Aviv Dombrovsky

By Aviv Dombrovsky and Elisheva Smith

Global seed trade contributed to development and improvement of world agriculture. An adverse effect of global seed trade is reflected in disease outbreaks in new growing areas, countries, and continents. Among the seed-borne viruses, Tobamovirus species are currently considered a peril for crop production around the world. The unique tobamoviral particles confer stability to the RNA genome and preserve their infectivity for years. High titer of Tobamovirus species accumulates in reproductive organs leading to viral particles adsorbed to seed coat, which potentially establish a primary infectious source. Tobamovirus-contaminated seeds show very low virus transmission in grow-out experiments as detected by enzyme-linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR) analysis. Interestingly, in situ immunofluorescence analysis of Cucumber green mottle mosaic virus (CGMMV) reveals that the perisperm-endosperm envelope (PEE) is contaminated as well by the Tobamovirus. Indeed, chemical seed disinfection treatments that affect primarily the seed coat surface are efficient for several Tobamovirus species but apparently do not prevent seed transmission of CGMMV to occur. Tobamovirus infection of the seed internal layers, which rarely includes the embryo, may partially follow the direct invasion pathway of Potyviruses such as Pea seed-borne mosaic virus (PSbMV) to pea embryo.

Part of the book: Seed Biology

By Elisheva Smith and Aviv Dombrovsky

In the recent years, disease spread of old and newly evolved tobamoviruses has occurred worldwide, affecting production of various vegetable and ornamental crops. The tobamoviruses are highly stable plant viruses that could cause severe disease symptoms. The well-known tobamovirus Cucumber green mottle mosaic virus (CGMMV) has recently caused severe damages in the cucumber, melon, and watermelon cucurbitaceous crops, worldwide. Similarly, a recent widespread of the newly identified tobamoviruses, Tomato mottle mosaic virus (ToMMV) and Tomato brown rugose fruit virus (ToBRFV), has reduced the solanaceous crop production. The primary route of tobamoviral infection is through mechanical means. These viruses adhere to agricultural facilities, contaminate the soil, infect seeds, and spread via beneficial pollinators and irrigation water. Mechanical plant injury suffices to initiate viral infection. Practicing hygiene by plant growers and in nurseries is currently the main strategy for mitigation of tobamoviral infection. Promoting the production of solanaceous vegetable crops genetically resistant to ToMMV and ToBRFV infection is a promising approach. However, CGMMV-resistant sources of cucurbitaceous vegetable crops are scarce. Conferring resistance to rootstocks and cross-protection strategies are newly implemented approaches that could alleviate tobamovirus disease spread in both solanaceous and cucurbitaceous crops.

Part of the book: Plant Diseases