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Symptoms may appear on leaves or fruits. They are particularly conspicuous on leaves in spring: chlorotic spots, bands or rings, vein clearing, or even leaf deformation in peaches. Some peach cultivars may also show flower breaking symptoms. Infected fruits show chlorotic spots or rings.
Diseased plums and apricots are deformed and show internal browning of the flesh; apricot stones show pale rings or spots (Dunez, 1987). Symptoms of sharka depend very much on the locality, the season, Prunus species and cultivar, and plant tissue (leaf or fruit) (Dosba et al., 1986; Kegler and Hartmann, 1998; Nemchinov et al., 1998a).There is no anti-virus treatment available to control sharka disease in orchards. However, there are considerable differences in susceptibility between the cultivars available for use in countries where infection is widespread (Hamdorf, 1986; Kegler et al., 1989; Mainou and Syrgianidis, 1992). Biological control by inoculation of trees with hypo-aggressive strains has not been as successful in the field as under controlled conditions (Kerlan et al., 1980).
Other effective control methods are to produce healthy plants for planting within a certification system, to control aphid vectors by regular treatment with aphicides, and to destroy diseased trees in orchards. Such methods are being used to contain PPV in several countries (for example, France and Italy) (Barba, 1998; Kegler and Hartmann, 1998).
EPPO recommends a certification scheme for fruit trees, which takes account of PPV (OEPP/EPPO, 1991/1992). Resistance to PPV has been reviewed by Dosba et al. (1994) and Kegler and Hartmann (1998) and this approach shows some promise, whether by traditional breeding or selection by transgenic methods (Câmara Machado et al., 1992b; Escalettes et al., 1994; Ravelonandro et al., 1998b; Scorza et al., 1998). New PPV-resistant plum, apricot, peach, and nectarine cultivars were bred or selected with different types or mechanisms of PPV-resistance (Hartmann, 1998; Kegler and Hartmann, 1998; Lahmatova et al., 1998; Paprtsein et al., 1998; Polák, 1998; Rankovi and Paunovi , 1989; Toma et al., 1998; Scorza et al., 2007). Studies of resistance to PPV in apricots showed that resistance appeared to be under simple genetic control involving one gene locus (Karayiannis, 2006).
EPPO recommends that all imported host material (except seeds) should come from a field subject to growing-season inspection. If the virus is present in the exporting country, this inspection should also concern the immediate vicinity of the field, and the material should derive from tested mother plants (OEPP/EPPO, 1990).
