chapter  7
36 Pages

Brassica Oilseeds

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.