Causal agent of sharka disease: new and emerging events associated with Plum pox virus characterization

Complete genome sequence of a novel Plum pox virus strain W isolate determined by 454 pyrosequencing

The near-complete (99.7 %) genome sequence of a novel Russian Plum pox virus (PPV) isolate Pk, belonging to the strain Winona (W), has been determined by 454 pyrosequencing with the exception of the thirty-one 5'-terminal nucleotides. This region was amplified using 5'RACE kit and sequenced by the Sanger method. Genomic RNA released from immunocaptured PPV particles was employed for generation of cDNA library using TransPlex Whole transcriptome amplification kit (WTA2, Sigma-Aldrich). The entire Pk genome has identity level of 92.8-94.5 % when compared to the complete nucleotide sequences of other PPV-W isolates (W3174, LV-141pl, LV-145bt, and UKR 44189), confirming a high degree of variability within the PPV-W strain. The isolates Pk and LV-141pl are most closely related. The Pk has been found in a wild plum (Prunus domestica) in a new region of Russia indicating widespread dissemination of the PPV-W strain in the European part of the former USSR.

Putative recombination events and evolutionary history of five economically important viruses of fruit trees based on coat protein-encoding gene sequence analysis

To enhance the knowledge of recombination as an evolutionary process, 267 accessions retrieved from GenBank were investigated, all belonging to five economically important viruses infecting fruit crops (Plum pox, Apple chlorotic leaf spot, Apple mosaic, Prune dwarf, and Prunus necrotic ringspot viruses). Putative recombinational events were detected in the coat protein (CP)-encoding gene using RECCO and RDP version 3.31beta algorithms. Based on RECCO results, all five viruses were shown to contain potential recombination signals in the CP gene. Reconstructed trees with modified topologies were proposed. Furthermore, RECCO performed better than the RDP package in detecting recombination events and exhibiting their evolution rate along the sequences of the five viruses. RDP, however, provided the possible major and minor parents of the recombinants. Thus, the two methods should be considered complementary.

Emerging Plant Viruses: a Diversity of Mechanisms and Opportunities

Although emerging plant viruses receive much less publicity than their animal- or human-infecting cousins, they pose a serious threat to worldwide agricultural production. These viruses can be new (i.e., not previously known) or already known; however, they share the common characteristic of occupying and spreading within new niches. Factors driving the emergence of plant viruses include genetic variability in the virus, changes in agricultural practices, increases in the population and/or distribution of insect vectors and long-distance transport of plant materials. In recent years, individual as well as entire groups of viruses have emerged, and this has involved a variety of mechanism(s), depending on the virus and the environment. Here, we will discuss some of these viruses, and highlight the mechanisms that have mediated their emergence. Special emphasis is placed upon the whiteflytransmitted geminiviruses (begomoviruses) and the thrips-transmitted tosposviruses, which have emerged as major threats to crop production throughout the world. Other examples include the recent emergence of novel viruslike agents, the acquisition and role of satellite DNA or RNA molecules in emergence of plant viruses, and cases where emerging viruses have had only a transient impact. It seems clear that global movement of plant materials, expansion of agriculture and large-scale monoculture will continue to favor emergence of plant viruses. However, improved diagnostics should allow for rapid identification of emerging viruses and better understanding of viral biology. This information can be used in the development of effective management strategies, which will hopefully minimize impact on agricultural production.

Assessment of the diversity and dynamics of Plum pox virus and aphid populations in transgenic European plums under Mediterranean conditions

The molecular variability of Plum pox virus (PPV) populations was compared in transgenic European plums (Prunus domestica L.) carrying the coat protein (CP) gene of PPV and non-transgenic plums in an experimental orchard in Valencia, Spain. A major objective of this study was to detect recombination between PPV CP transgene transcripts and infecting PPV RNA. Additionally, we assessed the number and species of PPV aphid vectors that visited transgenic and non-transgenic plum trees. Test trees consisted of five different P. domestica transgenic lines, i.e. the PPV-resistant C5 'HoneySweet' line and the PPV-susceptible C4, C6, PT6 and PT23 lines, and non-transgenic P. domestica and P. salicina Lind trees. No significant difference in the genetic diversity of PPV populations infecting transgenic and conventional plums was detected, in particular no recombinant between transgene transcripts and incoming viral RNA was found at detectable levels. Also, no significant difference was detected in aphid populations, including viruliferous individuals, that visited transgenic and conventional plums. Our data indicate that PPV-CP transgenic European plums exposed to natural PPV infection over an 8 year period caused limited, if any, risk beyond the cultivation of conventional plums under Mediterranean conditions in terms of the emergence of recombinant PPV and diversity of PPV and aphid populations.