Singh BK and Singh B. 2016. Genetic improvement
of underutilized cole crops (Brassica oleracea). In: Advances in
Genetic Enhancement of Underutilized Vegetable Crops (Singh B, Singh PM, Ranjan
JK, Singh BK, Pragya and Tiwari SK Eds). Training Manual No. 68, ICAR-IIVR, Varanasi, UP, pp 69-78.
The use of the term underutilized to refer to categories of wild and
cultivated plants invariably gives rise to a discussion of what the word
actually means. Usually, it is commonly applied to the species whose potential
has not been fully realized, but they are part of a larger biodiversity
portfolio. These species are no longer competitive with the crops which
dominate the food supply and that are supported by seed supply systems,
production and post-harvest technologies and extension services. In order to
bring underutilized species back into cultivation, their affordability has to
be addressed and new opportunities such as new food, nutritional significance,
and developments taking place in genetic improvement, production knowhow and
post-harvest technologies have to be explored.
Cole crops (Brassica oleracea) are a group of highly
differentiated plants having
18 numbers of diploid and somatic chromosomes, and these are grown all over the
world from arctic to tropical climatic conditions. The word
‘cole’ seems to have been derived from the abbreviation of the word ‘caulis’
meaning stem/cabbage/stalk. Variation within and between subspecies of B. oleracea, and present day cultivated
cole crops (kale, broccoli, cauliflower, cabbage, kohlrabi and Brussels sprout)
have evolved after a long time of natural/artificial hybridization, mutation,
selection and domestication. All these forms are descended from a common kale like ancestor, the wild
cabbage (B. oleracea L. var.
sylvestris L.) which is still prevalent in the western and southern
Europe, and North Africa (Table 1). Taxonomically,
the cole crops belong to the order Brassicales (Cruciales), family Brassicaceae
(Cruciferae), tribe Brassiceae, subtribe Brassicinae, genus Brassica, section Brassica and species oleracea (Singh 2015). Among
cultivated six cole crops, the following three i.e. kale, kohlrabi and Brussels
sprout have the status of underutilized cole crops. The economic parts used in
the present day cole crops are stem, leaves, flower or modified forms which
have been named as curd, head, knob or leaf (Table 2).
Table 1: Evolution of cultivated B. oleracea crops (Prakash
et al. 2011, Singh 2015)
|
Probable
sequence of evolution
|
Scientific
name
(B. oleracea var.)
|
Common
name
|
Ancestor*
|
|
1
|
var.
sylvestris L.
|
Wild
cabbage
|
-
|
|
2
|
var. ramosa DC.
|
Thousand-head
kale,
branching
bush kale
|
1
|
|
3
|
var. gemmifera DC.
|
Brussels
sprouts
|
2
|
|
4
|
var. dalechampii
|
|
3
|
|
5
|
var. costata DC.
|
Portuguese
tree kale, tronchuda kale
|
1
|
|
6
|
var. medullosa Thell.
|
Marrow-stem
kale
|
1
|
|
7
|
Intermediate between 6 & 8
|
|
6
|
|
8
|
var. gongylodes L.
|
Kohlrabi
|
7
|
|
9
|
var. sabauda L.
|
Savoy
cabbage
|
5
|
|
10
|
var. capitata L.
|
White
cabbage
|
9
|
|
11
|
var. capitata L.
|
Red
cabbage
|
10
|
|
12
|
var. viridis L.,
var. sabellica L.,
var. palmifolia DC.
|
Kale
and collards
|
1
|
|
13
|
var. italica Plencks
|
Broccoli,
Calabrase
|
12
|
|
14
|
var.
botrytis L.
|
Cauliflower
(biennial)
|
13
|
|
15
|
var. botrytis L.
|
Cauliflower
(annual)
|
14
|
|
16
|
var. botrytis L.
|
Cauliflower
(Indian) or Tropical cauliflower
|
15
|
*Ancestors
are represented by numerical letters (1 to 15) of evolution along with
corresponding scientific name.
