194 – II.3. BRASSICA CROPS (BRASSICA SPP.)
Figure 3.33. Distribution of wild “species” of B. oleracea in 1990
Note: Introductions of B. oleracea outside its spontaneous area are not mapped.
Source: Modified from Snogerup, Gustafsson and Von Bothmer (1990).
B. napus
B. napus with its oilseed, forage and root forms is a relatively recent species.
The Greeks and Romans knew of the Swede or rutabaga root crop, but reference to these
forms does not appear in the ancient literature. Although Prakash and Hinata (1980) state
that no wild B. napus populations have been found, Linné reported wild forms growing
on the beaches of Gothland (Sweden), the Netherlands and Britain (cited by De Candole,
1885). Since the species is the result of an interspecific cross between a plant or plants of
B. rapa and the B. oleracea complex, it could only have arisen in the Mediterranean or
the European west coastal regions, where the two species were growing in close
proximity (Figure 3.33). Olsson (1960) suggested that B. napus could have arisen several
times by spontaneous hybridisation between different forms of B. rapa and B. oleracea.
Evidence from chloroplast and mitochondrial DNA suggests that B. montana might be
closely related to the maternal prototype that gave rise to B. napus (Song and Osborn,
1992). That B. oleracea was the maternal parent is supported by both Erickson, Straus
and Beversdorf (1983) and Ohkawa (1986). However, Flannery et al. (2006), using SSR
(simple sequence repeat) Brassica plastid markers, noted that B. rapa always grouped
with B. napus and concluded that B. rapa is the more likely plastid genome donor.
Further, Allender and King (2010), using chloroplast and nuclear markers, concluded that
it is highly unlikely that B. oleracea or any of the C genome species are closely related to
the maternal progenitor of most B. napus accessions. They suggest that a B. rapa strain
from northern Italy called “spring broccoli raab” may be the closest extant relative of the
B. napus maternal ancestor. However, the data also suggest that the interspecific cross
may have occurred more than once, with B. napus having multiple origins. Thus, the
