The Rural Voice, 1989-05, Page 22SEEDS
OF TH
FUTURE
What has been
done to protect
the genetic
diversity of our
crops while more
and more farmers
have turned to
monoculture and
the use of a narrow
spectrum of high -
yielding plants?
Plenty, but not
enough.
by Ian Wylie-Toal
20 THE RURAL VOICE
//
Don't put all your eggs into
one basket." Life being
what it is, there is a good
chance that the basket will get bumped
or dropped, and when it goes, all the
eggs will tumble with it.
Yet, for most of this century, world
agriculture has been putting more and
more of its "eggs," which in this case
are plants, into fewer and fewer
baskets.
The variety of crop plants has
shrunk considerably since the start of
agriculture some 10,000 years ago.
A mere eight crop plants now account
for three-quarters of all human nutri-
tion, and four of these — wheat, rice,
maize, and sorghum — account for
more than half of the calories
consumed by people.
More alarming is how much the
genetic diversity of these crops has
been reduced, raising fears of massive
crop losses and lowering the potential
for breeding higher -yielding plants to
feed an increasing human population.
Compare the condition of crop
plants when agriculture began. Early
farmers domesticated the plant species
they found nearby because these
plants were best suited to local grow-
ing conditions. Once a species had
been chosen as a food crop, farmers
would start selecting the types that
best suited their needs. Plants that
showed some disease resistance,
didn't fall over, or were easy to har-
vest were favoured. And because no
one variety or species was suitable for
all conditions, a mixture of plants was
seeded to ensure that some would
mature.
Dr. J. R. Harlan, writing about
"Our Vanishing Genetic Resources"
in 1975 (Science, vol. 188: 618), calls
the artificial selection pressure put on
these wild plants "intense." He
describes how the movement of plants
through human migration and trading
exposed crop plants to new conditions
and therefore new selective pressures,
further promoting genetic diversity.
According to Dr. Harlan, these so-
called "landraces" differed in their
reaction to diseases and pests, so no
pathogens could build up to epidemic
proportions because there were always
some resistant plants in the popula-
tion. He writes that landraces were
lower yielding but dependable, being
adapted to crude methods of land
preparation, seeding, weeding, and
harvesting. No matter what happened
in a given year, the farmer would get
something out of his field.
Most of this early crop evolution
took place in what are called Vavilov
centres, areas of the world recognized
by the Russian plant breeder and
geneticist N. I. Vavilov as the regions
in which the major food crops origin-
ated and flourished. These areas
correspond with the areas of earliest
human civilization, centring on the
advanced civilizations that arose in
Mexico, Peru, Egypt, Mesopotamia,
India, and China. These areas had the
weedy relatives and human habitation
that promoted the genetic expansion
of crop plants.
According to the authors of Gene
Banks and the World's Food (Donald
L. Plucknett et al.) this process of c -op
evolution continued throughout most
of human history, even into the col-
onial era. They say that the decline
of crop diversity began with the intro-
duction of modern plant breeding
methods. Plant breeders concentrated
on a restricted number of plants,
producing varieties that out -yielded
the landraces. Naturally enough,
farmers discarded the old in favour of
the new, and as they did the genetic
base of agriculture was narrowed.
The disappearance of landraces is
not so critical in a place like Canada,
where the local crops were little
changed from their European ances-
tors, but it is more serious when it
takes place in Vavilov centres of the
world. For it is the genetic diversity
found in the landraces that allows
plant breeders to create new elite
varieties.
A plant breeder seeking to improve
a crop in some way — by adding
disease resistance or drought tolerance
— must go to a variety of the plant (or
a near relative) that exhibits the trait
and breed it with the elite stock. By
selecting offspring that exhibit both
the traits of the elite stock and the new
stock, then selectively breeding them,