Recent studies on peach latent mosaic viroid and American peach mosaic
The EPPO A1 list originally had the entry 'peach mosaic (American)' which remains in Annex IV of EU Directive 77/93. This disease has never been well characterized and its pathogen has never been identified. In the 1980s, several cases of mosaic were intercepted in peach plants imported into France from North America. The pathogen was identified and named as peach latent mosaic viroid. It was noted that the pathogen was originally found only in American peach material and it was proposed that American peach mosaic could be caused by this viroid. In any case, EPPO chose to focus attention on the identified pathogen. The EPPO Secretariat now reviews recent advances concerning peach latent mosaic viroid (EPPO A1 quarantine pest) and American peach mosaic which are summarized below.
1) New detection methods are now available to detect peach latent mosaic viroid in peach material: polyacrylamide gel electrophoresis (Flores et al., 1990), PCR (Shamloul et al., 1995) and molecular hybridization (Ambrós et al., 1995).
2) The geographical distribution is wider than previously thought. By using RT-PCR, Shamloul et al. (1995) were able to show that the geographical distribution of peach latent viroid (PLMVd) appears to be much wider than previously reported. The viroid could be detected in germplasm material of peach from the following countries: Austria*, Brazil*, Italy, Japan, Nepal*, Pakistan*, Romania*, USA and former Yugoslavia*.
3) Relationships between peach latent mosaic, and diseases called peach mosaic disease in USA and Mexico, and peach yellow mosaic in Japan have been clarified. It must be recalled that the agents responsible for these similar diseases have been thought by European virologists to be the same. Shamloul et al. (1995) demonstrated however, that the agent of peach mosaic disease is not related to peach latent mosaic viroid. In addition, James and Howell (1993) found that the agent of peach mosaic disease reacted with monoclonal antibodies specific to cherry mottle leaf closterovirus, which suggested that these pathogens could be related, although they differ in some aspects of their biology. For example, cherry is a primary host of cherry mottle leaf closterovirus but is not a host for peach mosaic disease, and mite vectors although related are different (Eriophyes insidiosus is a vector of peach mosaic disease and E. inaequalis is a vector of cherry mottle leaf closterovirus (Oldfield et al., 1995)). Concerning the other disease, Ambrós et al. (1995) confirmed that the agent causing peach yellow mosaic disease in Japan is indeed peach latent mosaic viroid.
4) Micro-grafting can be a tool to eliminate peach latent mosaic viroid from peach material: Barba et al. (1995) found that in vitro micro-grafting can eliminate the viroid from infected peach plants. Apex (of 0.3-0.8 mm long) are taken from mother plants and grafted onto healthy seedlings grown in vitro. However, the method is not always successful and seems to be influenced by the peach cultivar. The authors felt that a combination of in vitro micrografting and temperature treatments could improve the results.
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* New records according to the EPPO Secretariat.
Sources
Ambrós, S.; Desvignes, J.C.; Llácer, G.; Flores, R. (1995) Peach latent mosaic and pear blister canker viroids: detection by molecular hybridization and relationships with specific maladies affecting peach and pear trees.
Acta Horticulturae, 386, 515-521.
Barba, M.; Cupidi, A.; Loreti, S. Faggioli, F.; Martino, L. (1995) In vitro micrografting: a technique to eliminate peach latent mosaic viroid from peach.
Acta Horticulturae, 386, 531-535.
Flores, R.; Hernández, C.; Desvignes, J.C.; Llácer, G. (1990) Some properties of the viroid inducing peach latent mosaic disease.
Research in Virology, 141, 109-118.
James, D.; Howell, W.E. (1993) Comparison of cherry mottle leaf virus and a virus associated with peach mosaic disease.
6th International Congress of Plant Pathology, Montréal, Quebec, Canada, p 304.
Oldfield, G.N.; Creamer, R.; Gispert, C.; Osorio, F.; Rodriguez, R.; Perrings, T.M. (1995) Incidence and distribution of peach mosaic and its vector, Eriophyes insidiosus (Acari: Eriophyidae) in Mexico.
Plant Disease, 79(2), 186-189.
Shamloul, A.M.; Minafra, A.; Hadidi, A.; Giunchedi, L.; Waterworth, H.E; Allam, E.K. (1995) Peach latent mosaic viroid: nucleotide sequence of an Italian isolate, sensitive detection using RT-PCR and geographic distribution.
Acta Horticulturae, 386, 522-530.