Canola, Rapeseed, and Mustard: For Biofuels and Bioproducts - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 144

and selection of pure breeding doubled haploid lines, and the development of
synthetics, varietal associations, and finally hybrids [ 1 ].
For B. juncea canola/mustard oilseed cultivars, breeding for improved seed yield
has involved successively selection within open-pollinated populations and crosses
of open-pollinated populations and pedigree selection of derived families and the
development and selection of pure breeding doubled haploid lines and more
recently hybrids [ 43 , 46 , 67 ].
For B. carinata mustard cultivars, breeding for improved seed yield has involved
successively selection within open-pollinated population landraces and crosses of
open-pollinated populations and pedigree selection of derived families [ 88 ].
A breeding strategy focusing on hybrids has developed in four Brassica oilseed
species because of reports of significant heterosis for seed yield. This strategy has
been coupled with a pollination control system development strategy to facilitate
the production of large quantities of hybrid seed for commercial use.
Reports of heterosis for seed yield in B. rapa [ 89 - 92 ] created interest in the
development of hybrid B. rapa cultivars using either self-incompatibility [ 46 ]or
cytoplasmic male sterility [ 16 ] pollination control systems.
Reports of heterosis for seed yield in B. napus [ 93 - 97 ] created interest in the
development of hybrid B. napus cultivars using genetic male sterility, self -incom-
patibility, or cytoplasmic male sterility [ 10 ]. Pollination control system develop-
ment in B. napus including cytoplasmic male sterility (CMS) systems [ 98 ], genetic
male sterility (GMS) systems [ 99 ], and self-incompatibility (SI) systems [ 100 ] has
been conducted for several decades. The nap CMS [ 101 ], pol CMS [ 102 ], mur CMS
[ 103 ], ogu CMS [ 104 ], and ogu INRA CMS [ 105 ] systems have been developed for
use in hybrid canola/HEAR seed production. Initially, absence of a restorer gene for
the ogu INRA CMS system resulted in the development of non-restored hybrid
canola cultivars (known as varietal associations) in Europe [ 2 ]. Varietal associa-
tions had widely varying seed yields correlated to the extent of insect cross-
pollination occurring in the field [ 2 ]. The development of restorer lines for the
ogu INRA CMS system produced a fully functional CMS system [ 106 -
108 ]. Genetic male sterility (GMS) systems have also been developed and evalu-
ated for use in hybrid canola/HEAR cultivar development [ 99 ]. The male sterile
Lembke (MSL) GMS pollination control system is widely used to produce hybrid
canola/HEAR cultivars globally. The development of a genetic male sterility
system based on recombinant DNA technology created a successful pollination
control system in B. napus based on barstar and barnase genes, both linked to broad-
spectrum novel herbicide tolerance [ 81 ]. This nuclear male sterility (NMS) polli-
nation control system is being used to produce very successful hybrid canola
cultivars globally. B. napus canola hybrids are being developed in Canada and
Europe using male sterile Lembke (MSL) GMS, Bayer CropScience nuclear male
sterility (NMS), and ogu INRA CMS pollination control systems [ 81 , 98 ]. A current
breeding objective in hybrid B. napus breeding is the expansion of the genetic
variability in the spring canola gene pool to maximize heterosis for yield in hybrids
[ 109 ]. In addition to the standard crosses using spring habit B. napus , spring habit-