Peach latent mosaic viroid

The Complete Grape Growing System

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Figure 1 Secondary structures of potato spindle tuber and peach latent mosaic viroids. (A) A rod-like secondary structure for PSTVd is supported by a variety of physical studies as well as chemical and enzymatic mapping data. Boundaries of the terminal-left (Tl), pathogenicity, central conserved, variable and terminal-right (TR) domains are indicated by vertical lines. (B) Proposed lowest-free-energy structure of PLMVd. Predicted self-cleavage sites in the plus and minus strands are indicated by filled and open arrows, respectively. (Redrawn from Hernandez and Flores (1991) Proc. Natl. Acad. Sci. USA 89: 3711.)

Peach Latent Mosaic

Figure 2 Consensus phylogenetic tree containing 22 viroids, viroid-like satellite RNAs and the viroid-like domain of hepatitis delta virus RNA. ASBVd has been taken as outgroup. ***, Group monophyletlc in all 1000 bootstrap replicates;monophyletic in more than 99%;in more than 95%; +, in more than 90%; and - , in more than 80% of all replicates. From ASBVd to the left of the figure groups are considered as being within the viroid family, and from ASBVd to the right (including the viroid-like domain of HDV RNA) as within the satellite family. For example, satellite tobacco ringspot virus (sTRSV) and satellite Arabis mosaic virus (sArMV) (satellite family) or CCCVd, CTiVd and HLVd (viroid family) conformed to two well-defined monophyletic groups in all bootstrap replicates. G1 BVd, grapevine viroid 1B; LTSV, Lucerne transient streak virus; ScMoV, subterranean clover mottle virus; SNMV, Solanum nodiflorum mosaic virus; VTMoV, velvet tobacco mottle virus. Other abbreviations as in Table 1. (From Elena SF et a/(1991) Proc. Natl. Acad. Sci. USA 88: 5631, with permission.)

Figure 2 Consensus phylogenetic tree containing 22 viroids, viroid-like satellite RNAs and the viroid-like domain of hepatitis delta virus RNA. ASBVd has been taken as outgroup. ***, Group monophyletlc in all 1000 bootstrap replicates;monophyletic in more than 99%;in more than 95%; +, in more than 90%; and - , in more than 80% of all replicates. From ASBVd to the left of the figure groups are considered as being within the viroid family, and from ASBVd to the right (including the viroid-like domain of HDV RNA) as within the satellite family. For example, satellite tobacco ringspot virus (sTRSV) and satellite Arabis mosaic virus (sArMV) (satellite family) or CCCVd, CTiVd and HLVd (viroid family) conformed to two well-defined monophyletic groups in all bootstrap replicates. G1 BVd, grapevine viroid 1B; LTSV, Lucerne transient streak virus; ScMoV, subterranean clover mottle virus; SNMV, Solanum nodiflorum mosaic virus; VTMoV, velvet tobacco mottle virus. Other abbreviations as in Table 1. (From Elena SF et a/(1991) Proc. Natl. Acad. Sci. USA 88: 5631, with permission.)

to support ASBVd replication. HSVd has a particularly wide host range which includes several herbaceous species as well as woody perennials (e.g. grapes, citrus and various Prunus spp.). Many natural hosts of viroids are either vegetatively propagated crops, such as potato and chrysanthemum, or those that are subjected to repeated grafting or pruning operations. PSTVd, ASBVd and CbVd can all be vertically transmitted through pollen and/or true seed, but the significance of this mode of transmission in the natural spread of disease is unclear. PSTVd can be encapsidated by potato leafroll luteovirus (PLRV) as well as velvet tobacco mottle sobemovirus, and epidemiological surveys suggest that PLRV can facilitate viroid spread under field conditions.

Commonly used techniques for the experimental transmission of viroids include the standard leaf abrasion methods developed for use with conventional viruses, various 'razor slashing' methods in which phloem tissue in the stem or petiole is inoculated via cuts made with a razor blade previously dipped into the inoculum, and, in the case of CCCVd, high-pressure injection into folded apical leaves. PSTVd and HSVd have also been experimentally transmitted by 'Agroinoculation', a technique in which a modified Agrobacterium tumefaciens Ti plasmid is used to introduce full-length viroid cDNA into the potential host cell. In both cases, Agro-inoculation was able to overcome a marked host resistance to mechanical inoculation. Identification of the molecular mechanism(s) which determine host range remains an important research goal.

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