ABSTRACT
L., syn.
campestris
; genome AA, 2n = 20) and cabbage (
Brassica oleracea
L.; genome CC, 2n = 18), resulting in a genome comprising the full chromosome complements of its two progenitors. Because no wild
B. napus
forms are known, it is assumed that the species arose relatively recently, in the Mediterranean region, where both of its two parental species concurred. The closely related amphidiploid
Brassica
oilseeds
B. juncea
(L.) Czern (Indian or brown mustard; genome AABB, 2n = 36) and
Brassica carinata
L. (Abyssinian or Ethiopian mustard; genome BBCC, 2n = 34) arose in the same manner after crosses of black mustard (
Brassica nigra
, (L.) Koch; genome BB, 2n = 16) with
B. rapa
and
B. oleracea
, respectively. Figure 7.1 (See color insert following page 144) shows the
Brassica
triangle of U (1935), which describes the genomic relationships between the amphidiploid
Brassica
oilseed species and their diploid progenitors. Today, oilseed rape (
B. napus
) is the most heavily produced oilseed crop in Europe, and only soybean has a greater importance worldwide. Production of spring canola is dominated by North America (particularly Canada) and the northern provinces of China, whereas western Europe and central and southern China are the major producers of winter oilseed rape. On the other hand, the
Brassica
oilseeds exhibit an extremely broad adaptation to different agroclimatic conditions, with the more drought-tolerant
B. juncea
predominant on the Indian subcontinent and — along with
B. napus
— increasing in popularity in Australia. For
B. juncea
, various putative centers of origin have been identified, and the variation in morphotypes indicates that different subspecies of
B. rapa
were involved as independent genome donors in different regions (Prakash and Hinata, 1980). Indian mustard is widely grown throughout Asia. In Ethiopia,
B. carinata
is still the major oilseed crop, and due to its drought tolerance and resistance to pests and pathogens, this species is also growing in interest as a potential alternative oilseed crop within crop rotations in the dry areas of southern Europe. Cold-tolerant varieties of the diploid species
B. rapa
are grown in western Canada, where the early maturity can present an advantage over
B. napus
and other
Brassica
oilseeds. On the Indian subcontinent, the
B. rapa
ecotypes brown sarson, yellow sarson, and toria have regional significance.
