370 Handbook of herbs and spices
green shafts. Length and weight of the whole shaft and of its blanched part, as well
as the chemical composition, were also affected by the cultivar.
22.3 Cultivation and production.............................................................
22.3.1 Cultivars
Basically, there are four groups of leeks based on season of maturity: (i) summer
leek; (ii) autumn leek; (iii) autumn and winter leek; and (iv) winter leek. Leek
cultivars differ significantly in growth habit which affects the final product. They
vary from long, green narrow-leaf types with long slender white stems to long wide
leaf types with thicker shorter white stems and blue green leaves (Randy Baker,
1991). Leek is a slow-growing monocotyledonous species. Leek cultivars differ from
one another mainly in such characteristics as length and diameter of the sheath part,
leaf spacing, breadth and colour of the leaf-blades, vigour, ease of bolting, and
resistance to cold. Vigorous types are best for summer production; resistance to cold
is of special importance where leeks are to be harvested throughout the winter, while
slowness to bolt permits a prolonged harvest period in the spring.
Turkish and Bulgarian types have long, thin pseudostems, whereas those from
Western Europe have shorter, thicker ones. Leek is mainly grown for the fresh market
and varieties of different earliness are demanded. Varieties with good storability are
available but cheap imports from Holland during winter dominate the market. Breeding
material includes types of different stalk lengths. Medium-stalked types with a large
leaf mass give high total yield and are thus desired by the food industry. The fresh
market prefers long-stalked types with a small leaf mass. The thickness of the stalk
is also important for the economic outcome and thick stalks are often more crispy.
Plants with blue-green leaves which are much keeled have better winter hardiness
than plants with light-green, flat leaves. Plants should have an upright growth habit
and no bulb formation. A higher dry matter content favours the cooking characteristics
but can reduce crispness.
Resistance against rust (Puccinia allii) is an important breeding objective (Leijon
and Olsson, 1999). Leek breeders look for varietal homogeneity, high yield, long
shaft, correct leaf colour, no bulb formation, resistance to cold (in winter types) and
diseases and suitability for mechanical harvesting. Leek cultivars with dark blue-
green foliage have a higher content of chlorophyll and covering of wax than those
with pale green foliage; they survive a minimum temperature of –5 ∞C and the leaves
contain more sugars (glucose, fructose and disaccharides) for conversion during
the winter. The wax layer protects leaves from attack by various insect vectors of
viruses; the cultivar Castelstar (dark green) showed only 21% incidence of leek
yellow stripe virus in comparison with 45% in the pale green cultivar Otina (Benoit
and Ceustermans, 1990).
In Germany new leek cultivars for harvesting from September to April must be
suitable for mechanical harvesting and trimming, and industrial handling. They should
produce higher yields of improved quality (length, vigour, form) than existing cultivars,
be cold resistant (down to –20 ∞C) and resistant or tolerant to yellow stripe virus. Of
the new cultivars, Kamusch is good for harvesting in early autumn and Kilima
slightly later. The most commonly grown late autumn cultivar Elefant is short and
compact but is easily damaged during mechanical trimming. The late-winter (harvested
March/April) cultivar Poros gives a 30% higher yield than Elefant, but both cultivars
suffer badly from yellow stripe virus (Kampe, 1978).