Table
2: Edible parts of cole crops
|
Cole crop
|
Edible part
|
|
Kohlrabi
|
Knob, swollen/enlarged stem and globular in shape, just above the soil line which has a short growing
season in cool weather because it should be harvested when young and tender.
|
|
Brussels sprouts
|
Sprouts (resemble as small cabbage) i.e. swollen axillary buds (2.5-5.0 cm in diameter) which arise along the
stem of the plant.
|
|
Kale and collards
|
Non-heading cole vegetables, grown mostly for tender leaves and shoots.
|
|
Sprouting broccoli
|
Head, composed of fully functional flower buds
|
|
Cauliflower
|
Curd, described as pre-floral fleshy apical meristem in which the lateral buds of shoot meristem are
elongated and much branched, and apices of these branches form the structure
of curd of
which >90% abort prior to flowering
|
|
Cabbage
|
Head, shortening of leaf petiole and inward cupping of leaf. After the rosette stage, new leaves develop with
shorter petioles and the leaves begin to cup inward to form head.
|
|
Savoy cabbage
|
Head with crinkled leaves
|
Nutritional
composition
Cole crops are rich in nutrients, including
several carotenoids (beta-carotene, lutein, zeaxanthin); vitamins C, E, and K;
folate; antioxidants and minerals (Farnham
et al. 2000, Podsedek 2007, Singh 2007). In
addition, these cruciferous vegetables contain a group of substances known as
glucosinolates which are responsible for the pungent aroma and bitter flavours.
Kale is most nutritious cole as well as leafy vegetable “King of the
Nutritional Powerhouses”. It is packed with vitamins, like K and C; loaded with
β-carotene and calcium; possesses high antioxidant activity; and contains a
very potent anti-cancer compound called sulforaphane (Table 3 and Table 4,
http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/). Kale
is an excellent source of dietary carotenoids and has the highest concentration
of lutein and b-carotene of any vegetable. Dietary intake of foods rich in
lutein and β-carotene is associated with reduced risk of lung cancer and
chronic eye diseases.
Table 3: Nutrient content in cole and leafy
vegetable
|
Nutrient
(per 100 g raw edible
portion)
|
Kale
|
Cabbage
|
Broccoli
|
Spinach
|
Amaranth
|
Bathua
|
|
Calories (kJ)
|
50.0
|
24.9
|
34.0
|
23.0
|
22.9
|
43.0
|
|
Carbohydrate (g)
|
10.0
|
5.8
|
6.6
|
3.7
|
3.9
|
7.3
|
|
Dietary Fiber (g)
|
1.9
|
2.5
|
2.6
|
2.3
|
0.0
|
4.0
|
|
Sugars (g)
|
0.0
|
3.1
|
1.6
|
0.3
|
0.0
|
|
|
Total Fat (g)
|
0.7
|
0.1
|
0.3
|
0.3
|
0.4
|
1.0
|
|
Omega-3 fatty acids (mg)
|
180.6
|
0.0
|
21.0
|
138.0
|
2.1
|
36.0
|
|
Omega-6 fatty acids (mg)
|
137.9
|
17.0
|
17.0
|
26.0
|
145.0
|
315.0
|
|
Protein (g)
|
3.3
|
1.2
|
2.9
|
3.0
|
2.5
|
4.2
|
|
Vitamin A (IU)
|
15376
|
98
|
623.1
|
9377
|
2918
|
11600
|
|
Beta carotene (mcg)
|
9227
|
42
|
0.0
|
5627
|
|
|
|
Lutein+Zeaxanthin (mcg)
|
39551
|
30
|
0.0
|
12197
|
|
|
|
Vitamin C (mg)
|
120.0
|
36.6
|
89.2
|
28.0
|
43.2
|
80.0
|
|
Vitamin E (mg)
|
