LONDON (Reuters)
- Growing different rice varieties together in one field increases
the crops' resistance to disease and improves yields, scientists
said in the journal Nature on Wednesday.
``Disease-susceptible
rice varieties planted in mixtures with resistant varieties had
89 percent greater yield and blast (a fungal disease) was 94 percent
less severe than when they were grown in a monoculture,'' the
scientists, who conducted a study in Yunnan province, China, said
in the journal.
The experiment
showed that growing different varieties of the same species of
crops in the same field -- a common feature of less developed
agriculture -- was an ecological alternative to pesticides, the
scientists said.
``The experiment
was so successful that fungicidal sprays were no longer applied
by the end of the two-year program,'' the scientists from China,
the Philippines and the United States said.
Lead scientist
Youyong Zhu suggested disease severity was reduced by increasing
the distance between plants of the same type -- which would be
susceptible to the same disease.
In addition
the mixture of crops engendered physical conditions which were
less suitable to the development of blast.
In some cases
'induced resistance' may have reduced the amount of plant tissue
suffering from rice blast, the scientists added. Induced resistance
occurs when a plant comes into contact with a disease which cannot
infect it but triggers its resistance response, preparing it to
fight off other diseases.
Monoculture
Problematic
Monoculture,
which is the dominant form of agriculture at present, is convenient
but problematic because it means all the plants in a field are
identical and susceptible to the same disease, scientist Martin
Wolfe said in another article.
Until now
the answer has been to breed disease resistant plants and use
fungicides. Unfortunately new fungicide resistant disease varieties
and microbes that can overcome resistant plants keep developing.
Wolfe suggested
that the mixture approach was not used more widely because farmers
were worried about product quality and the difficulty of harvesting
mixed varieties relative to pure varieties. These problems evaporated
in practice, he added.
``The mixture
approach represents a simple ecological way of dealing with disease
while maintaining production from high yielding varieties,'' Wolfe
told Reuters.
But the scientists,
who persuaded thousands of farmers in Yunnan province to participate
in the experiments, warned against a wholesale return to ancient
forms of agriculture.
``The current
world population of over six billion does not allow us to return
to agricultural production practices of the past. Rather, we need
to maintain the benefits of modern agriculture while addressing
its drawbacks,'' Zhu said.
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