SEASONS OF THE GARDEN

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by Greg and Pat Williams

Vaccinate Your Plants!

Wouldn't it be great if you could somehow immunize your plants against diseases, just as people can be vaccinated against polio, tetanus, and so forth? Well, recent research has shown that plant immunization is indeed feasible. Plant pathologists at the University of Kentucky have injected certain compounds into potato, green bean, cucumber, watermelon, and other crop plants, giving them immunity to various bacterial, fungal, and viral diseases for up to six weeks!

The immunizing compounds (in particular, beta glucans) apparently speed and strengthen the plant's own generalized immune responses. This goes along with the theory that disease resistance is largely the ability to quickly recognize and respond to pathogens rather than a matter of having special "antidisease" genes.

Currently, the immunizing compounds are most often injected into crops . . . but they have been successfully sprayed on some (for example, cucumbers). And the Kentucky researchers are even working toward seed inoculations that would produce immunized plants without the need for in-garden treatments.

Unfortunately, immunization is not passed on genetically to subsequent generations, so the procedure must be repeated each season. On the other hand, a bit of tissue from a treated plant can be grafted on a nontreated one of the same species to confer immunity on that second plant. And the six-week resistance period can be extended for as long as the plant lives by occasionally challenging the immune system with pathogens (which stimulate a "booster" response).

Horticulturists at several other institutions besides the University of Kentucky are working on plant vaccinations. In fact, a recent report by the Weyerhaeuser Company claims that perennials such as apple, pear, prune, and coffee trees have been protected for up to three months with immunizations.

The technique is still experimental, but the results to date are extremely promising. Immunization has an almost unlimited potential for controlling plant diseases. And in general, the vaccination compounds being tested are derived from natural products.

How long will it be before such treatments become commercially available? We don't know, of course, but suspect that in only a few years you will be able to buy immunized seeds or immunizing sprays for your own garden.

Research Briefs

Watch out for ZYMV! If you grow cucumbers, squash, melons, or pumpkins, your garden might be visited by zucchini yellow mosaic virus (ZYMV) — sooner than you'd like! The aphid-transmitted curcurbit virus reduces yields and results in misshapen, lumpy, discolored fruits (which, however, are perfectly safe to eat). ZYMV was first discovered in Italy in 1981. Now it has spread to much of the U.S., including Arizona, California, Connecticut, Florida, Minnesota, New Jersey, and New York. Researchers are searching for resistant cultivars, but in the meantime, we might have to learn to like ugly cucumbers!

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