-
|
0.1
|
0.8
|
2.0
|
||
|
Vitamin K (mcg)
|
816
|
76
|
101.6
|
483
|
1139
|
|
|
Thiamin
|
0.1
|
0.1
|
0.1
|
0.0
|
0.0
|
0.2
|
|
Riboflavin (mg)
|
0.1
|
0.0
|
0.1
|
0.3
|
0.0
|
0.4
|
|
Niacin (mg)
|
1.0
|
0.2
|
0.7
|
0.7
|
0.7
|
1.2
|
|
Vitamin B6 (mg)
|
0.3
|
0.1
|
0.2
|
0.3
|
0.4
|
0.3
|
|
Folate (mcg)
|
29.0
|
43.0
|
63.0
|
194.0
|
85.0
|
30.0
|
|
Choline (mg)
|
0.0
|
10.7
|
18.7
|
18.0
|
0.0
|
|
|
Ca (mg)
|
135.1
|
40.0
|
47.0
|
99.0
|
215.0
|
309.0
|
|
Fe (mg)
|
1.6
|
0.4
|
0.8
|
2.7
|
2.1
|
1.2
|
|
Mg (mg)
|
34.0
|
12.0
|
21.0
|
79.0
|
55.0
|
34.0
|
|
P (mg)
|
56.0
|
26.0
|
66.0
|
49.0
|
50.0
|
72.0
|
|
K (mg)
|
446.3
|
169.7
|
316.5
|
556.7
|
610.7
|
452.0
|
|
Na (mg)
|
43.0
|
18.0
|
33.0
|
79.0
|
20.0
|
43.0
|
|
Zn (mg)
|
0.4
|
0.2
|
0.4
|
0.7
|
1.1
|
0.4
|
|
Cu (mg)
|
0.3
|
0.0
|
0.0
|
0.0
|
0.0
|
0.3
|
|
Mn (mg)
|
0.7
|
0.1
|
0.2
|
1.0
|
0.7
|
0.8
|
|
Se (mcg)
|
0.9
|
0.3
|
2.5
|
1.0
|
1.1
|
0.9
|
|
Water (g)
|
84.5
|
92.1
|
89.3
|
91.3
|
91.8
|
84.3
|
Table 4: Antioxidant activity in cole crops (Cao et
al. 1996)
|
Cole crop
|
Antioxidant activity (µmol of Trolox/g)
|
|
Kale
|
17.7
|
|
Brussels sprouts
|
9.8
|
|
Broccoli
|
8.9
|
|
Cauliflower
|
3.8
|
|
Cabbage
|
3.0
|
Vernalization
For bolting and flowering, most of the cole crops are generally performed
on mature vegetative plants either in-situ or ex-situ at temperatures between
5-10 °C for 30-60 days i.e. vernalization other than tropical varieties/genotypes
(Table 5). Two main climatic factors should be taken in to
consideration while selecting the area for seed production of cole crops. The
most important one is the temperature during winter which is critical for
vernalization; and other one is the precipitation/rainfall during the season of
flowering, seed maturity and harvesting. Like
all Cole crops other than tropical cauliflower, kale
requires low temperature exposure (4.5-10 °C temperature for 60 days) viz.
vernalization to stimulate and induce bolting i.e. inflorescence stalk
differentiation (Verma and Sharma 2000). ICAR-Indian
Institute of Vegetable Research, Varanasi, Uttar Pradesh has developed a of
tropical kale ‘VRKALE-1’ which bolts and flowers
under North Indian plain conditions (11.8-23.5 °C temperature) and doesn’t
require vernalization.
Prospects
The underutilized cole crops namely kohlrabi, kale and Brussels sprouts
will remain a rather insignificant and underutilize vegetable for the tropical
regions of world; unless there are serious research efforts being made to promote and utilize genetic
resources; and to develop heat-tolerant and tropical cultivars. The possibility
of inter-specific hybridization by utilizing the genes from tropical
cultivars/genotypes of other cole vegetables will certainly widen gene-pool,
and pave the way forward to develop tropical varieties/hybrids of the
underutilized cole vegetables, and eventully their popularization and
cultivation.
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