Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd) are known to naturally infect stone fruits, but their contemporary presence in peach trees has been reported only recently (3). During a field validation of detection methods developed for sanitary screening of propagation material, PLMVd and HSVd, alone or in mixed infections, were detected in peach trees grown in the trial orchard of the Czech University of Agriculture in Prague. Leaf samples were collected in September 2002 from symptomless trees of peach cultivars imported from the United States (cvs. Sunhaven, Redhaven, Fairhaven, Cresthaven, Dixired, Halehaven, and NJC 103), Slovakia (cv. Luna), and a tree of Chinese wild peach, Prunus davidiana, and analyzed by reverse transcription-polymerase chain reaction (RT-PCR). PLMVd cDNA was amplified as previously reported (2) or by using two sets of primer pairs designed to amplify partial cDNAs, one reverse primer R: GTTTCTACGG CGGTACCTGA, complementary to the nucleotide positions 204 to 223 and forward primers F1: CGTATCTCAACGCCTCATCA, homologous to the positions 109 to 128, and F2: CTGCAGTTCCCGCTAGAAAG, homologous to the positions 15 to 34 of PLMVd reference sequence (2). The two pairs using the R sequence produced the expected size PCR products of 115 and 209 bp, respectively. RT-PCR for HSVd detection was performed as reported (1). The same total RNA preparations were also analyzed by molecular hybridization with nonisotopic riboprobes specific for each viroid. With minor exceptions, both methods gave similar results. Of 66 tested trees, 5 were infected with PLMVd, 46 were infected with PLMVd and HSVd, and 15 were free of both viroids. Viroid free plants included cvs. Luna, Cresthaven, Dixired, and Halehaven and the species P. davidiana. The high number of infections by both viroids was unexpected because mixed infections are generally rare (3). Most likely, mixed infections occurred during field manipulations and propagation of infected materials. To our knowledge, this is the first report of PLMVd in the Czech Republic. Although further investigations are needed to ascertain the spread of stone fruit viroids in the Czech Republic, our results also report an unusually high incidence of mixed infections of peach trees in this country. These results stress the need for a certification program to help control the spread of stone fruit viroids in the Czech Republic.
References: (1) K. Amari et al. J. Gen. Virol. 82:953, 2001. (2) A. M. Shamloul et al. Acta Hort. 386:522, 1995. (3) M. Tessitori et al. Plant Dis. 86:329, 2001.
