Epidemiology of sharka disease in France

Abstract

Plum pox virus was first detected in France in the 1960s. Both PPV-D and PPV-M strains are present but epidemics related to the PPV-M strain detected in the late 1980s are the most problematic. The two PPV strains have unequal distributions in peach and apricot orchards and different prevalences. More than 20 different aphid species have been identified as vectors of PPV but most of them do not colonize Prunus species. Thus, aphids involved in the spread of PPV in orchards are essentially visiting aphids. The main sources of inoculum for the vectors are leaves and fruits of infected stone-fruit trees. Spontaneous, wild and ornamental Prunus species such as Prunus dulcis , P. spinosa or P. pissardii are susceptible to PPV isolates found in France but their role as a reservoir in sharka epidemics is probably negligible. The disease spreads rapidly in orchards but the rate of progression may vary according to the identity of the PPV strain and the Prunus species. Analysis of spatial patterns of disease has shown that secondary spread by aphids frequently occurs over short distances in the orchards (aggregated patterns) but also that dissemination at longer distances (of several hundred metres) is a common event. PPV DiversityPlum pox virus (PPV) was first detected in France in the 1960s (Morvan, 1988), especially on apricot trees, where the disease was maintained at a very low incidence by control measures. A new phase in sharka epidemics began in the 1990s with the detection of infections which spread at an unusual rapidity in peach orchards .A survey was carried out in apricot and peach orchards in the years 1992-95 by the French Plant Protection Service jointly with INRA to characterize the diversity of PPV populations present in south-eastern France. 200 isolates were collected and characterised using electro-blot immunoassay (EBIA) and Restriction Fragment Length Polymorphism (RFLP) analysis targeting the coat protein gene. Sequencing of the 5 ′ -and 3 ′ ends of the CP gene was also carried out for a selected set of isolates (Dallot et al ., 1998). The majority of the collected isolates belonged to the two main PPV groups (PPV-D and PPV-M strains). A minority of isolates (10%) collected on peach trees showed an atypical electrophoretic mobility pattern but were classified as the PPV-D strain based on sequence properties. A more limited screening of PPV isolates was performed later on but did not provide evidence of the presence of strains of PPV other than PPV-M and PPV-D in France, nor of recombinant isolates Glasa et al ., 2002).The distribution of PPV-D and PPV-M isolates was clearly unequal on apricot and peach trees: 80% of PPV-M isolates being found on peach trees, whereas on apricot trees PPV-D isolates predominated although PPV-M isolates were also found (Dallot et al ., 1998). It is believed that such an uneven distribution reflects distinct epidemic potentialities of PPV strains as well as the historical background of sharka disease in France . Aphid speciesPPV is a non-persistently transmitted aphid-...

Assessment of the diversity and dynamics of Plum pox virus and aphid populations in transgenic European plums under Mediterranean conditions

“…A. spiraecola was the most probable significant vector of PPV in European and Japanese plums in the experimental orchard, as has been reported for Japanese plums in other Mediterranean Spanish Prunus growing areas (Cambra et al 2004;2006a). Results from other Mediterranean countries showed that A. gossypii is the most abundant aphid in apricot orchards in Spain and Greece (Avinent et al 1989(Avinent et al , 1991(Avinent et al , 1993Varveri et al 2004) and A. spiraecola is the predominant aphid species in apricot orchards in south-eastern France (Labonne and Dallot 2006) In non-Mediterranean climate areas, such as Pennsylvania (USA), the most abundant aphid species caught on peach trees were Rhopalosiphum maidis (Filch) and A. spiraecola. As R. maidis is unable to transmit Pennsylvanian isolates of PPV, A. spiraecola is also the most probable PPV vector in this region (Wallis et al 2005).…”

Sharka Epidemiology and Worldwide Management Strategies: Learning Lessons to Optimize Disease Control in Perennial Plants

“…Moreover, there are several conference reports of naturally infected weeds in Central and Eastern Europe (cited in 84); these reports are yet to be confirmed by molecular characterization. Finally, the role of herbaceous hosts in sharka epidemics, if any, should be negligible because their amount of foliage is very limited compared with that of adult prunus trees (72).…”

“…The mean number of nonpersistent virus particles inoculated to a host plant by an aphid has been estimated as between only 0.5 and 3.2 particles for Potato virus Y (genus Potyvirus) (90) and 1 to 2 particles for Cucumber mosaic virus (genus Cucumovirus) (5). In natural conditions, aphids passing through prunus orchards are the most efficient vectors of PPV (72,76; see sidebar Why Pesticides Generally Fail with Nonpersistent Viruses), with hundreds of thousands of aphids visiting a tree each year (73). Leaves and, to a lesser extent, fruits constitute sources of PPV for aphid-mediated transmission (49, 74).…”

Unfolding the secrets of plum pox virus: from epidemiology to genomics

“…For example, PPV-M is generally regarded as a very severe strain, while PPV-D is taken as relatively less epidemic in the western Mediterranean region. One of the reasons should be that natural hosts of PPV-M (peach, nectarine, possibly apricot) are much more economically important in this territory than plums hosting predominantly PPV-D (Labonne and Dallot, 2006).…”