Molecular characterization of PPV isolates from Egypt

Sharka, caused by Plum pox virus (PPV), is the most dangerous disease of stone fruit trees, reducing fruit quality and yield. PPV is easily transmitted by aphids and by vegetative multiplication, so, despite the considerable efforts made in many countries, Sharka has been reported in all the most important Prunus cultivation areas. No curative actions exist against Sharka and also the aphids vectors control is nearly ineffective. Control of PPV is essentially based on the early identification and elimination of the infected trees in field, and on the use of resistant germplasm . PPV in Egypt has been reported since 1987 and the well characterized strain El Amar has been so far identified only in that country on apricot plants. During 2009 season 100 samples from peach , apricot and plum symptomatic plants are been collected from orchards and nurseries in Alexandria governorate and then tested using both serological (ELISA) and molecular (RT-PCR) methods. Sixteen and 20 samples resulted infected, respectively, by DASI-ELISA test using the PPV universal monoclonal antibody 5B and by RT-PCR analysis using primers pair P1/P2. Results obtained show, within collected samples, high incidence of PPV infection on plum samples (50%) compared with incidence of 17% and 13% obtained from apricot and peach plants analyses, respectively. The last 593 nucleotides at 3’ end of PPV RNA, including portion of the coat protein gene and the complete 3’ untranslated region, are been amplified and sequenced from all infected samples. According to nucleotide sequence analysis all PPV isolates investigated in the present work, are been classified into the Dideron strain. High sequence identity, ranging from 98.3% to 100%, has been observed within all Egyptian isolates and no relationships between host species and sequence identity are been observed. All Egyptian accessions showed higher phylogenetic distance against the recombinant isolate “Serbia-MI” from Serbia and Montenegro (92.6% to 93.8% of sequence identity), against PPV-Marcus isolates (93.9% to 95.4%) and against PPV-El Amar isolates (92.9% to 94.1%). The higher sequence identity has been detected against one PPV-D East-European isolates from Belarus (99.2% to 99.7%) and against PPV-D isolates from USA (98.0% to 99.5%), Chile (98.0% to 99.3%) and Germany (97.5% to 99.5%). Our results show high incidence of PPV-D infected plants on orchards and nurseries in the Alexandria governorate. Presence of Dideron strain, considered the non-epidemic strain of PPV due its low efficiency on aphid-transmission, suggest a large diffusion of PPV-infected material used for plant propagation