Principles of Plant Genetics and Breeding

212 CHAPTER 12
undesirable side effects such as sterility. To do that,
the new mutant must be successively propagated for
several generations and sometimes even crossed with
other genotypes.
2 Large numbers of segregating populations are
needed. Another weakness is the need to produce and
sort out a large number of segregating populations in
order to have a good chance of finding a desirable
mutant. Most mutations are deleterious or undesirable.
Mutation breeding may be likened to finding a
needle in a haystack. To sort through all the garbage,
the plant breeder should have an easy method of
screening the enormous variation. Morphological
changes (e.g., shape, color) are easy to screen. However
subtle changes require more definitive tests to
evaluate and hence are more expensive to undertake.
3 Recessivity of mutants. Most mutations are recessive
and hence are observed only when the homozygous
genotype occurs. This condition is readily satisfied in
species that are naturally inbreeding. The situation
practically excludes species that are polyploid, propagated
clonally, or have a fertility-regulating mechanism
(e.g., self-incompatibility) from being amenable to
mutation breeding (except when dominant mutations
are targeted).
4 Limited pre-existing genome. The researcher cannot
change what does not exist. Consequently, mutations
can only be induced in existing genes.
5 Mutations are generally random events. A modern
biotechnology technique, site-directed mutagenesis,
has been used to induce targeted mutations. However,
conventional mutagenesis remains unpredictable and
can not be directed to specific genes.
Selected significant successes of
mutation breeding
Mutation breeding has been used to improve a number
of important crops (Table 12.3). The first commercial
Anon. 1991. Plant mutation breeding for crop improvement.
Proceeding of the FAO/IAEA Symposium, Vienna, 1990.
International Atomic Energy Agency, Vienna.
Broertjes, C., and A.M. Van Harten. 1988. Applied mutation
breeding for vegetatively propagated crops. Elsevier,
Amsterdam.
Micke, A. 1992. Fifty years induced mutations for improving
disease resistance of crop plants. Mutation Breed. Newsl.
39:2–4. IAEA, Vienna.
References and suggested reading
Table 12.3 Selected general areas of achievement in
mutation breeding.
Disease resistance: e.g., Verticilium wilt resistance in
peppermint, victorial blight resistance in barley, downy
mildew resistance in pearl millet
Modification of plant structure: e.g., bush habit in dry
bean, dwarf mutants in wheat and other cereals
Nutritional quality augmentation: e.g., opaque and floury
endosperm mutants in maize
Chemical composition alteration: e.g., low euricic acid
mutants of rape seed
Male sterility: for use in hybrid breeding in various crops
Horticultural variants: development of various floral
mutants
Breeding of asexually propagated species: numerous
species and traits
Development of genetic stock: various lines for breeding
and research
Development of earliness: achieved in many species
cultivar derived from mutagenesis was “Chlorina”, a
tobacco cultivar. It was developed with X-ray radiation
in 1930. Since then, several hundreds of commercial
cultivars or ornamentals, field crops, fruit crops, and
other plant kinds have been released for production.
These include barley cultivars “Pallas” and “Mari” that
were developed by Swedish scientists. These genotypes,
and other cultivars developed through hybridizations
involving the two mutants, significantly impacted barley
production in Denmark and Sweden. In the USA,
“Pemrad” and “Luther” cultivars of barley were
significant in the production of the crop in the 1970s.
Dwarf cultivars of cereals have been developed by
mutagenesis. Classic examples are “Norin 10” of the
Green Revolution fame, and “Calrose 76” rice that
strongly impacted California rice production.
Peloquin, S.J. 1982. Meiotic mutants in potato breeding.
Stadler Symp. 14:99–109.
Pozniak, C.J., and P.J. Huel. 2004. Genetic analysis of imidazoline
resistance in mutation-derived lines of common
wheat. Crop Sci. 44:23–30.
Rasmusson, D.C., and R.L. Phillips. 1997. Plant breeding
progress and genetic diversity from de novo variation and
elevated epistasis. Crop Sci. 37:303–310.