After reading this article you will learn about:- 1. Origin of Radish 2. Botany of Radish 3. Breeding Objectives 4. Breeding Methods 5. Cultivated Radish Types 6. Cultivar Description 7. Varieties.
1. Origin of Radish:
Radish probably originated in Europe and Asia. It has been under extensive cultivation in Egypt since long. It was introduced in England and France in the beginning of 16th century. In 1806, it was introduced in America. Radish does not exist in wild state, it is believed to have originated from R. raphanistrum which is widely distributed as weed in Europe.
2. Botany of Radish:
The edible portion of radish develops from the primary root and hypocotyl. The inflorescence is a typical terminal raceme of cruciferae. The flowers are small, usually white in colour and resemble those in cabbage and cauliflower. Sepals (four) are erect and petals (four) are clawed.
Radish is cross-pollinated due to sporophytic system of self-incompatibility. It shows considerable inbreeding depression on selfing. It is entomophilous. It is pollinated mainly by wild honey bees and wild-flower flies. Stigma receptivity is maintained up to four days after anthesis.
Selfing can be accomplished by bud-pollination. The flower buds are pollinated two days prior to opening by their own pollen be applying fresh pollen from previously bagged flowers of the same plant. Emasculation is not necessary in bud-pollination. After pollination, the buds are to be protected from foreign pollen by enclosing the particular branch bearing those buds in a muslin cloth bag.
In crossing the same technique is used as in bud-pollination except that in the crossing, the buds of the female parent are emasculated a day prior to opening and are pollinated by pollen collected from the flowers of the male parent which were also bagged before opening. The artificial pollination is done by hand by shaking the pollen over the stigma directly from the freshly opened but previously bagged buds of male parent.
When a large quantity of crossed seed is required, the roots of radish of female and male parents are planted in alternate rows, spaced 60 cm apart. Later about 3-4 days before opening of buds, the plants are covered under an insect-proof wire net or plastic cage of 22-24 mesh.
Usually 2 plants, 1 female and 1 male are covered under small cage, or sometimes a cage is used to cover 4 plants, 2 female and 2 male plants. A small honeybee colony is placed inside the cage, 3-4 days before opening of buds.
This method is followed when it is possible to rogue out the selfed or sib-mated plants in the seedling or root stage with the help of a dominant marker gene or when the male and female lines are homozygous for self-incompatibility alleles but are cross compatible.
This procedure can also be used to produce sib-mated seeds to maintain a variety under insect proof cages. However, in this case, it will be necessary to place about 20-30 plants under a cage to avoid inbreeding depression. A wire net or plastic net cage of 3mX3mX2.5m (height) with a small door on one side is convenient for this purpose.
3. Breeding Objectives of Radish:
i. Early rooting
ii. High yield
iii. White, long/stump roots with thin tap root and non-branching habit
iv. Non-pithy roots
v. Pungency of roots as per consumers’ preference
vi. Slow bolting habit
vii. Heat tolerance
viii. Drought resistance
ix. Wet tolerance
x. Resistance to alternaria blight, white rust, radish mosaic virus
xi. Tolerance to aphids
4. Breeding Methods of Radish:
This is practiced in landraces/cultivars collected from the farmers’ field. Roots are allowed to reach an over-mature stage. They are dug-up and leaves (but not growing points) removed.
Bare roots after discarding the undesirable types are immersed in a container of water. Roots which float being pithy and full of air spaces are discarded and only the large sinking roots are retained for seed production in isolation en masse. Small sinkers are also rejected.
This has been a common breeding approach in Japan. Inbred lines which are self-incompatible are produced by 5-6 generations of selfing through bud-pollination, while selfing, only the plants with desirable root shape, size, colour, and other quality considerations are advanced to the next generation.
The F1 hybrids could be:
(i) Single crosses
(ii) Three-way crosses
(iii) Double crosses
In a practical breeding programme, the recommended isolation distance is 500-1000 m to avoid outcrossing. Usually planting ratio of male and female lines is 1: 1.
5. Cultivated Radish Types:
These are of four types as described by George (1999):
1. R. sativus L. var. radicula, cultivated for its swollen hypocotyl as a field and protected crop, mainly in temperate areas of the world, although they are also cultivated in other areas.
2. R. sativus L. var. niger, the larger rooted type, cultivated mainly in Asia but still locally important in Germany.
3. R. sativus L. var. mougri, which has a relatively insignificant root but is cultivated as a vegetable in South-east Asia for its edible foliage and relatively long seed pods which are eaten raw, cooked or pickled.
4. R. sativus L. var. oleifera, the type cultivated as a fodder crop, especially in northern Europe.
All of these types described above readily cross-pollinate with each other and also with the four wild Raphanus species, R. raphanistrum, R. maritimus, R. landra and R. rostatus. The occasional purple rooted off-types found in seed stocks are either a result of cross-pollination between cultivated and wild species or an admixture of seed derived from wild types which were not rogued out during seed production.
6. Cultivar Description of Radish:
There are some hybrid cultivars of which the Japanese radish (‘Mooli’) is prominent. The following outlines for cultivar descriptions of R. sativus L. var. radicula are based on the guidelines for DUS tests produced by UPOV (1980) and described by George (1999).
