Principles of Plant Genetics and Breeding

72 CHAPTER 4
Male-fertile
RfRf or
Rfrf or
rfrf
Normal
cytoplasm System A
Male-fertile
RfRf or
Rfrf
Sterile
cytoplasm System B
Male-sterile
rfrf
Sterile
cytoplasm System C
Nucleus
Figure 4.10 The three systems of cytoplasmic-genetic
male sterility. The three factors involved in CMS are the
normal cytoplasm, the male-sterile cytoplasm, and the
fertility restorer (Rf, rf ).
Cytoplasmic-genetic male sterility CMS may be
modified by the presence of fertility-restoring genes
in the nucleus. CMS is rendered ineffective when the
dominant allele for the fertility-restoring gene (Rf )
occurs, making the anthers able to produce normal
pollen (Figure 4.10). As previously stated, CMS is
transmitted only through the egg, but fertility can be
restored by Rf genes in the nucleus. Three kinds of
progeny are possible following a cross, depending on
Acquaah, G. 2004. Horticulture: Principles and practices, 3rd
edn. Prentice Hall, Upper Saddle River, NJ.
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.
References and suggested reading
the genotype of the pollen source. The resulting progenies
assume that the fertility gene will be responsible
for fertility restoration.
Exploiting male sterility in breeding
Male sterility is used primarily as a tool in plant breeding
to eliminate emasculation in hybridization. Hybrid
breeding of self-pollinated species is tedious and timeconsuming.
Plant breeders use male-sterile cultivars as
female parents in a cross without emasculation. Malesterile
lines can be developed by backcrossing.
Using genetic male sterility in plant breeding is problematic
because it is not possible to produce a pure
population of male-sterile plants using conventional
methods. It is difficult to eliminate the female population
before either harvesting or sorting harvested seed.
Consequently, this system of pollination control is not
widely used for commercial hybrid seed production.
However, CMS is used routinely in hybrid seed production
in corn, sorghum, sunflower, and sugar beet.
The application of male sterility in commercial plant
hybridization is discussed in Chapter 18.
Genotype conversion programs
To facilitate breeding of certain major crops, projects
have been undertaken by certain breeders to create
breeding stocks of male-sterile lines that plant breeders
can readily obtain. In barley, over 100 spring and winter
wheat cultivars have been converted to male-sterile lines
by US Department of Agriculture (USDA) researchers.
In the case of CMS, transferring chromosomes into foreign
cytoplasm is a method of creating CMS lines. This
approach has been used to create male sterility in wheat
and sorghum. In sorghum, kafir chromosomes were
transferred into milo cytoplasm by pollinating milo with
kafir, and backcrossing the product to kafir to recover all
the kafir chromosomes as previously indicated.
de Nettancourt, D. 1977. Incompatibility in angiosperm.
Springer-Verlag, Berlin.
Edwardson, J.R. 1970. Cytoplasmic male sterility. Bot. Rev.
36:341–420.
Foskett, D.E. 1994. Plant growth and development.
Academic Press, San Diego, CA.