Detection of tobamoviruses on Lycopersicon esculentum seed by local lesion assay on Nicotiana tabacum plants

摘要

Local lesion assay (indexing) with Nico-tiana tabacum 'Xanthi NN' resistant plants was evaluated as a detection method for infectious tobamoviruses on tomato (Lyco-persicon esculentum) seed in a comparative test between nine laboratories, organized bythe International Seed Health Initiative Vegetable group (ISHI-Veg). Two naturally infected seed lots with medium and high infection levels, one virus-free seed lot and two infection levels of reference material (RM) were used. Subsamples of the seed lots and RM samples were distributed to laboratories who inoculated their extracts onto the leaf surface of two assay plants. For each combination of (sub)sample x plant x leaf, the number of necrotic local lesions was recorded 5-7 days post-inoculation under specific incubation conditions. No false positives were recorded, and most laboratories were able to detect the expected number of positive seed subsamples and RM samples, and to distinguish between the various infection levels. The growth stage of the tobacco assay plants and the incubation temperature were found to be critical factors for the detection of positive seed and RM samples. The local lesion assay was found to be repeatable and reproducible for both seed subsamples and RM samples. The use of a known infected seed sample or a reference material sample is indispensable for the validation of the results. The local lesion assay with Nicotiana plants resistant to tobamoviruses is considered a reliable detection method of infectious tobamoviruses on tomato seed and is highly recommended in routine tomato seed testing.