Characterization of two isolates of Prunus necrotic ringspot virus (PNRSV) from peach and apricot in Egypt

Two isolates of PNRSV were isolated from peach and apricot trees at the Experimental Station of the Faculty of Agriculture, Cairo Univer sity, Giza, Egypt. The peach isolate of PNRSV (PNRSV-PF) was differentiated from the apricot isol ate (PNRSV-AP) by ten differential host species. Both isolates were purified successfully w ith the electro-elution technique. Both isolates had A max and A min at 260 and 240 nm respectively. The A260/280 ratios were 1.55 and 1.6 0 for the AP and the PF isolates, respectively. Electron mic roscopy examination showed spherical virions with ca 27-29 nm in diameter. Both isolates had mo lecular weight of coat protein subunits of 29 kDa, determined by polyacrylamide gel electrophores is (SDS-PAGE). Antisera raised against the two isolates detected their counter antigens in pea ch and apricot trees. Both antisera cross reacted with their homologous and heterologous antigens in dot blot immunoassay (DBIA) and agar-double diffusion (ADD) tests. The two virus isolates appea red to belong to the same sero-group and represent two different pathotypes. PNRSV-AP varie d in sero-grouping of that of beet necrotic ringspot ilarvirus, a tentative isolate of PNRSV, w hen examined in ADD test. Indirect ELISA showed that 64.2 % of 210 tested apricot trees were infected, while 150-inspected peach trees showed 29.5 % infection. Four sets of primers were used to amplify both movement protein (MP) and coat protein (CP) genes of the two Egyptian iso lates of PNRSV isolated from apricot and peach trees. Amplicons of the correct size (~ 894 bp) fo r the MP gene and (~ 704 bp) for the CP gene were obtained from the two examined isolates of PNR SV. Nested PCR using specific primers for both the MP and the CP genes confirmed the authenti city of the PCR amplified products. RT-PCR detected successfully the presence of PNRSV in the pollen grains of infected apricot and peach trees. Nucleotide sequences of the MP genes of the two isolates were revised by the GenBank and given the accession # EU100388 for the peach isolate and EU106649 for apr icot isolate. Phylogenetic analysis of RNA 3-MP showed ca 65 % si milarity between PNRSV-AP and PNRSV- PF; indicating that the two isolates of PNRSV are d istantly related. The relatedness between the two isolates and other PNRSV isolates is discussed.