The artificial induction of new mutations has been employed when natural variation for a
trait is not available. However, it has the following disadvantages, and for these reasons, it is
considered by most breeders to be a technique of last resort:
- Most importantly, mutations are almost always deleterious, and it is highly unlikely
to find a beneficial mutation in a specific gene that affects a specific trait. Therefore,
any mutation breeding strategy must be capable of examining large numbers of
mutated progeny. - Mutations are often not noticeable in a first generation because they are in a hetero-
zygous state. Therefore, breeders must usually look at the offspring of a mutated
population. - Mutations are usually induced simultaneously in many different genes. Therefore,
even if a line is found with a desirable mutation, the same line probably caries
many other undesirable mutations that must be bred out. - Finally, there is the question of crop safety. It is possible that a new mutation may
have unpredictable effects on nontarget traits. This possibility can never be comple-
tely ignored, and for this reason, artificially induced mutations are considered by
some regulatory systems (including Canada’s) to be equivalent to artificial genetic
transformation events.
3.5.4 Apomixis
Apomixisis a genetic phenomenon whereby seed is produced without pollination. There are
several types of apomixis, but most types result in the production of seed that is identical in
genotype to that of the parent plant. Dandelion is a notorious weed that exhibits apomixis;
thus all of the seed from a single plant is likely to be identical. Very few cultivated crops
exhibit apomixis; these include Kentucky bluegrass (the other part of your lawn), and some
lesser-known tropical grasses. However, many research initiatives have attempted, or are
attempting, to introduce apomixis into other crops such as maize in order to take advantage
of the perpetual hybrid vigor that could be obtained if this were successful. One might
speculate that the amount of commercial interest in this endeavor is low, since this
would theoretically allow agricultural producers to save their own seed in a crop that
might otherwise require the continual purchase of hybrid seed.
3.6 Conclusions
Plant breeders—who are part scientists, part artisans, part entrepreneurs, part extension
workers, and part economists—are a special breed in themselves. Breeders have adopted
(and often instigated) many of the genetic discoveries made in the previous century, and
have developed highly scientific approaches to plant variety development. Yet these
approaches still leave ample room for personal philosophy, artistic license, and all of the
practical challenges of balancing objectives with reality. Over the next century, breeding
will incorporate new discoveries and new technologies, but it will almost certainly continue
to rely on the principles of sexual recombination and selection. Breeders, whether they are
part of industry, government organizations, or universities, will continue to be an essential
part of every bioeconomy, and the designation “plant breeder” will continue to describe an
interesting, challenging, and rewarding career.
3.6. CONCLUSIONS 77