Multilocus sequence analysis reveals the genetic diversity of European fruit tree phytoplasmas and supports the existence of inter-species recombination.

The genetic diversity of three temperate fruit tree phytoplasmas 'Candidatus Phytoplasma prunorum', 'Ca. P. mali' and 'Ca. P. pyri' has been established by multilocus sequence analysis. Among the four genetic loci used, the genes imp and aceF distinguished 30 and 24 genotypes, respectively, and showed the highest variability. Percentage of substitution for imp ranged from 50 to 68 % according to species. Percentage of substitution varied between 9 and 12 % for aceF, whereas it was between 5 and 6 % for pnp and secY. In the case of 'Ca P. prunorum' the three most prevalent aceF genotypes were detected in both plants and insect vectors, confirming that the prevalent isolates are propagated by insects. The four isolates known to be hypo-virulent had the same aceF sequence, indicating a possible monophyletic origin. Haplotype network reconstructed by eBURST revealed that among the 34 haplotypes of 'Ca. P. prunorum', the four hypo-virulent isolates also grouped together in the same clade. Genotyping of some Spanish and Azerbaijanese 'Ca. P. pyri' isolates showed that they shared some alleles with 'Ca. P. prunorum', supporting for the first time to our knowledge, the existence of inter-species recombination between these two species.

Occurrence, Distribution, and Relative Incidence of Mosaic Viruses Infecting Field-Grown Melon in Spain.

The main areas for field-grown melon (Cucumis melo) production in Spain were surveyed for the occurrence and relative incidence of cucumber mosaic virus (CMV), papaya ringspot virus-watermelon strain (PRSV-W), watermelon mosaic virus-2 (WMV-2), and zucchini yellow mosaic virus (ZYMV) during the growing seasons of 1995 and 1996. Samples from 1,152 plants showing symptoms of virus infection were collected from commercial melon fields and analyzed by enzyme-linked immunosorbent assay (ELISA). CMV and WMV-2 were the most frequently found viruses, both by the number of locations and by their incidence in each location. In contrast, PRSV-W and ZYMV were detected in fewer sites and at lower incidences. PRSV-W was not found in 1996. In 79% of the samples, only one virus was detected; 15% of the samples were doubly infected. Both the incidence of plants showing symptoms of viral infection and the relative incidence of each of the four viruses varied according to the region, while the main trends of virus distribution were similar for 1995 and 1996.