Principles of Plant Genetics and Breeding

Sexually
reproductive
Apomict
New cultivar
×
Figure 11.2 Steps in a method for breeding apomictic
species.
plants produce adequate amounts of viable pollen to be
usable as males in crossing. This leaves the identification
of a suitable female the first critical step in an apomictic
improvement program.
TISSUE CULTURE AND THE BREEDING OF CLONALLY PROPAGATED PLANTS 197
Apomictic Hybridization produces
new gene combinations
Obligate apomict Will produce three
apomicts: five sexual
plants; select superior
Sexually
reproductive plants
F 2
apomicts
F 2 produces reduced
vigor in apomicts
Chaudhury, A.M., L. Ming, C. Miller, S. Craig, E.S. Dennis,
and W.J. Peacock. 1997. Fertilization-independent seed
development in Arabidopsis thaliana. Proc. Natl. Acad. Sci.
USA 94:4223–4228.
Hanna, W.W., and E.C. Bashaw. 1987. Apomixis: Its identification
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Jain, M., K. Chengalrayan, M. Gallo-Meacher, and P. Misley.
2005. Embryogenic callus induction and regeneration in a
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References and suggested reading
Once suitable parents have been selected, crossing
can be conducted as for regular plants. A sexual female
plant may be crossed with an apomictic male to produce
F 1 hybrids, some of which will be obligate and true
breeding apomicts, while others will be asexual hybrids
that will segregate in the F 2 (Figure 11.2). Because
apomicts are generally heterozygous, selfing of sexual
clones will yield variability from which the breeder can
practice selection. The use of markers and precautions in
emasculation will help in distinguishing hybrids from
other heterozygous plants. It should be pointed out that
the breeder should aim to identify superior genotypes in
the F 1 where heterosis is at a maximum, rather than in
later sexual generations.
As previously indicated, facultative apomicts are more
challenging to improve, partly because the breeder cannot
control variation in their progenies (they produce
both sexual and apomictic plants). Furthermore, the
stability of the reproductive process is influenced
by environmental factors (especially photoperiod).
Photoperiod has been observed to significantly affect
the relative frequency of sexual versus apomictic embryo
sacs in ovules of certain species.
Mohammadi, S.A., B.M. Prasanna, and N.N. Singh. 2003.
Sequential path model for determining interrelationship
among grain yield and related characters in maize. Crop Sci.
43:1690–1697.
Murashige, T., and T. Skoog. 1962. A revised medium for
rapid growth and bioassays with tobacco tissue culture.
Physiol. Plantar. 15:473–497.
Scityavathi, V.V., P.P. Janhar, E.M. Elias, and M.B. Rao.
2004. Effects of growth regulators on in vitro plant regeneration
in durum wheat. Crop Sci. 44:1839–1846.
Stefaniak, B. 1994. Somatic embryogenesis and plant regeneration
of gladiolus. Plant Cell Rep. 13:386–389.
Tae-Seok, K.O., R.L. Nelson, and S.S. Korban. 2004.
Screening multiple soybean cultivars (MG 00 to MG VIII)
for embryogenesis following Agrobacterium-mediated transformation
of immature cotyledons. Crop Sci. 44:1825–
1831.
Trigiano, R.N., and D.J. Gray (eds). 1996. Plant tissue culture
concepts and laboratory exercises. CRC Press, New York.