Plant viruses share many of the characteristics of those that infect animals, though they do not cross infect (plant viruses only infect plants). Viruses are extremely minute and consist of a protein coat and a core of nucleic acid. They have no means of self-dispersal, but rely on various vectors to transmit them from infected to healthy plants. Once viruses penetrate into the plant cells they take over the cells’ nucleic acid and protein synthesis systems and hijack them to produce more virus. They then require another vector to feed on the infected tissue and carry them to a new host.
- CMV, LSV and TBV are vectored by aphids
- ArMV and TRV are vectored by soil inhabiting nematodes
- TNV is vectored by the microscopic fungal root pathogen Olpidium brassicae
Other viruses may be vectored by other insects, mites or by mechanical transmission on pruning tools.
Tulip breaking virus (TBV) had an important role in 'tulipomania', which affected the Netherlands in the seventeenth century. The break patterns in affected bulbs were highly prized and sellers commanded huge prices. Unfortunately, the effect was often not stable and affected bulbs did not repeat the patterns reliably in future years. Tulip varieties with these patterns are available today, but the breaks result from stable genetic mutation and not virus infection. The English florists' tulips are an exception, in which the flower breaks still result from infection with TBV and are remarkably stable, although these plants are seldom available for sale.