| Apple -- Scar Skin and Dapple Apple | |||
| Cause: These diseases are caused by Apple scar skin viroid. Many infected cultivars do not express symptoms of disease. It has become a problem when old orchards are top worked, and the new is susceptible to the viroid that had been symptomless in the original cultivar. Pear also appears to be a symptomless carrier of Apple scar skin viroid. The pathogen occasionally spreads slowly in the orchard, but the mechanism(s) is not known. | |||
| Symptoms: Affected fruit bears small circular spots near the calyx end of the fruit. As the fruit matures, the spots enlarge and the spots increasingly contrast with the darkening background color of the fruit. Larger spots may coalesce to form a broad band of dappling. In the case of the more severe scar skin, the circular patches become brown and necrotic, and fissures appear on the fruit. The affected fruit is smaller than fruit of non-affected trees. | |||
|
|||
| Cultural control: Control is achieved by the use of virus-tested (and found to be free of all known viruses) certified material. | |||
|
References: Hadidi, A. and Yang, X. 1990. Detection of pome fruit viroids by enzymatic cDNA amplification. Journal of Virological Methods 30:261-270. Hadidi, A., Hansen, A. J, Parish, C. L., and Yang, X. 1991. Scar skin and dapple apple viroids are seed-borne and persistent in infected apple trees. Research In Virology 142:289-296. |
|||
| Content edited by: Ken Eastwell on January 1, 2009 | |||
In print since 1954 and on the web since 1996. Questions or comments, please contact us.