| Apple -- Latent Virus Diseases |
| Cause: Three viruses generally considered as "latent" in apple are Apple stem grooving virus (ASGV), Apple stem pitting virus (ASPV) and Apple chlorotic leafspot virus (ACLV) all of which are not too important in commercial apple production. ASGV causes Apple Decline on Virginia crabapple, ASPV causes Apply Spy 227 epinasty and Spy decline while ACLV causes Apple chlorotic leafspot on many crabapple cultivars (also called Apple top-working disease in Japan). The three viruses do not cause symptoms on most commercial cultivars. However, specific strains of one of these agents may be associated with diseases such as apple green crinkle disease and apple dead spur. |
| Symptoms:
Rootstocks of M. sylvestris 'Virginia Crab' respond to Apple stem grooving virus by developing a brown necrotic line at the graft union where complete breakage often occurs. Apple stem pitting virus also causes significant pitting and weakening of 'Virginia Crab' rootstocks.
Apple top-working disease in Japan was the result of a hypersensitive reaction of rootstocks (M. prunifolia var. Ringo) to Apple chlorotic leafspot virus in apple scions. The hypersensitive reaction at the graft union resulted in weakened trees with reduced production, and the weak graft unions were very susceptible to wind damage. Some of the new cold-tolerant and fireblight-resistant rootsotcks are hypersensitive to one or more of the latent viruses. |
| Cultural control: Use only virus-certified propagation material and rootstocks. |
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References: Mink, G. I. In: Virus and Viruslike Diseases of Pome Fruits and Simulating Noninfectious Disorders. P. R. Fridlund, ed. Washington State Cooperative Extension, Pullman, WA. Publication SP0003. |
| Content edited by: Ken Eastwell on January 1, 2009 |
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