Vegetable brassicas, also known as cole crops, which are derived from the Latin
word caulis (Wikipedia, the free encyclopedia) are important vegetables known to
mankind for over 4,000 years. Records show that the Ancient Greeks, Romans,
Indians and Chinese all valued and used them greatly. Mankind took both the
wild parents and their hybrid progeny, refined them by selection and further
combination, and produced over biblical time crops that are, together with the
cereals, the mainstay of world food supplies (Dixon, 2007). Currently, the estimated
production is about 58 million tons from about 3 million ha of agricultural land
cultivated with cabbages. China remained the leading producer of cabbage (740230
ha), followed by India (300500 ha) and Russian Federation (115600 ha) (FAOSTAT
Collectively, brassicas deliver leaf, flower and root vegetables that are eaten
fresh, cooked and processed; used as fodder and forage, contributing especially
overwintering supplies for meat and milk producing domesticated animals; sources
of protein and oil used in low fat edible products, for illumination and industrial
lubricants; condiments such as mustard, herbs and other flavorings; and soil
conditioners as green manure and composting crops.
The regular consumption of vegetables, specifically the dark green leafy
vegetables is highly recommended because of their potential in reducing the risks
of chronic diseases. These vegetables are important food crops because they provide
adequate amounts of dietary vitamins and minerals for humans (Miller-Cebert
et al., 2009). Among brassica crops broccoli is considered a very good source of
vitamins A and C; rich in potassium, calcium and phosphorus. Brussels sprout is a
very good source of vitamins A and C, rich also in potassium and folate. Cauliflower
is a good source of vitamin C, folate and potassium. It supplies small amounts of
several minerals and vitamins to the diet. Cabbage is an excellent source of vitamin
C. In addition to containing some B vitamins, cabbage supplies some potassium
and calcium to the diet (
cole_crops.pdf). The chemical composition of cole crops is depended on the growing

cycle. Total chlorophyll and phenolic contents, and particularly the total antioxidant
activity found at the individual stages were much higher in spring in comparison
with the autumn. The main factor which caused this variability seems to be the
isolation (Leja et al., 2002).
More generally brassicas are seen as functional foods with long-term roles in the
fight against cancer and coronary diseases. The Brassica vegetables are becoming
increasingly seen as contributing substantially to the long-term health of consumers.
In addition to providing high levels of fibre, vitamins and minerals, the brassicas
contain glucosinolates that are hydrolyzed into isothiocyanates by the action of
myrosinase enzymes. Increased consumption of glucosilonates from Brassica
vegetables is associated with reduced risk of cancer induction and development
(Kang et al., 2006). The content of glucosinolates, as well as the ratio among different
groups of glucosinolates (aliphatic, indole, and aromatic) differs with regard to
environmental influence (Bohinc and Trdan, 2012). Manipulating N and S fertility
may be one means of altering glucosinolates concentration and profiles in cabbage
and thereby potentially increasing health benefits of consuming this vegetable
(Rosen et al., 2005).
Recently, the tiny cruciferous weed Arabidopsis thaliana has become very
important for molecular biology, proving important educational and research tools.
Arabidopsis has a simple five-chromosome genome with minimal levels of
duplication, making it an ideal plant for research. The research from Arabidopsis
is being used to study the functioning of important genes involved in the horticulture
and agronomy of Brassica crop species, including the genes responsible for head
formation in cauliflower and broccoli (Lan and Paterson, 2000).

Botany and Phenology of Brassica Crops
The development of Brassica crops passes through several stages (Fig. 4.1) as
described by Feller et al. (1995). Germination (beginning of seed imbibitions, radicle
emerged from seed, hypocotyl with cotyledons breaking through seed coat,

emergence: cotyledons break through soil surface). Leaf development (cotyledons
completely unfolded; growing point or true leaf initial becomes visible, true leaf
unfolded). Development of harvestable vegetative plant parts (heads begin to form:
the two youngest leaves do not unfold, typical size, form and firmness of heads
reached). Inflorescence emergence (main shoot inside head begins to elongate, first
individual flowers of main inflorescence visible (still closed), first individual flowers
of secondary inflorescences visible (still closed), first flower petals visible; flowers
still closed). Flowering (first flowers open, flowering finishing: majority of petals
fallen or dry). Development of fruit (first fruits formed, fruits have reached typical
size). Ripening of fruit and seed (beginning of ripening: Fully ripe: seeds on the
whole plant of typical color and hard). Senescence (leaves and shoots beginning to
discolour, 50% of leaves yellow or dead, plants dead).

Flower and fruit development
The flower differentiates by the successive development of four sepals, six stamens,
two carpels and four petals (Dixon and Wallace, 1986). Flower opening starts in
the afternoon. Usually the flowers become fully expanding during the following
morning. Pollination of the flowers is by insects, particularly bees, collecting pollen
and nectar, which is secreted by four nectaries situated between bases of the short
stamens and the ovary (Fig. 4.2). The flowers are borne in racemes on the main
stem and its axillary branches. The inflorescences may attain lengths of 1–2 m.

After fertilization, the endosperm develops rapidly, while embryo growth does
not start for some days. The embryo is generally still small 2 weeks after pollination,
and fills most of the seed coat after 3–5 weeks. Nutrient reserves for germination
are stored in the cotyledons, which are folded together with the embryo radicle
lying between them (Dickson and Wallace, 1986). The fruits of cabbage crops are
glabrous siliquae (pods), 4–5 mm wide and 40–100 mm long, with two rows of seeds
lying along the edges of the replus. One silique contains 10–30 seeds. Three to 4
weeks after the opening of a flower, the silique reaches its full length and diameter
and getting mature.

Flower induction
In contrast to cauliflower and broccoli, flower induction in cabbage and Brussels
sprouts is not required for commercial crop production other than for seed
production. The induction of flowering in cabbage (Brassica oleracea) is brought
about by relatively low temperatures, in a process called vernalization. Anyway,
the temperatures are effective only if the plants are past what is called the juvenile
period. During the juvenile period, assimilates are used preferentially for leaf growth
rather than for apical meristem growth. Thus under conditions of limited resources,

leaf growth would be prolonged at the expense of meristem development. From a
practical standpoint, the existence of a juvenile period permits the plant to grow to
an adequate size before it can be induced to flower.
Optimum vernalizing temperatures of cabbage range from 4 to 10°C, although
there are cultivar differences in the temperatures. Plant age and size when inducing
temperatures are applied, play important roles in determining the rate and
effectiveness of the flower induction. Transplant age had a significant effect on the
total yield of broccoli heads (Grabowska et al., 2007). It was higher for plants
cultivated from 4, 6 and 8-week old transplants as compared with plants obtained
from 10-week old transplants. On the other hand, significantly higher yield was
demonstrated in plants cultivated from transplants stored in cold rooms (2°C) for
one and two weeks than in plants cultivated from non-stored transplants.