TO SAVE their crops from rampaging bacteria, farmers in the American
Southwest have turned to the microbes鈥� natural enemies鈥攙iruses known as
bacteriophages.
Phages have long been used to battle bacteria that cause human disease,
particularly in Russia. In the agricultural world, however, farmers tried and
abandoned phages during the 1940s, largely because disease-causing bacteria
became resistant to them.
But Lee Jackson, president of AgriPhi in Logan, Utah, believes he has now
found a way round this. 鈥淲hen you start treating crops with one curative you get
resistant mutants,鈥� he says. 鈥淲hat makes my process different is that I have a
way of circumventing resistance.鈥�
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At the moment, there are two main ways to fight bacterial diseases in
plants鈥攁ntibiotics and copper compounds. But these methods have
disadvantages. Bacteria can become resistant to both treatments, and both can
also kill helpful soil microorganisms. And if copper compounds are applied too
heavily they can harm plant growth.
Using phages should be easier. The viruses are harmless to humans and tend to
target specific bacteria rather than kill indiscriminately. The phages are mixed
in a liquid and sprayed onto the field. They鈥檙e sucked up by the root systems of
the plants, and eventually infect the bacteria causing the disease.
To avoid resistance developing, Jackson cultures the bacteria that cause the
diseases, including resistant strains. He then screens phages until he finds
varieties that infect the resistant bacteria as well. He also mixes several
different phage varieties in one product, so that a bacterium that resists one
will probably be infected by another.
Jackson has found phages that fight the leaf spot caused by the bacterium
Xanthomonas campestris. He is experimenting on tomatoes and bell
peppers, and thinks the same method could work with other plants and
diseases.
According to an unpublished study by Jeffrey Jones, a plant pathologist at
the University of Florida in Gainesville, infected tomatoes treated with the
phage had a 25 per cent higher yield than tomatoes treated with a copper
compound.
Jackson鈥檚 colleague Brent Harbaugh 鈥攁nother University of Florida plant
pathologist鈥攊s trying a method similar to Jackson鈥檚 to fight a geranium
blight caused by Xanthomonas campestiis. 鈥淲e think it鈥檚 the right time
to look at this method,鈥� he says.