Genetic improvement of underutilized cole crops (Brassica oleracea)

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.

References

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