**Author details**

[34] and the endosperm in *Solanaceae* seeds [4, 35]. The second limitation of the ELISA method, which is false-positive results, may occur in instances that show lack of correlation between the ELISA results and biological significance. The possibility of obtaining false-positive or false-negative ELISA results may lead to situations in which growers purchase treated seed lots that are contaminated. Since the ELISA assay detects only the CP subunit, it is not possible to draw a direct link between ELISA results and the status of the viral particles or the degree of infectivity de facto. It is a major obstacle even when more sensitive molecular-based methods such as reverse transcription polymerase chain reaction (RT-PCR) [3, 160, 161] or quantitative real-time polymerase chain reaction (qRT-PCR) [162–164] are applied, which detect amplified partial genome fragments. Therefore, especially when dealing with treated/disinfected commercial seed lots, the preferable scenario is to validate the ELISA-positive seed subsamples in biological assays on susceptible indicator plants in order to ensure the infectivity status of the

The contribution of seed transmission to viral spread may be significant even under conditions of low seed-to-seedling transmission rate. The rapid spread of tobamoviruses by any mechanical contacts is reflected in the spread of the disease especially in plants that are grown trellised in protected structures. This mechanical virus spread may occur when handling seeds and transplanting seedlings. Furthermore, the modern monoculture agriculture contributes to virus buildup, preservation, and spread to new susceptible host plants which increase viral copy number leading to higher viral load in the growing area. Tobamoviruses contaminate both the seed coat and the PEE or the endosperm. The mechanism of *Tobamovirus* transmission in the seed is not quite clear, but it may follow the path suggested for the *Potyvirus* PSbMV in pea seeds. Seeds have regulatory mechanisms that may limit virus transmission, and domi-

tobamoviruses have recently been spread, and new approaches for conferring resistance to cultivars against tobamoviruses are in demand. The CRISPR-Cas9 methodology offers exciting prospects and provides an alternative approach to conventional breeding for the acquisition of resistance to viruses. Hopefully, in the near future, it will be applied to *Tobamovirus*

We would like to thank Dr. Nadav Elad from the Electron Microscopy Unit, Departments of Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel, for the great TEM analysis and to Victoria Reingold for the in situ immunofluorescence data of CGMMV. This work was supported by the Chief Scientist, Israel Ministry of Agriculture, and the Plant Production and Marketing Board for CGMMV initiative project number 132–1740 and *Tm-22*

and L<sup>4</sup>

resistance-breaking

nant resistance genes block virus transmission. However, *Tm-22*

Tobamo breaker in tomato plants, initiative project number 261–1159.

tested seed lot before marketing or sowing.

**11. Conclusions**

248 Advances in Seed Biology

species in imported crops.

**Acknowledgements**

Aviv Dombrovsky\* and Elisheva Smith

\*Address all correspondence to: aviv@volcani.agri.gov.il

Department of Plant Pathology, ARO, The Volcani Center, Rishon LeZion, Israel
