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[SANET-MG] hybrid seeds
http://www.i-sis.org.uk/hybridSeed.phpISIS Press Release 02/09/05
Hybrid seed was the first step whereby agribusiness corporations wrested
control of seed away from farmers Prof. Joe Cummins and Dr. Mae-Wan Ho
A fully referenced version of this article is posted on ISIS members’
website. Details here
A brief history
Hybrid seed began with maize in the 1920s, and became extended to
vegetables and flowers; and more recently, rice and some forage crops.
Hybrid seeds are produced from naturally out-breeding crops, from which
inbred lines are produced by repeated self-pollination. The established
inbred lines are crossed to produce first generations (F1) hybrid seeds.
The hybrid seeds are prized because they produce uniform plants
benefiting from the effect called heterosis (hybrid vigor). Heterosis
can result in a large increase in yield over the inbred lines or
comparable lines that are out-crossing. The precise basis of heterosis
is still unclear, but epistasis and over-dominance are thought to be
involved. Epistasis is the interaction between different genes, and
over-dominance is a condition where the heterozygotes (genes represented
by two different versions) are superior to either homozygotes (gene
represented by the same versions). The F1 hybrid seed is heterozygous in
Hybrid seed is planted to produce a crop that is harvested for use.
Saving seed from the crop and planting it is undesirable because the two
different versions of the genes in the F1 hybrid segregate out in the
offspring, producing an extremely variable progeny. In other words, the
superior qualities of the F1 hybrid will have all disappeared. The
hybrid is obtained by crossing the inbred lines, which therefore, have
to be separately maintained. Thus, only the seed companies produce
hybrid seeds, and farmers must buy those seeds from the company every year.
Hybrid maize arose through the advocacy of a few influential Americans.
Foremost among the advocates was Henry A. Wallace, who became
vice-president of the United States.
Wallace graduated from University with an agriculture degree, and
studied statistics thereafter on his own. He later taught the subject at
Iowa State University and used his knowledge to develop the first
commercial hybrid maize. In 1926, he founded the Hi-Bred Corn company
(now Pioneer Hi-Bred Seed Company, a subsidiary of Dupont Chemical
Company), and later entered politics. He was made Secretary of
Agriculture before being elected vice-president of the United States.
Wallace was noted for his concern for the common man and envisioned
hybrid corn as a means of providing bountiful food at low prices for the
masses. The detailed history of hybrid corn and Wallace makes
fascinating reading [1-3].
The first corn hybrids were made by detasseling the plants of the
maternal inbred-line by removing the male flowers so that the female
flowers on the plants can only be fertilized by pollen produced from
plants of another, male line. The detasseling operation used to be
performed mainly by young girls employed during the summer months. Later
on, male-sterile lines were developed that did not produce fertile male
flowers or pollen. The male-sterile maternal lines were fertilized with
paternal lines that allowed the hybrid seed to produce both male and
female flowers. The male-sterile lines are most frequently altered in
the mitochondrial genome, leading to the inhibition of male flower
development . A number of such lines are now available.
The early development of male-sterile lines led to disaster, however.
The primary line used in the 1960s contained the T (Texas) cytoplasm
male-sterility gene; and by 1970, over 85% of the commercial maize
planted contained that gene. The gene also caused a pleiotropic
(multiple effects due to a single gene) susceptibility to a fungus
disease. During a damp 1970 summer, the disease spread widely
particularly in the summer corn belt. The impact on maize production was
disastrous, leading to a return to hand-detasseling for a number of
years until alternate male-sterility lines could be developed . The
lesson that should have been learned was that the absence of diversity
is bound to lead to disastrous epidemics; but that lesson tends to get
ignored in favour of risky but profitable genetic manipulations.
Rice hybrids have been produced using cytoplasmic male-sterility.
Over-dominance and epistatic genes were implicated as the basis for
heterosis (and inbreeding depression, a phenomenon in which inbred lines
suffer decreased yield) [6, 7]. Alfalfa interspecies hybrids showed
heterosis, interspecies hybrids are a little different from those
originating from inbred lines, but in general they act similarly to
inbred lines .
A large number of vegetable crops have been hybridized. Hybrid cucumbers
have been produced by hand pollination, removal of male flowers, or
gynoecy (property of producing only female flowers). There does not seem
to be an available male sterility gene (9). Hot and sweet peppers have
been hybridized. Both nuclear and cytoplasmic sterility are used in some
cases. Most hybrid-pepper seed production is carried out in China, India
or Thailand . About two-thirds of commercial onions are hybrids.
These are produced using male sterility lines . Hybrid cabbage shows
strong heterosis, and the use of such hybrids is expanding. The seed is
produced using male sterile lines .
Most of the male sterile lines used commercially contain mitochondrial
genes, but such genes are not readily available in a number of crops.
Genetic engineers have developed a system of male-sterility based on
transformation of the chloroplast with a gene for beta-ketothiolase that
interferes with fatty acid synthesis, leading to disrupted anther tissue
and a failure to produce pollen. The beta-ketothiolase gene is
controlled by a light sensitive promoter, so that male-fertility can be
restored in hybrids using several days of continual illumination [13,
14]. The system was developed in tobacco but may be extended to food
crops, barring unforeseen complications.
Genetically modified male-sterility
A number of genetically modified (GM) male-sterile crops have been
developed and tested in the field. In Canada, a male-sterile transgene
was introduced into the nuclear gnome of canola, and that construction
was approved for, and has been in commercial production. The transgenic
construct included a barnase ribonuclease gene controlled by a tapetum
promoter. Barnase kills pollen cells thus rendering the plant
male-sterile. In the hybrid male fertility is restored using the barstar
inhibitor of barnase , although barnase is well known to be toxic to
animal cells. Development continued, and the technology came to be used
to protect GM traits patented by agribusiness corporations such as
herbicide tolerance under the general rubric of genetic use restriction
technology (GURT). Such crops were extensively field tested in Europe;
and we have warned that the F1 hybrid grown in the field will actually
spread the barnase transgene as well as the herbicide tolerance gene in
pollen with potentially harmful ecological impacts (“Chronicle of an
ecological disaster foretold”, SiS 18) . Furthermore, the toxin may
well be carried over into the canola press cake used both for both food
The development of hybrid seed had left seed production to seed
companies for the practical reason that it is the most economical way to
maintain appropriate inbred lines, and seed production can be isolated
from the food production areas of open pollinating crops. But it had
also prevented farmers from saving and replanting seeds, making it
necessary to purchase seeds every season.
Biotechnology has gone a step further and demanded that seed production
be restricted to companies even when there is no rational basis for the
restriction, other than corporate greed. Goeshl and Swanson addressed
the question of GURT based on the hybrid-crop experience. They argued
that developed countries could benefit from the additional production
supposedly to be gained by the technology, while developing countries
will suffer from their inability to afford the high extra cost. They
predict net deterioration in the developing countries due to the
widening gap in productivity . These predictions must be taken with
a very large grain of salt. There is at present no evidence that genetic
use restriction technologies, or indeed, any genetic modification
technology have led to increase in crop yield. Furthermore, both hybrids
and GM crops lack the diversity required for sustainability in the
complex ecosystems of the developing world. What is needed is seed
production that takes into account the unique requirements of developing
countries, where the farmers’ rights to save, replant and exchange seeds
are integral to food sovereignty and food security (“SOS: Save our
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