Principles of Plant Genetics and Breeding

(in alloploids) or homologous (in autoploids) chromosomes
may make up for the missing functions.
Monosomics (2n − 1) may be used just like trisomics
to assign genes to chromosomes in a polyploid species.
This requires the development of monosomics for all the
existing chromosome pairs in the species, as was done by
E. R. Sears for the Chinese spring cultivar of wheat.
Nullisomics (2n − 2) may also be used in this fashion,
but with less success because of severe reduction in vigor
and fertility.
Chromosome substitution
Whereas alien chromosome addition entails adding an
alien chromosome to the genome of an existing genotype,
a chromosome substitution entails replacing or
substituting a chromosome of the recipient species with
an alien chromosome. Intervarietal (between varieties
of the same species) and interspecific chromosome
substitutions are more important in plant breeding than
the addition of chromosomes. One of the well-known
substitutions involves chromosome 1B of wheat and
chromosome 1R of rye. The resultant wheat cultivar
provided resistance to disease (leaf rust, stripe rust,
powdery mildew). To use this technique, there have to
be monosomic lines for the species (lines are available
for wheat, cotton, tobacco, and oats).
Bingham, E.T. 1980. Maximizing heterozygosity in autotetraploids.
In: Polyploidy: Biological relevance (Lewis,
W.H., ed.). Plenum Press, New York.
Borojevic, S. 1990. Principles and methods of plant breeding.
Elsevier, New York.
Chase, S.S. 1964. Analytic breeding of amphipolyploid plant
varieties. Crop Sci. 4:334–337.
Dewey, D.R. 1980. Some applications and misapplication
of induced polyploidy to plant breeding. In: Polyploidy:
Biological relevance (Lewis, W.H., ed.). Plenum Press, New
York.
Harlan, J.R., and J.M.J. de Wet. 1975. On a wing and a
prayer: The origin of polyploids. Bot. Rev. 41:361–390.
Haynes, K.G. 1992. Some aspects of inbreeding in derived
tetraploids of potatoes. J. Hered. 83:67–70.
Hermsen, J.G.Th. 1984. Nature, evolution, and breeding of
polyploids. Iowa State J. Res. 58:411–420.
POLYPLOIDY IN PLANT BREEDING 229
References and suggested reading
The backcross breeding procedure may be used to
substitute one chromosome for another in monosomics
or nullisomics. Such chromosome substitution may be
done within the species or involve other species (i.e.,
alien substitution). Researchers such as Sears have used
the technique to assign numerous genes to chromosomes.
However, the technique is challenging and
requires a great amount of cytological analysis.
Supernumerary chromosomes
Also called accessory or B-chromosomes, supernumerary
chromosomes are natural additions of varying
numbers of small chromosomes to the normal genome.
They have been found in all major taxonomic groups of
organisms. These chromosomes are often predominantly
heterochromatic and unstable in behavior. Although
largely considered as genetically inert, studies in some
species have indicated that the B-chromosomes increase
the recombination frequency of A-chromosomes (the
normal set of chromosomes) in species in which they
occur. It is possible to use certain breeding techniques
to increase their number. In some species such rye,
fertility is reduced by the presence of one or two
supernumerary chromosomes. However, corn plants
can accumulate at least 10 such chromosomes before an
adverse effect on fertility is noticeable.
Hill, R.R. 1971. Selection in autotetraploids. Theor. Appl.
Genet. 41:181–186.
Poehlman, J.M., and D.A. Sleper. 1995. Breeding field crops,
5th edn. Iowa State University Press, Ames, IA.
Sears, E.R. 1954. The aneuploids of common wheat. Missouri
Agric. Exp. Stn. Res. Bull. 572:1–58.
Singh, A.K., J.P. Moss, and J. Smartt. 1990. Ploidy manipulations
for interspecific gene transfer. Adv. Agron.
43:199–240.
Sterett, S.B., M.R. Henninger, G.C. Yencho, W. Lu, B.T.
Vinyard, and K.G. Haynes. 2003. Stability of internal heat
necrosis and specific gravity in tetraploid × diploid potatoes.
Crop Sci. 43:790–796.
Thomas, H. 1993. Chromosome manipulation and polyploidy.
In: Plant breeding: Principles and prospect (M.D.
Hayward, N.O. Bosemark, and I. Ramagosa, eds). Chapman
& Hall, London.