Principles of Plant Genetics and Breeding

R. C. Buckner and his colleagues succeeded in crossing
the diploid Italian ryegrass (Lolium multiflorum, 2n =
2x = 14) with the hexaploid tall fescue (Festuca arundinacea,
2n = 6x = 42) via the bridge cross technique. The
intermediate cross was between L. multiflorium and
diploid meadow fescue (Fescue pratensis, 2n = 2x = 14).
The resulting embryo was rescued and the chromosome
number doubled to produce a fertile but genetically
unstable tetraploid hybrid (ryegrass–meadow fescue), to
be used as a genetic bridge. Using tall fescue as the
recipient, the genetic bridge was repeatedly backcrossed
to tall fescue. A 42-chromosome cultivar of tall fescue
with certain Italian ryegrass traits was eventually recovered
and stabilized.
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Part A
Please answer the following questions true or false:
SEXUAL HYBRIDIZATION AND WIDE CROSSES IN PLANT BREEDING 179
References and suggested reading
Outcomes assessment
1 A hybrid is a product of unidentical parents.
2 Emasculation is undertaken to make a flower female.
3 An integeneric cross occurs between two species.
4 Wheat is a product of a wide cross.
5 Bridge crosses are used to facilitate crosses between two parents of identical ploidy levels.
Part B
Please answer the following questions:
1 What is hybridization?
2 What are wide crosses?
Developing new species via wide crossing
A species is defined as a population of individuals capable
of interbreeding freely with one another but which,
because of geographic, reproductive, or other barriers,
do not in nature interbreed with members of other
species. One of the long-term “collaborative” breeding
efforts is the development of the triticale (× Triticosecale
Wittmack). The first successful cross, albeit sterile, is
traced back to 1876; the first fertile triticale was produced
in 1891. The development of this new species
occurred over a century, during which numerous scientists
tweaked the procedure to reach its current status
where the crop is commercially viable. Triticale is a wide
cross between Triticum (wheat) and Secale (rye), hence
triticale (a contraction of the two names). It is a predominantly
self-fertilizing crop, and the breeding of
triticale is discussed in Chapter 13.
Mallory-Smith. 2002. Jointed goatgrass (Aegilops cylindrica
Host) × wheat (Triticum aestivum L.) hybrids:
Hybridization dynamics in Oregon wheat fields. Crop Sci.
42:1863–1872.
Singh, A.K., J.P. Moss, and J. Smartt. 1990. Ploidy manipulations
for interspecific gene transfer. Adv. Agron. 43:199–240.
Stalker, H.T. 1980. Utilization of wild species for crop
improvement. Adv. Agron. 33:111–147.
Stoskopf, N.C. 1993. Plant breeding: Theory and practice.
Westview Press, Boulder, CO.
Zohary, D. 1973. Gene-pools for plant breeding. In:
Agricultural genetics (R. Moav, ed.). John Wiley & Sons,
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