Vaccines for plants?

In 1892 a German physician, Richard Pfeiffer, believed he discovered the culprit that caused the Influenza Epidemic of 1889-90. An Infuenza bacillus became the focus of attention in the fight against the Spanish Influenza of 1918-19. Vaccines were being developed just as they had 100 years earlier for smallpox. Medicine had already conquered rabies, tetanus, anthrax and cholera before the new century. But they would prove ineffective and the Great Pandemic would simply fade away.

In 1933 an article “Failure of a Bacterial Vaccine...Against Influenza” announced the discovery of a new pathogen, a virus, Influenza A. Five years later Doctors Salk and Francis would develop the first vaccine for Influenza A and B. But the H1N1 virus has not faded away. It was believed to have caused the epidemics of 1848-9 and 1889-90. In my lifetime it has resurrected in 1957, 1968, and again in 2009. These pathogens are genetic strands looking for a way to replicate. Unlike bacterium which can reproduce outside or inside another living organism a virus can only replicate in a host living cell. For this reason viruses actually become less deadly as they mutate. Without a host their fate is in jeopardy as well.

Viruses are spread initially and primarily by mosquitoes, ticks, and sand-flies. When conditions for these arthropods are good they create an environment for the spread of these pathogens to plants, animals, and humans. Just like the mistakes of the past many plants problems have been attributed to bacterium or fungal disease, when, in fact, there are many viruses that can affect plants and threaten our food supply.

Many of these viruses in plants manifest as mosaics. Cucumber Mosaic Virus (CMV), zucchini (CYMV), and tobacco (TMV) are just a few of the predominate. TMV, in particular, hitchhikes on aphids and other insects; it affects many of the Solanaceae family, including tomatoes, peppers, and potatoes. Mosaics can show up as mottlings, variegations, mutilated leaves, and more. What is significant is these disfigurements are not caused by the virus but by the plants fighting off the virus. A plant’s own genetic material will recognize the intruder and try to cut off its path with its enzymes and other defense mechanisms, called the Argonaut complex. It is this shotgun approach that does damage, but plants can win in this process. Science, as in the study of viruses that affect humans, must realize the most effective and least destructive complex. The result is treatments such as vaccines. In plants they are sprayed or rubbed onto the foliage ( probably no needles).

In the landscape industry, we have had two recent incidents of viruses affecting planting material. In 1996 Hosta Virus X (HVX) was recognized. It is a sap to sap vehicle that spreads this pathogen. In the beginning many of the mutations to hostas were thought beautiful and desirable. But the degradation and spread by mere proximity and handling brought the problem to a head. Culling of affected plants, spacing of plants, and more recently testing for virus at plant production sources have all but eliminated the problem.

In 2011 the greenhouse growers were faced with Impatiens Necrotic Spot Virus (INSV). The result was a loss of cash crop for several years as growers sought out strains resistant to this virus. Noteworthy is the fact that many viruses in plants are actually passed on by seed.

Although genetic mapping is still relatively new it is beyond hopeful that science and medicine will be able to give us the tools to fight these pathogens and protect our food supply.