Principles of Plant Genetics and Breeding

322 CHAPTER 17
Repeat cycle
Repeat cycle
Evaluate in field trial;
identify superior lines
Plant remnant seed
for crossing
Composite seed for
next cycle
Figure 17.6 Generalized steps in breeding by half-sib selection with a testcross.
Introduction
Source
population A
Source
population A 1
Bryan Kindiger
Source
population B
× × × ×
Source
population B 1
Select about 5 plants
from source population; self and
use to pollinate (about 200 plants)
of opposite source population
Industry highlights
Developing a new cool-season perennial grass forage:
interspecific hybrids of Poa arachnifera × Poa secunda
USDA-ARS Grazinglands Research Laboratory, El Reno, OK 73036, USA
An increasing awareness of the importance of sustainable grazing lands and the maintenance and enhancement of grasslands has
led to a greater interest in the genetic improvement of native species. The Poa genus contains examples of productive cool-season
perennial species that provide both turf and forage types. The genus is a variable one of about 300 species worldwide, of which
several are indigenous to the United States (Huff 1992). The wide variation within the genus, along with its predominantly
apomictic reproductive behavior, has made Poa a difficult genus with which to work. P. arachnifera Torr. (Texas bluegrass) is a
vigorous, rhizomatous, sod-forming perennial, native to the southern plains of the USA (Figure 1a) (Silveus 1933). The species is
dioecious, with male and female plants. To date, all of our native collections of P. arachnifera are completely sexual in their form
of reproduction. However, due to the excessive amount of cobwebby hairs located at the base of the lemma, seed harvest and
sowing of this species is difficult. P. secunda J. Presl. (big bluegrass) is also a native bluegrass (Figure 1b). It is an important component
of the sagebrush grassland vegetation of the western United States (Silveus 1933). It is distributed from southeastern Alaska
through the west and the Great Plains region of the USA. It is a long-lived perennial with a fibrous, bunch-type root system, which
can occasionally develop short rhizomes. P. secunda is also a facultative apomictic species exhibiting aposporic embryo sac
development (Kellogg 1987). The apomictic character of P. secunda is a second favorable characteristic that can be contributed
to hybrids and would allow the long-term maintenance of any hybrid vigor resulting from the hybridization of these two species.
Presumably, an extensive amount of genetic diversity exists in both P. arachnifera and P. secunda (Larson et al. 2001). By
utilizing the dioecious P. arachnifera as the female parent in interspecific hybridizations, large numbers of interspecific hybrids
can be rapidly generated. Such hybridization might be useful in developing diverse, native germplasm that could be widely
adapted and biologically appropriate to the central and southern plains of the USA.