In the early 1970s, Yutaka Arimoto, then a young
researcher at RIKEN, wondered why the invasion of
the citrus tree fungus Diaporthe citri followed the
seasons. Perhaps that cycle could be used to defeat
it, he thought.
Yutaka Arimoto at the RIKEN Innovation Center has developed a treatment against the tomato yellow leaf curl virus that prevents transmitters of the virus, the silverleaf whitefly, from pairing on tomato plant leaves. © 2016 Yutaka Arimoto, RIKEN Innovation Center
Having grown up on a farm, Arimoto had seen
firsthand the damage pests and diseases cause to
crops, but he also knew that many pesticides used to
prevent them were later taken out of use.
“Unexpected things can happen, and there is never a
guarantee that current testing methods are
infallible,” he says. “No chemical is 100 per cent
safe, but by selecting compounds that people have
been consuming for a long time without adverse
effects, we assume that there is a very small chance
of unexpected problems arising.”
Arimoto's resolution to search for environmentally
friendly products with antifungal properties
launched him into a career developing commercial
pesticides from edible chemicals, which he refers to
as SaFE (Safe and Friendly to the Environment)
pesticides. But the path has not always been easy.
Today, a growing community of organic farmers is
creating a demand for agricultural products that
ensure the productivity, health and safety of soils,
plants, animals and people.
When considering the seasonal advance of Diaporthe
citri, Arimoto wondered whether antifungal
substances produced in citrus tree stems dwindled
when the citrus was harvested, making it vulnerable
to attack.
His hunch proved right: he discovered that a
yellowish compound called hesperidin in the stem,
when mixed with other common household products such
as potassium bicarbonate and sodium bicarbonate,
killed the fungus. Further experiments on other
pathogens produced similar fungicidal results,
even—much to Arimoto’s surprise—when the mixtures
did not contain hesperidin.
The mixtures contained sodium bicarbonate, more
commonly known as baking powder and a standard
treatment for heartburn and indigestion. Its close
relative, potassium bicarbonate, is also a popular
food additive in fizzy drinks, chocolate and canned
milk. “It’s safe to say that it is very unlikely
that compounds that have been approved for use in
these ways will lead to environmental problems,”
Arimoto comments.
Solutions of sodium and potassium bicarbonates
turned out to be especially good at protecting
against powdery mildew, a fungal disease that
affects wheat, barley and grapes, among other
plants, and can decimate farmers’ yields by almost
half.
In 1982, after several years of testing and field
trials, Arimoto registered his first sprayable
pesticide containing sodium bicarbonate, branded
Noslan wettable powder. But just as the team was
about to launch their new product on the market,
disaster struck. “Harmful toxic effects were
reported in strawberries and we had to halt
development,” he says. Twelve years had passed since
Arimoto began investigating compounds for use in
agriculture, and he was yet to find a success.
Undeterred, Arimoto looked for ways to prevent the
sodium bicarbonate from crystallizing on plant
leaves. Eventually, he discovered an ingredient that
could encapsulate the sodium bicarbonate in higher
doses, so that only a tenth of the original solution
needed to be sprayed on plants. The surfactant is
also a common food emulsifier.
With the original Noslan research group disbanded,
Arimoto initiated discussions with a company
manufacturing potassium bicarbonate. In 1993,
Toagosei Co., Ltd launched the product Kaligreen,
and Arimoto watched as it began to fly off the
shelves. “It was a very moving experience,” recalls
Arimoto. “At first, I didn’t think we would do so
well, but we were inundated with so many orders that
production couldn’t keep up.”
Kaligreen has since been approved for sale in 15
countries and the list keeps growing. Soon after it
went on sale in the United States, a farmer growing
grapes for organic wine requested that the fungicide
be certified by the Organic Materials Review
Institute. It was listed in 1999.
Kaligreen was the first of seven SaFE products that
Arimoto’s team has launched. The list includes the
fungicides G-FINE and Harmomate, which also contain
sodium bicarbonate. In November 2015, a remedy
against a disastrous tomato virus was approved for
release. “Bemidetouch Emulsion has an intriguing
effect on the silverleaf whitefly,” explains Arimoto.
The silverleaf whitefly transmits the tomato yellow
leaf curl virus, which stunts the growth of tomato
plants, sometimes causing farmers to lose their
entire harvests.
Arimoto’s insect repellent contains a substance that
tricks the whitefly into thinking that a plant is
not the right species to parasitize. The male
whitefly usually mates by sending out signals that
lure female whiteflies to the same leaves.
Bemidetouch prevents this pairing by weakening the
male signal.
In 2011, Arimoto’s decades of research were
acknoledged when he received a national merit award
for his contributions to industry, academia and
government through the promotion of SaFE pesticides.
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