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.
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 %.
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.
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