Apple latent viruses
Apple chlorotic leaf spot virus (ACLSV)
Apple stem grooving virus (ASGV)
Apple stem pitting virus (ASPV)
Latent viruses are viruses that survive in their host without causing symptoms. These viruses are transmitted when a virus-infected scion is grafted onto a susceptible rootstock. There are number of latent viruses that affect apple, but these three are the most common. They may occur together, in pairs, or singly. Affected trees begin to show a general decline 1–2 years after grafting. Familiar symptoms associated with the specific viruses are: ACLSV, chlorotic leaf spots, leaf distortion, or leaf stunting (A); ASGV, chlorotic leaf spots, stem grooving and pitting, union necrosis, and swelling above the graft union (B); ASPV, pitting and grooving, epinasty and decline (C).
Common to all fruit-growing regions in eastern North America.
Depending upon the virus or virus combinations infecting the host, symptoms can be confused with apple union necrosis and decline (TmRSV), various nutritional deficiencies, and any disease or disorder that results in a general decline of the tree.
No natural vectors are known for any of the three viruses; infected trees can grow adjacent to healthy trees for years. These viruses are expressed only when an infected scion has been grafted onto a susceptible rootstock. The Geneva series rootstocks, in particular G.16, G.30 and G.65, are susceptible to one or more of the latent viruses, thus virus-free scions must be used with these rootstocks. Most other rootstocks, including the Malling (M) series and the Malling-Merton (MM) series of rootstocks, are tolerant to these viruses.
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