Hop stunt viroid (HSV), cucumber pale fruit viroid (CPFV) and potato spindle tuber viroid (PSTV) were inoculated to 11 test plants in
Cucurbitaceae,
Solanaceae and
Compositae. Both HSV and CPFV developed symptoms on cucumber (
Cucumis sativus),
C. melo,
Benincasa hispida,
Lagenaria siceraria var.
clavata and
L. siceraria var.
microcarpa. Cucumber plants infected with HSV and CPFV showed stunting, vein clearing and leaf curling 14-17 days after inoculation. The other 4 plants in
Cucurbitaceae also showed stunting, leaf curling and top necrosis 16-22 days after inoculation, and severely infected plants semetimes died. It was found that tomato plants caused symptomless infection by HSV and CPFV. In tomato plants, concentration of HSV was lower than that in cucumber plants. No seed transmission was detected in HSV infected tomato. On the other hand, tomato plants infected with PSTV developed severe stunting and epinasty about 14 days after inoculation, but cucumber,
C. melo,
B. hispida,
L. siceraria var.
clavata,
L. siceraria var. microcarpa,
Citrullus vulgaris and
Cucurbita moschata in
Cucurbitaceae were not infected with PSTV. Similar scanning patterns of nucleic acid extracted from HSV and CPFV infected tomato (cv. Rutgers) were shown on 5% polyacrylamide gel electrophoresis, and infectivity assays from the gel fractions indicated that the migration rates of HSV and CPFV were almost identical. In this experiment, however, HSV and CPFV displayed identical migration rate with 7S RNA from healthy plant extracts, and thus no viroid-specific band was observed. Whereas, extractions from PSTV infected tomato displayed a typical specific band on 5% polyacrylamide gel electrophoresis, and PSTV activity was associated with this band. The results obtained indicated that pathogenic properties and molecular weight of HSV were very similar to those of CPFV. and different from those of PSTV.
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