| 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.
|
