SUMMARY Sixteen isolates of Plum pox virus (PPV) were collect- ed during a survey in the Egyptian areas of Sinro and Apoxa (El Fayoum) and El Amar (Nile Delta). All iso- lates reacted with the universal PPV monoclonal anti- body MAb 5B and were identified as PPV strain EA by phylogenetic analysis of the full-length sequence of the coat protein (CP) gene. This classification was con- firmed by detection with the strain-specific MAb EA24, except for an isolate denoted APR 50. Detailed analysis of the CP amino acid sequence of the EA isolates and epitope mapping revealed that histidine at amino acid position 65 of the CP sequence is an essential compo- nent of the epitope required for MAb EA24 recogni- tion. APR 50 has an arginine substitution at this posi- tion. Five EA serogroups were identified, serogroup I being the prevailing one with 10 of the 14 isolates char- acterized. Moderate serological and relatively high ge- netic diversity was observed among isolates of PPV-EA. The most variable isolate, APR 48, contained a deletion of 33 nucleotides at the 5’ terminus of the CP gene. The relatively high genetic diversity of PPV-EA suggests that it is not a recent introduction. Key words: Plum pox virus, sharka, El Amar, mono- clonal antibodies, RT-PCR, sequence analysis, epitope mapping. INTRODUCTION Sharka or plum pox, the most important disease af- fecting global production of Prunus spp, induces crop lossess as high as 95-100% (Németh, 1986; Garcia and * Present address: Istituto di Virologia Vegetale, CNR, Strada delle Cacce 73, 10135 Torino, Italy ** Present address: Dipartimento Territorio e Sistemi Agro-Forestali – Pa- tologia Vegetale, Università degli Studi di Padova, Agripolis, Viale dell’Uni- versità 16, 35020 Legnaro (PD), Italy Corresponding author: S. Matic Fax: +39.011.343809 E-mail: s.matic@ivv.cnr.it Cambra, 2007). It was first detected in Bulgaria in 1918 (Atanasoff, 1932), and is now found in at least 41 coun- tries, in five (Africa, Asia, Europe, North and South America) of the seven continents (Garcia and Cambra, 2007). Sharka is caused by Plum pox virus (PPV), a member of the genus Potyvirus, the largest and most economically important group of plant viruses (Shukla et al., 1991). The virus displays genetic, serological, and biological diversity (Marénaud and Massonie, 1977; Candresse et al., 1998; Bousalem et al., 2000; Myrta et al., 2001). The genome of PPV is a positive sense single- stranded RNA ca. 10 kb in size, encoding a polyprotein of 355.5 kDa that is cleaved post-translationally into 10 functional proteins (Riechmann et al., 1989; Shukla et al., 1991; Garcia et al., 1994), one of which is the genome-linked protein found at the 5’ terminus. The genome contains a 5’ and a 3’ non-coding region, and a poly(A) tail at the 3’ end (Garcia et al., 1994; Riech- mann et al., 1989). There are seven recognized strains of PPV denoted C, D, EA, M, Rec, T, and W (James and Glasa, 2006; Myrta et al., 2006; Ulubas Serçe et al., 2009). The strains are serologically distinct, and isolates of each strain can be identified by serology-based and/or by nucleic acid-based techniques. PPV strains differ in pathogenicity, host range, aphid transmissibility, and geographical distribu- tion. Isolates of the strain PPV-EA are found only in Egypt (Wetzel et al., 1991a; Myrta et al., 2006). The Mediterranean basin countries account for more than 50% of the world’s apricot (Prunus armeniaca) pro- duction (Moustafa et al., 2001). The cultivated area of apricot in Egypt is about 15,585 ha with an approximate yearly production of 106,165 tons (Anonymous, 2008). In the past, apricot cultivation was based in the Nile Delta (in which El Amar village is located) and El Fayoum re- gions, but is now concentrated in new land reclaimed from the desert. There are many local apricot varieties grown in Egypt such as El Amar, Balady, Amal, and Hamawy, and also imported varieties such as Canino. Our study focused on the characterization of the serological and molecular diversity of Egyptian PPV iso- lates since limited information is available on the vari- ability of these isolates and only a few PPV-EA se- quences are available in GenBank. Journal of Plant Pathology (2011), 93 (2), 303-310 Edizioni ETS Pisa, 2011 303 SEROLOGICAL AND MOLECULAR CHARACTERIZATION OF ISOLATES OF PLUM POX VIRUS STRAIN EL AMAR TO BETTER UNDERSTAND ITS DIVERSITY, EVOLUTION, AND UNIQUE GEOGRAPHICAL DISTRIBUTION S. Matic 1* , I. Elmaghraby 2** , V. Law 3 , A. Varga 3 , C. Reed 3 , A. Myrta 4 and D. James 3 1 Dipartimento di Protezione delle Piante e Microbiologia Applicata, Università degli Studi “Aldo Moro” and Istituto di Virologia Vegetale, UOS Bari, Via Amendola 165/A, 70126 Bari, Italy 2 Istituto Agronomico Mediterraneo, Via Ceglie 9, 70010 Valenzano (BA), Italy 3 Centre for Plant Health, Canadian Food Inspection Agency, 8801 East Saanich Road, Sidney, British Columbia, Canada V8L 1H3 4 Certis Europe B.V., Via A. Guaragna 3, 21047 Saronno (VA), Italy