1. Ploidy: diploid or tetraploid
Anthocyanin: absent or present
Size: small, medium or large
4. Foliage attachment: narrow, medium or wide
Attitude: erect, semi-erect or horizontal Length: short, medium or long
6. Leaf blade:
Shape: narrow-obovate, obovate or broad obovate, pointed or rounded
Colour: yellowish-green or greyish-green
Intensity of colour: light, medium or dark
Lobes (division to midrib): absent or present
Number of lobes: very few, few, medium, many or very many
Incisions of margin: absent or present
Predominate type of incisions of margin: sinuate, crenate, dentate or serrate
Depth of incisions of margin: shallow, medium or deep
Pubescence: slight, medium or strong
Anthocyanin coloration: absent or present
Intensity of anthocyanin coloration: weak, medium or strong
Thickness: thin, medium or thick
Width of root: thin, medium or thick
Shape: transverse elliptic, circular, elliptic, obovate, broad rectangular, rectangular, narrow rectangular, narrow, obtriangular or iciclical
Shape of crown: concave, plane or convex
Shape of base: acute, obtuse, round or flat
Coloration of skin: one coloured or bi-coloured
Colour of upper part: white, pink, red or violet
Expression of colour of upper part: vermillion, scarlet or carmine
Extent of white tip (bi-coloured radishes only): very small, small, medium, large or very large
Thickness of cortex: thin, medium or thick
Colour of flesh: translucent or opaque
9. Petal colour (at start of flower opening): white, white and pink, white and violet, pink or violet
Tendency to become pithy: absent or very weak, weak, medium, strong or very strong
11. Time of harvest maturity: very early, early, medium late or very late
12. Resistance to specific pests and/or pathogens
1. Breeder/foundation seed – 1600 m
2. Certified seed – 1000 m
Seed Production Systems:
Both ‘root-to-seed’ and ‘seed-to-seed’ systems are used. The root-to-seed is used for the biennial types especially in Europe where the roots are lifted in the late autumn, the tops taken off and the radishes are stored, usually in clamps, during the winter. It is also the method used for stock seed production of the annual types but in this case the material is re-planted immediately after selection.
In some areas of the world, especially in Asia, up to half of each steckling’s root is removed before replanting. It has been suggested that for seed production of the Japanese White cultivars this results in a higher seed yield.
The seed-to-seed system is used for final multiplication stages where inspections of the mature root are not considered necessary and is normally used only for spring sown seed crops unless the cultivar has a vernalization requirement.
Roguing Stages (Seed-to-Seed System):
1. At market maturity stage of radish. Root: relative size, shape, colour, proportions of each colour on bi-coloured cultivars, solidity.
2. At stem elongation. Remove early bolting plants and off-types according to stem colour. Remove wild radish types. Check that the remaining plants are true to type for foliage and stem characters.
3. At flower bud and very early at start of anthesis. As described for stage 2. Flower colour.
Basic Seed Production:
The root-to-seed system is used for basic seed production. When selecting plants according to their external morphology, care must be taken to ensure that those with pithy roots are rejected.
Traditionally, selected roots were examined for internal solidity by removing a small wedge of tissue with a knife, but Watts (1960) described an immersion technique which is very suitable for screening roots for solidity at or after normal market maturity and can be used to increase the length of time that they remain solid.
After selection, the plant’s leaves are twisted off (leaving the growing point undamaged) and the radish roots put in a bucket of water. Those roots with a degree of pithiness float and are discarded. The solid roots sink and are retained. The selected solid roots are then planted up and grown-on for seed production. For seed production, 2-3 kg seed is required to raise roots for planting 1 ha area. SMR is about 100.
1. Approximately 1000-1500 kg/ha
2. 100 seed weight-About 10 g.
7. Varieties of Radish:
It is the first variety of radish released by IARI, New Delhi in 1965. It is an Asiatic type suitable for sowing from middle of August to October in northern plains. Its roots are pure white, 30-35 cm long, tapering with green stem end. It matures in 50-55 days.
It is also an Asiatic variety with roots 30-45 cm long, white with green tinge on top. It is suitable for sowing in September. It takes 50-60 days for maturity.
This variety was developed at IARI, New Delhi from seeds collected from Denmark in 1966 by selfing and massing to get desired type of roots with good tolerance to high temperature and humid weather conditions. Roots are white, smooth, medium long (12.5 cm in summer and 20.5 cm in rainy season) and almost stumpy.
It is an early maturing tropical type which takes 40-45 days for attaining harvest maturity. Period of growing of this variety is fairly long from April to early September, the best season being from July to early September. It yields 200-350 q/ha depending on the season.
It is an introduction from Japan and recommended by IARI Regional Station, Katrain. Roots are 25-30 cm long, 5 cm in diameter, cylindrical and blunt at the tip, skin is pure white, smooth. Flesh is snow-white, smooth, crisp, solid and mildly pungent. Top is medium large with deeply cut leaves. It is suitable for October to December sowing.
Kalyanpur No 1:
It is selection from local material released in 1982 in Uttar Pradesh. Stem and foliage are green. Top is heavy, leaves are long, broad and less lobed. Roots are 22-23 cm long, smooth, crispy, white with green shoulder, thick and tapering.
It is temperate variety developed by hybridization between Black and Japanese White at IARI Regional Station, Katrain. It is suitable for December to February sowing in the plains when no other variety can form such good roots.
It is the only variety which can be grown throughout the year in the hills barring three winter months (November to January). Roots are 30-35 cm long, semi-stumpy, pure white with whitish green shoulder, mildly pungent, crispy and sweet flavoured. Tops are short with green cut semi-erect leaves.
This is an introduction from Japan and large quantity of imported seed is marketed in India by Pvt. sector seed companies. The roots are long, oblong white, medium pungent, white flesh is crispy and tender. It is leading OP radish for summer and fall cultivation in Japan.It has good tolerance to heat. Roots are 30-50 cm long. Roots are slightly tapered, foliage is dark green.
Developed through selection from exotic material at HPKV, Palampur. Plant top is small. Leaves are dark green and hairy with entire lamina, Roots are oblong with stump end. Top half of the root is green and lower half is creamy. Tail and flesh are pinkish.