Agriculture Reference
In-Depth Information
habitats, on cliffs and in scrubby vegetation. The wild types produce small
bulbs, either close to the mother bulb or, in some variants, on short stolons.
Wild relatives have been successfully crossed with cultivated leeks (Kik, 2002).
There are five horticultural groups: the Leek group, the Kurrat group, the
Taree group, the Great-headed Garlic group and the Pearl Onion group.
In leeks the development of concentric, ensheathing leaf bases has been
selected so that they form long, edible 'pseudostems' at harvest (see Plate 1).
Different types vary in the length and slenderness of the pseudostem. Turkish
and Bulgarian types have long, thin pseudostems, whereas those from Western
Europe have shorter, thicker pseudostems (van der Meer and Hanelt, 1990).
Leeks do not normally bulb but, after flowering, bulb cloves frequently form in
the leaf axil at the base of the flower stalk. Leeks are tetraploids with a
chromosome number of 32. The flowers have light purple tepals and are
produced in globose umbels. Leeks are an important crop in Europe. They are
raised from seed. They are well adapted to growing in cool conditions and are
harvested throughout the winter in maritime countries of Western Europe.
Many of the older cultivars of Western Europe are being supplanted by newer,
mainly Dutch-bred, cultivars, including hybrids, which have been developed
since the 1990s (Smith and Crowther, 1995). Because leeks, in contrast to
onions, do not have specific photoperiod requirements for development,
varieties can be grown over a wide range of latitudes. The name
A. porrum
was
given to leek by Linnaeus, and this name is still quite widely used.
In kurrat the emphasis of selection has been for edible leaves, and the
pseudostem is quite short. The crop is popular in Egypt where the leaves are
repeatedly cut and harvested every 3-4 weeks over a period of up to 18
months
.
It is grown from seeds and is tetraploid, like leek, with which it is easily
crossable to give morphologically intermediate and fertile offspring. The Taree
group, which is sometimes included in the Kurrat group, is a narrow-leafed
form cultivated as a leafy condiment in northern Iran.
Great-headed garlic has the appearance of a very robust garlic plant. It
produces a large, leek-like inflorescence, but any seeds produced are sterile and
it rarely forms top-sets in the inflorescence (Jones and Mann, 1963). It is
therefore propagated from the cloves, which are like large garlic cloves. Six
large cloves typically surround the base of the flower stalk, sometimes with
smaller cloves encased in the wrapper leaves of the bulb. If the plant does not
flower, the bulb consists of a single, large clove, termed a 'round'. Great-headed
garlic is hexaploid, with a chromosome number of 48. The flavour is similar to
that of garlic (see Table 8.1) and it is often confused with garlic by gardeners.
Cultivation is reported from Greece and Egypt and through south-west Asia to
India, often on a small scale.
Pearl onion is a minor, home-garden crop in Germany which has, in the
past, been grown commercially in The Netherlands. Each plant, which is like a
small leek without a pronounced pseudostem, forms a cluster of near-spherical,
white-skinned bulbs which are summer dormant. The plants are winter hardy
