and shoots, but all highbush blueberry cultivars are susceptible to virus infection. Cranberry (V. macrocarpon L.) and wild black huckleberry (V. membranaceum L.) are known as natural and symptomless hosts of BlScV (1). In June 2012, during the research concerning the occurrence of BlScV in plants outside Vaccinium sp., 15 leaf samples from five elderberry bushes (Sambucus nigra L., family Adoxaceae) were randomly collected from the Lodzkie region in Central Poland and three were positive in double antibody sandwich (DAS)-ELISA using specific antiserum (Agdia Inc., Elkhart, IN). To confirm the presence of the virus, total nucleic acid was extracted from ELISA-positive elderberry samples according to established protocol (T. Malinowski. Proc. 4th Int. EFPP Symposium, 445, 1996) and used in one step reverse transcription PCR. Primers were developed against the published NJ-2, BC-1, and BC-2 sequences of BlScV (GenBank Accession Nos. NC_003499, AY941198, and AY941199, respectively). The forward primer, RDP_1 (5′-ATGGCACTCACATACAGAAGTCC-3′), and the reverse primer, RDP_2 (5′-TGCCTCTTCAATGCACGATGTTC-3′), were used to amplify a 420-bp fragment of the RNA-dependent RNA polymerase gene of the virus. Amplicons of expected size were obtained from three DAS-ELISA-positive samples, while no products were observed for the negative control (DAS-ELISA-negative elderberry tissues). Sequence of one selected PCR product revealed 100, 88, and 87% nucleotide sequence identity and 100, 96, and 96% amino acid sequence identity with BC-2, NJ-2, and BC-1, respectively. BlScV-infected elderberry bushes were asymptomatic. As BlScV is transmitted by aphids in a non-persistent manner, infected elderberry bushes near highbush blueberry plantings may play an important role in virus spread. The potential for BlScV infection of plants outside family Ericaceae should be investigated. To the best of our knowledge, this is the first report of BlScV infecting elderberry. Reference: (1) R. R. Martin et al. Viruses 4:2831, 2012.

Prunus necrotic ringspot virus (PNRSV) is a rose and stone fruit tree pathogen. Three different PNRSV isolates, originating from three rose cultivars were studied. These PNRSV isolates were characterized using molecular techniques. Nearly the complete nucleotide sequence (1,630 nucleotides) of RNA3 of the isolate PNRSV-R1 has been determined (GenBank Acc. No. DQ003584). The sequence of the MP gene of the PNRSV-R1 isolate was determined, the first such results for a rose-derived PNRSV isolate. The reaction of PNRSV infection on test plants was also investigated. Cucumis sativus cv. Wisconsin, Cucurbita maxima cv. Buttercup and Cucurbita pepo cv. Melonowa _ Zółta appeared to be the most useful test plants for the differentiation of isolate-specific pathogenicity.