After reading this article you will learn about:- 1. Origin and Botany of Knolkhol 2. Breeding Objectives of Knolkhol 3. Breeding Methods of Knolkhol 4. Useful Donors of Knolkhol 5. Cultivar Description of Kohlrabi 6. Varieties of Knolkhol.
Origin and Botany of Knolkhol:
It has been described by the writers in ancient Rome. It developed in northern Europe in the 15th century.
The swollen edible portion is stem. Leaves are attached on this bulb like swollen structure. The conducting vessels which supply the leaves often form tough inedible tissue. In the young kohlrabi seedling the stem above the epicotyl shows primary growth in thickness, while growth in length is inhibited.
This results in the development of an aerial tuber, borne on a short stem which consists of the hypocotyl and some un-thickened internodes. The secondary growth in thickness is restricted mainly to the un-thickened basal parts of the stem. Usually petiolate and rather small leaves are arranged in a compressed spiral on the bulbous part. The tubers are green or violet and generally round to flat round.
There are also types with more elongated tubers, which are transitional to marrow-stem kale. It is biennial and plants bolt at low temperature. Therefore, breeding work is possible only under temperate conditions, for example, IARI, regional station, Katrain in Himachal Pradesh in India. Flower structure and pollination details are essentially the same as for other Brassicas.
Breeding Objectives of Knolkhol:
1. Soft, mature bulbs at edible stage
2. High yield
3. Spherical swollen bulb like stem
4. Resistance to Fusarium wilt, Xanthomonas campestris and club root (Plasmodiophora brassicae)
5. Tolerance to cold
6. Free from bolting
Breeding Methods of Knolkhol:
Normally, knolkhol is self-incompatible and therefore, cross-pollinated in nature. Mass selection/line breeding/family selection/population improvement methods/hybrid breeding could be utilised for improvement of knolkhol. For testing quality, fully mature bulbs should be examined for toughness measured as thickness of vascular tissue and the outer skin or epidermal layer.
A technique used by breeders of marrow-stem kale will provide rapid assessment of the thickness of tough (lignified) vascular tissue. A narrow wedge should be removed from the bulb and treated by immersing in a solution of phloroglucin which acts as a stain. The thickness of vascular tissue is a direct measure of toughness and will be indicated by the width of the pink zone.
Bulbs with the narrowest layers should be selected for future pollination after ensuring that the cut area has been dusted with a fungicide. The qualitative and quantitative selection should be practiced only upon bulbs of the same maturity.
Undersized bulbs may be immature due to late germination or competition in the plant bed and should not be considered for breeding work. On the other hand, large bulbs with very narrow pink zones are valuable since their growth has not reduced edibility.
Useful Donors of Knolkhol:
Club root resistance – Vienna White 1350, K 240
Black rot resistance – Szentesi Tartos, Kek
Fungal disease – Boos, Timoshenko
Resistance to Alternaria leaf spot – Szentesi Faber
Cold resistance and freedom from bolting – Weismoor, White Forcing, Knauf s Early White, Moravia
Cracking resistance – Weismoor Forcing
Cultivar Description of Kohlrabi:
There are open-pollinated and F1 hybrid cultivars. The following outlines for cultivar descriptions of kohlrabi are based on the guidelines for DUS tests produced by UPOV (1980) and as given by George (1999).
1. Seedling:
Colour of cotyledons: yellow-green, light green, dark green, blue-green or violet-green
2. Foliage:
Formation of crown: weak, medium or strong
Petiole crossing of one or two leaves: absent or present
3. Leaf:
Attitude: erect, semi-erect or horizontal
4. Leaf blade:
Size: small, medium or large
Shape: narrow ovate, ovate or broad ovate
Colour: yellow-green, grey-green or blue-green
Intensity of the colour: light, medium or dark
Shape of the tip: narrowly acute, acute, obtuse, rounded or broadly rounded
Lobing (division to or almost to midribs) : absent or very weak, weak, medium, strong or very strong
Crenation of margin: absent or very weak, weak, medium, strong or very strong
Dentation of margin: absent or very weak, weak, medium, strong or very strong
Sinuation of margin: absent or very weak, weak, medium, strong or very strong
Cupping of upper side: concave, plane or convex
Blistering: absent or very weak, weak, medium, strong or very strong
Waxiness: absent or very slight, slight, medium, strong or very strong
Colour of veins: white-green, yellow-green, pale violet or dark violet
5. Petiole:
Length: short, medium or long
Thickness: thin, medium or thick
Colour: white-green, yellow-green, pale violet or dark violet
6. Kohlrabi:
Size: small, medium or large
Shape (in longitudinal section): transverse narrow elliptic, transverse elliptic, circular or broad elliptic
Shape of apex: concave, plane or convex
Colour of skin: white-green, yellow-green, pale violet or dark violet
7. Start of harvest maturity (when 50% of kohlrabis reach 7 cm diameter): very early, early, medium, late or very late.
Start of lignification: early, medium or late
NB: The UPOV description refers to the marketable part of the plant as the ‘kohlrabi’ while many seedsmen and growers refer to it as the ‘bulb’.
8. Seed yield: About 700 kg/ha.
9. 1000 Seed Weight: About 3.2 g.
Varieties of Knolkhol:
The factors which determine the value of a knolkhol variety are earliness, productivity and resistance to bolting. Late varieties are usually higher yielding than early ones. Late varieties must keep well in storage and not become fibrous at all rapidly.
Most of the varieties that are grown have globular to somewhat flat-round tubers. According to colour, the varieties can be classified into two groups, namely, varieties with a pale green tuber and those with a purplish blue tuber. The common varieties grown in India are foreign introductions.
A few important ones are as follows:
White Vienna:
It is an early variety with dwarf plants. The leaves and the stem are medium green. Knobs are globular, smooth light green with creamy white flesh. It matures in 55-60 days after transplanting.
Early Purple Vienna:
This is also an early maturing variety, taking 55-60 days for knob formation after transplanting. The leaves are purplish. Knobs are globular round and large with purple skin and light green flesh.
Large Green:
This is a late variety with vigorous growing habit. The foliage is dark green. The knobs are also dark green and flattish round. It is adapted to Himachal Pradesh.