|Riassunto in Inglese:|
Plum pox or sharka disease, caused by the Plum pox virus (PPV) was detected in the early 1900’s in Bulgaria and Macedonia and was first described by Atanasoff in 1932 (Kegler and Hartmann, 1998; Németh, 1986). The disease thereafter was observed on apricots in Bulgaria and on peaches in Hungary and Germany and it has progressively spread to fruit-producing areas of most European countries (Németh, 1986), then to the Mediterranean region (Roy and Smith, 1994). In the 1990’s the disease was observed on sour and sweet cherry trees in Moldova, Italy, Romania and Hungary (Nemchinov et al., 1998a). Plum pox disease has been recognized for years as the most important viral disorder of stone fruit trees in Europe and the Mediterranean region. The losses caused by PPV may be dramatic - in some cases they may reach 100% of fruit yields in susceptible cultivars (Kegler and Hartmann, 1998; Németh, 1986; Nemchinov et al., 1998a; Waterworth and Hadidi, 1998). European plums may show premature fruit drop, while Japanese plums and peaches show ring spotting on fruit, and apricots show serious fruit deformation. The disease impact is, however, modulated to a large extent by the variability in susceptibility/tolerance shown by individual cultivars of its Prunus host species.
In addition to apricot, plum, peach and cherry, several ornamental and wild Prunus species have been identified as natural and/or experimental hosts of PPV, although the significance of these species in the epidemiology of the diseases is largely unknown (James and Thompson, 2006; Damsteegt et al., 2007). PPV also infects some non-Prunus woody species and a number of herbaceous hosts (Németh, 1986; Virscek Marn et al., 2004; Llácer, 2006; Polak, 2006).
In 1994 the presence of PPV was verified in Chile and it is now considered widespread there (Herrera et al.,1998). PPV has also been detected in Argentina (Dal Zotto et al., 2006). In 1999 PPV was detected in Adams County, Pennsylvania, USA, and extreme quarantine measures to avoid its spread have been implemented by the U.S. Government (Dunkle, 1999) in the hope that this would contain the virus before it would have a chance to spread to other parts of the North American continent. However, PPV was detected in Ontario and Nova Scotia, Canada in 2000 (Thompson et al., 2001) and in July 2006, the virus was identified in two plum trees in Niagara County, New York, U.S.A. A month later, it was identified on peach trees, also from Niagara County, in a site in close proximity to a confirmed positive site in Ontario, Canada (Cornell University, 2008). Also in August 2006, in Michigan, U.S.A., a positive find of the virus was reported (Cornell University, 2008). Despite the additional sites found in New York and Michigan, as of 2009, no PPV had been detected in Pennsylvania or Michigan for three growing seasons after effective implementation of quarantine and eradication procedures. PPV was also reported infecting stone fruits in Asian countries such as China (Navrátil et al., 2005), India (Bhardwash et al., 1995), Pakistan (Kollerová et al., 2006) and Kazakhstan (Spiegel et al., 2004). Complete information on PPV geographical distribution is presented later in this chapter.