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POTENTIAL OF RIBAVIRIN FOR TREE FRUIT VIRUS INHIBITION
In order to evaluate the potential inhibitory effect of the compound upon tree fruit viruses, we sprayed groups of four Chenopodium quinoa indicator plants with three concentrations of ribavirin and subsequently inoculated the leaves with eight tree fruit and grape viruses (American rasp leaf; apple chlorotic leaf spot; apple stem grooving; cherry leaf roll – golden elderberry strain; grape fanleaf; prune dwarf; necrotic ringspot – cherry isolate and rugose mosaic; an unidentified cherry isolate), and one PVY-virus (guar latent). Potato plants systemically infected with the spindle tuber viroid were treated similarly.
Lesion numbers, virus concentration, systemic movement, interval between compound application and symptom appearance as well as results of backchecks were identical in treated and untreated plants, except in the case of apple chlorotic leaf spot virus (CLSV).
Under early spring greenhouse conditions (approx. 4000 lux) foliar application of 500 ppm ribavirin with 0.02% surfactant to C. quinoa plants completely prevented CLSV multiplication and lesion formation.
A similar effect was obtained with applications of 2000 ppm under growthroom (approx. 8000 lux) and late spring greenhouse (approx. 15000 lux) conditions.
In a separate experiment, 1-year-old CLSV infected apple trees were sprayed at weekly intervals during the growth period with 500 ppm ribavirin.
Indexing of the apple shoots to C. quinoa during the following spring showed that no virus was detectable in the shoots formed during the previous year, while all untreated controls contained the virus.
When shoots from similarly CLSV-infected apple trees were exposed to 20, 40, and 80 ppm ribavirin in meristem culture media (approx. 4000 lux), no virus was detectable in any of the cultures after two growth periods of 4 weeks each.
All meristem cultures growing on normal medium retained the virus.
Some phytotoxicity was apparent in the 80 ppm cultures.
The results show that CLSV multiplication and systemic movement can be prevented by foliar sprays or meristem culture treatment with ribavirin at sub-phytotoxic levels.
This opens the possibility of substituting rivabirin treatment for heat treatment when trees are infected with CLSV only.
In such cases, ribavirin treatment is a