The Application of Ooubled Haploid Plants to Population ... - MSpace

Brassita rapa represents approximately haif of canola produdion in Canada
(Askew, 1995). Traditional breeding rnethods with mis sporophytkatly
self-incompatible (SI) speàes have invdved mass seldon, hybridization or the
development of synthetics, al1 of which rely on outcrossing. Doubled haploid (OH) line
development is a breeding tool that has been shown to speed up the breeding proœss
by achieving homozygosity in a single generation and avoiding repeated generations of
inbreeding traditionally required to fix desirable traits (Chen and Beversdorf, 1999).
The production of DH plants in B. rapa results in inbreeding depression. In
order to make use of DH plants in population improvement, agronomic performance
rnust be restored. lnbreeding through DH production provides the opporhinity to fix
desirable alleles in homozygous condition Hile subsequent production of crosspollinated
composites can be used to restore vigour. The production of a composite
population involves the intercrossing and recombining of two or more open-pollinating
inbreds, DH lines or cultivars and is maintained sirnply by further random
interpollination. lntercrossing promotes the maintenance of heterozygosity and
heterogeneity in these populations which have been show to improve yield and yield
stability in B. napus hybrids (Léon, 1991 ).
Optimum population size is an important consideration in composite production.
In B. rapa populations it is aitical to have sufficient variation at the multi-allelic
S-locus, which controls SI. to ensure an adequate number of compatible mates. The