II.3. BRASSICA CROPS (BRASSICA SPP.) – 173
throughout Europe, parts of Africa, Asia and the Indian sub-continent before recorded
history. Excavations in China reported the presence of B. rapa seed at a
6 000-7 000-year-old archaeological site (Liu, 1985). Indian Sanskrit literature mentions
the plant about 1599 B.C. (Prakash, 1961), and Renfrew (1973) indicated that B. rapa
seed was consumed in Scandinavia as early as 350 B.C. B. rapa is grown as an oilseed
crop in northern Europe, north-west China, the foothills of the Himalayas and northern
India, while the vegetable forms were selected and modified in Asia, primarily in China.
The oilseed form was introduced to Canada by a Polish immigrant about 1936 (Boulter,
1983) and Australia began its first investigations on the B. rapa crop in the early 1960s
(Salisbury, 2002) but it has now been superseded by B. napus varieties. B. rapa also has a
weedy form that differs from the cultivated plant in exhibiting primary dormancy and has
a worldwide distribution (Figure 3.24).Figure 3.24. World distribution of B. rapa as a reported weed
Source: Modified from Holm et al. (1997).
B. oleracea
The centre of origin for the B. oleracea species is along the European Atlantic coast
while the wild related forms still grow on the islands and along the northern coast of
the Mediterranean. The various forms of this species were developed in Europe and
did not reach Asia until about the 16th century (Liu, 1985). The many cultivated forms of
this species have been introduced and grown worldwide, with the exception of some
tropical areas.B. napus
B. napus is of relatively recent origin (<10 000 years; see the section on genetics
at the end of this chpter and Figure 3.39) resulting from the interspecific cross between
plants of B. oleracea and B. rapa. The cross must have occurred where the two species
were growing in close proximity along the European Atlantic or Mediterranean coasts.
Dispersal of the species is thought to have occurred throughout Europe in the
16th century with the introduction to the Americas in the 17th and 18th centuries and
the Far East in the 19th century (Liu, 1985).