Tomato spotted wilt and impatiens necrotic spot tospoviruses are not seed-transmitted
In reaction to the paper from Davino et al. (1994) concerning the possible transmission of tomato spotted wilt tospovirus (EPPO A2 quarantine pest) through seeds (EPPO RS 94/204), the EPPO Secretariat has been informed that during studies carried out in the Netherlands, seed transmission has never been found. Seed transmission was respectively studied on impatiens, sweet pepper and tomato for tomato spotted wilt virus, and on Cineraria and impatiens for impatiens necrotic spot virus. Seeds were harvested from infected plants and at least 400 seedlings per species were inspected and tested for the presence of these viruses. For none of these species, infected seedlings have been found.
In addition, the Dutch experts stressed that as TSWV is not found in the embryo of seeds, it indicates that seed transmission is not very probable. Although the virus can be present in the seed coat, infection of the embryo from this source is unlikely because of the low stability of the virus particles. In order to explain this discrepancy between the results obtained in Italy and Netherlands, the Dutch experts wondered whether the type of "virus-net" used in the experiment was adequate (mesh size should be 80 µm maximum to exclude thrips) and whether the presence of viruliferous pupae hidden in the soil was excluded.
It may also be noted that Annex II/A2 of EU Directive 77/93 prohibits host plants of TSWV intended for planting, seeds apparently included. EPPO has interpreted this as a mistake, when preparing the EPPO Summary of the EU Directive.
Sources
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EPPO Secretariat, 1994-12.
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