Principles of Plant Genetics and Breeding

esistance concerns (or “collateral resistance”) center
around four main aspects: (i) creating weeds out of cultivated
cultivars; (ii) creating “super weeds” from existing
weeds; (iii) creating resistant pests; and (iv) creating
antibiotic resistance in harmful microbes.
The problems vary in the probability of occurring.
The fact is that pests always manage to eventually adapt
to any pest management strategy that is implemented
repeatedly over a long period. This is especially true
when the organism has a short life cycle (e.g., bacteria
and many insects). The fear of creating a weed out of
cultivated crops engineered to be herbicide tolerant
stems from the fact that most modern herbicides have a
broad-spectrum action (i.e., kill many plant species).
Bioengineered herbicide-resistant crops are consequently
resistant to broad-spectrum herbicides. If, for
example Roundup Ready® soybean follows Roundup
Ready® corn, volunteer corn plants will resist
Roundup® and be a weed problem. Whereas crop rotations
are desirable, it should not involve crops engineered
with identical herbicide resistance. Further, using
the same herbicide repeatedly for a long time is not a
recommended agronomic practice, anyhow. Should a
farmer decide not to heed this advice, there are herbicides
besides glyphosate that can control Roundup
Ready® corn or soybean “weeds”.
On the issue of biotechnology contributing to the
development of “super weeds”, the potential exists
for gene escape from cultivated species engineered for
herbicide tolerance to interbreed with wild relatives,
thereby creating more competitive and difficult to control
weeds (so-called super weeds). While the movement
of transgenes into wild relatives of transgenic
crops is possible, this would occur only if the cultivated
crop species are grown where their weedy relatives with
which they can interbreed also occur. This is not the case
for the major crops that are transgenic for herbicide
resistance in the USA (e.g., corn, soybean, potato).
However, it is the case for squash and canola. It should
be pointed out that the development of resistance to
herbicides by weeds and other plants does occur, following
prolonged exposure to certain herbicides. Further,
irrespective of the herbicide or weed management tactic
used, resistance to the chemical over the long haul is
inevitable. This is why new herbicides will continue to
be needed. There is no evidence to suggest that development
of resistance is more problematic with the use of
transgenic crops than direct use of herbicides. The issue
of insects developing resistance to transgenic crops is
similar to the situation in weeds. Pests routinely overcome
management tactics used against them.
ISSUES IN THE APPLICATION OF BIOTECHNOLOGY IN PLANT BREEDING 277
To reduce the rate of insect-resistance development
to PIPs, producers of transgenic crops require customers
to grow a refuge of non-biotech and untreated
crops around the Bt crops. The idea is that the refuge
maintains an insect population susceptible to Bt that can
interbreed with any pests on the biotech product that
may develop resistance, and prevent the resistance from
becoming established in the population.
Certain biotechnology techniques utilize antibioticresistance
markers in developing transgenic crops.
Consequently, the products contain these genes that
can possibly be transferred to microbes in the environment.
The fact is that the antibiotic-resistance markers
used in crop development do not provide resistance to
most of the antibiotics used in the clinical setting.
Biotechnology products are unnatural and unsafe
Nature, and therefore anything natural, is perceived by
some as superior to anything artificial. Modern foods
that have been processed and modified in all and sundry
ways are making us sick, they perceive; hence, the
booming organic food and health food markets. Herbal
medicine is being actively promoted in Western societies.
The public is concerned about biotechnology
inadvertently introducing undesirable and unnatural
chemicals into the food chain. The fact is that the
public has embraced artificial components in food and
medicine for a long period of time. Western therapy is
almost exclusively dependent upon synthetic pharmaceuticals.
Food additives and coloring are used routinely
in both home and industrial food preparations. Instead
of adding these materials to food during preparation,
biotechnology seeks to make plants and animals produce
nutrition-augmenting materials via natural processes
to be included in the plant and animal tissues. For
example, instead of postharvest vitamin-enriching of
the product (e.g., rice) for value added, the plant is
engineered with the capacity to produce pro-vitamin A
(“Golden Rice”).
Some concerns of plant breeders
Apart from these social concerns, some of the key concerns
of interest to plant breeders include the following:
1 Genetic engineering technology produces transgenic
plants that are often useful as breeding materials. The
transgenic trait must be transferred into adapted cultivars
(via backcrossing) to develop useful cultivars.
Breeding by genetic engineering, hence, can be a
lengthy process and expensive.