Harmonisation of Regulatory Oversight in Biotechnology Safety Assessment of Transgenic Organisms in the Environment, Volume 5..

II.3. BRASSICA CROPS (BRASSICA SPP.) – 241

A line, and the R line with a nuclear gene that restores fertility. The R line should be

highly heterotic to the A line to produce a high yielding, fully fertile F 1 commercial crop

(Figure 3.45).

China developed the first B. napus commercial CMS system, known as the Polima

system (Fu et al., 1997). However, the Polima system is rapidly being replaced in western

breeding programmes with the ogu-INRA system, the Male Sterile Lembke (MSL)

system and others under development (Stiewe et al., 1995; Prakash et al., 1995; Downey

and Rimmer, 1993).

A transgenic pollen control-restorer system, developed by Plant Genetic Systems and

commercialised by Bayer CropScience, is in widespread use in Canada and the United

States. Details of how this system functions are outlined by Downey and Rimmer (1993).

Figure 3.45. Production system for cytoplasmic male sterile hybrid seed of oilseed rape

Note: The small circle represents the nucleus showing the fertility restorer genes r and R and the larger circle
the cell with cytoplasm containing fertile (F) or sterile (S) mitochondrial genes.

Source: Modified from Buzza (1995).

Improvement through “interspecific hybrids” and “cybrids”

Interspecific and intergenomic crosses are important options for the introduction of

desired traits that are not available, or cannot be found, within the primary gene pool of a

crop species. Normally such crosses are difficult to make. As noted previously, there are

many natural barriers, both pre- and post-fertilisation, that protect the integrity of a

species. Further, even if such crossing is successful, chromosome pairing and alien gene

introgression into the genome of the target species must occur.

However, in the Brassicaceae, a number of desirable nuclear genes from different

genera and species have been transferred to targeted crop species. A list of traits that have

been transferred to B. napus, B. juncea and/or B. oleracea from other Brassicaceae

species is presented in Table 3.16 (Prakash et al., 2009).

Insect

pollination

strip cropping

S F

S

x

S

F or S

x

B line

maintains A line

rr rr

rr RR

R line

restores fertility

Rr

A line

lacks pollen

A line

lacks pollen

Commercial F 1

hybrid

Insect

pollination

strip cropping