Recent emergence of seed-borne viruses and viroids on tomato, seed health tests and their implications in global seed trade

Authors: Ling, Kai-Shu

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2020
Publication Date: 3/1/2021
Citation: Recent emergence of seed-borne viruses and viroids on tomato, seed health tests and their implications in global seed trade Acta Hortic. 1316: 127-134. in ISHS 2021. DOI 10.17660/ActaHortic.2021.1316.18 Proc. VI International Symposium on Tomato Diseases Eds.: L. Kenyon et al.
DOI: https://doi.org/10.17660/ActaHortic.2021.1316.18

Interpretive Summary:

Technical Abstract: Tomato is one of the most important and widely grown vegetables in the world. With an increasing trend in off-shore hybrid seed production and global seed trade activity, the risk of introducing a seed-borne pathogen from a different country with seed as a pathway is high if a rigorous seed health test program is not implemented. For some common seed-borne viruses, such as tobacco mosaic virus (TMV), tomato mosaic virus (ToMV) and pepino mosaic virus (PepMV), standard seed health assay methods are available. For those emerging seed-borne viruses and viroids, including tomato mottle mosaic virus (ToMMV), tomato brown rugose fruit virus (ToBRFV), potato spindle tuber viroid (PSTVd) and several other tomato-infecting pospiviroids, there is an urgent need to understand the mechanism of seed transmissibility and to develop appropriate seed health assays. To achieve a meaningful risk assessment, a sensitive lab test would need to be complemented with an appropriate bioassay. This is especially important for those seed lots that are treated. Recent outbreaks of ToBRFV and pospiviroids on greenhouse tomato in the U.S. and Mexico, highlighting the importance of including some emerging viruses and viroids in seed health test. For seed-borne viruses, the most common technique for seed health test is a serological method (e.g., ELISA) followed by a bioassay to confirm the infectivity of virus particles in a seed lot. For tomato-infecting pospiviroids, with multiple species and greater genetic diversity, there is still a debate as to whether all known tomato-infecting pospiviroids or just some of them should be included. For those seed health assay methods that are sequence-based techniques, genetic variability should be considered in designing the primers that will offer a sensitive detection, with no cross reaction to other related species. I will address these challenges and offer some solutions in developing a meaningful seed health program.