Cultivation of Radish (Raphanus sativus)

Introduction

Radish (Raphanus sativus) is an important cool-season vegetable. However, because of its diverse varietal wealth, it is now possible to grow it all the year throughout the country; but West Bengal, Bihar, Uttar Pradesh, Punjab, Asom, Haryana, Gujarat, and Himachal Pradesh are major radish producing states. Being a short-duration and quick-growing crop, it is also easily grown as a companion or intercrop between rows of other vegetables. The edible part of radish is modified root (fusiform), which develops from both primary root and hypocotyl. The pungency in radish is due to the presence of volatile isothiocyanates. Radish has a cooling effect, it prevents constipation and increases appetite. The leaves and roots are used as salad and cooked as vegetables in various ways.

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Climate and soil

Radish is best adapted to cool or moderate climates but tropical varieties can tolerate the higher temperatures. The seeds germinate in 3-4 days with soil temperatures of 18-30°C and adequate soil moisture. However, the minimum and maximum temperature ranges for germination are 5-35°C. The temperature of 10-15°C is optimum for proper growth and development of roots, their texture, and flavor. Maximum root growth occurs initially at 20-30°C but later at 10-14°C. This is more applicable to temperate (European) varieties than the tropical (Asiatic) ones. Temperature above 25°C favors more foliage growth. The acclimatized varieties are grown in India, especially long-rooted, can withstand heat and rain much better than the European types. The high temperature causes pithiness, pungency, bitterness, and hollow root before reaching the harvestable/ edible maturity. The optimum uptake of nutrients and rise in dry matter content occurs at 20-25°C. Long day photoperiod along with warm temperature triggers early bolting even prior to the proper development of roots (premature bolting), which is an undesirable trait. Normally, the plants bolt when days are 8-10 hours long. At lower temperatures, pungency in roots is reduced, and crops can easily withstand frost.

Radish can be grown almost in all kinds of soils; but being a root crop, it requires loose and friable soils, rich in organic matter. It is moderately tolerant to soil acidity (pH 6.8-5.0), and the root and shoot growth are adversely affected below pH 5.0. Sandy loam soil is best suited for early harvesting. In heavy soils, deformed roots with fibrous laterals are produced. The roots become fibrous and forked when the soils have unrotten humus with hard and stony subsoil.

Varieties

Radish varieties are broadly classified into 2 types, viz. tropical (Asiatic) and temperate (European) variety. Tropical types can produce seeds in the plains, while temperate types need chilling requirement for flowering. Hence, the seed production of later one is limited to high hills only. The characteristic features of improved popular varieties are given here.

Tropical or Asiatic variety

Arka Nishant: This variety was developed at IIHR, Bengaluru, through selection. Its roots are medium size (25 cm long), 3-4 cm in diameter, marble-white along with crisp texture and mild pungency, and resistant to pithiness, premature bolting, root branching, and forking.

CO 1: This variety was developed at TNAU, Coimbatore, through selection from RS 44. Roots are cylindrical, and white with tapering ends. It can be grown throughout the year in Tamil Nadu and requires 40-45 days to mature. It is highly susceptible to white rust and aphids. It yields 20-25 tonnes/ha.

Hisar Mooli No. 1: It was developed by CCSHAU, Hisar. Roots are long, soft, white, and straight. It is grown in September-October. It requires 50-55 days to mature.

Japanese White: It was introduced and released by IARI, New Delhi. The root is cylindrical about 20-30 cm long, 5 cm in diameter, skin white, less pungent, and flesh crisp, solid, and mildly flavored. It matures in 45-50 days. It is suitable for sowing from October to December in plains and July to December in hills.

Kalyani White: The roots are 25-30 cm long along with blunt end and uniform in size. The skin is pure white and fleshes mildly pungent. Plants have light green tops. It can be grown throughout the year except during summer. The edible maturity is attained in 45 to 50 days.

Kalyanpur No. 1: It was developed through selection from a local collection at Kalyanpur and was recommended for commercial cultivation in Uttar Pradesh. Roots are 22-25 cm long, slim white, and green-topped. It is less affected by sawflies, aphids, and white rust.

Kashi Hans (IIVR-2): It was developed through selection at IIVR, Varanasi. It is suitable for sowing from September to February, and the first harvesting can be done within 40-50 days after sowing. It can stand in the field without pithiness up to 10-15 days after edible maturity, hence favors delayed harvesting without impairing root quality. Its foliage is soft and smooth. The roots are straight and tapering, 35-40 cm long and 3.5-4.2 cm diameter.

Kashi Sweta (IIVR-1): It was developed through selection at the Indian Institute of Vegetable Research (IIVR), Varanasi, and is suitable for spring, summer, autumn, and winter season sowing. Roots become ready for harvesting in 30-35 days after sowing. The root is 25-30 cm long, 3.5-4.0 cm in diameter, straight, and tapering with a blunt tip.

Punjab Ageti: It was developed at PAU, Ludhiana. Roots are red-skinned at the top and white at the lower half, tapering, long (25.5 cm), medium thick (2.9 cm), less pungent, and smooth with few hair. It is most suitable for sowing from April to August.

Punjab Pasand: This variety was developed at PAU, Ludhiana. It is an early maturing variety. Roots are long, pure white, semi-stumped, and free from hair. It is suitable for sowing in the main season.

Punjab Safed: This variety was developed at PAU, Ludhiana. Its roots are 30-40 cm long, 3-5 cm thick, white, tapering, smooth, mildly pungent, and free of forking. It is quick growing with roots remaining edible for 10 days after attaining full size.

Pusa Chetki: It is a selection from germplasm from Denmark and is suitable for cultivation in warmer periods. Its root is medium-large (25-30 cm), stumpy, pure white, tender, smooth, and mildly pungent. It matures in 40-45 days. Since it can tolerate high temperatures, it is suitable for sowing from mid-March to August in the north Indian plains.

Pusa Desi: Pusa Desi is a local selection at IARI, New Delhi. The roots are pure white, 30-35 cm long, tapering with green stem end, pungent and heavy yielder. It matures in 50-60 days. It is suitable for sowing from mid-August to October in the northern plains.

Radish (Pusa Jamuni): The first purple fleshed, nutritionally rich radish variety. Pusa Jamuni has a distinct advantage in root size, shape, yield, and consumer preference over the existing varieties. It has a green top. It can be grown throughout the year except during summer. The edible maturity is attained in 45 to 50 days.

Kalyanpur No. 1: It was developed through selection from a local collection at Kalyanpur and was recommended for commercial cultivation in Uttar Pradesh. Roots are 22-25 cm long, slim white, and green. topped. It is less affected by sawflies, aphids, and white rust.

Radish (Pusa Jamuni): The first purple fleshed, nutritionally rich radish variety. Pusa Jamuni has a distinct advantage in root size, shape, yield, and consumer preference over the existing varieties. It has higher anthocyanins and ascorbic acid and an average yield of 50 tonnes/ha.

Radish (Pusa Gulabi): First entire pink-fleshed nutritionally rich radish variety Pusa Gulabi has medium root size, cylindrical shape, optimal yield, and consumer preference over the existing varieties. It contains high total carotenoids, anthocyanins, and optimal ascorbic acid and with an average yield of 60 tonnes/ha.

Radish (Pusa Shweta): It is characterized by medium-long, extra white, cylindrical roots suitable for sowing from September to November in North Indian plains. It takes 50-55 days to marketable maturity. The average root weight is 200 g with about 40 tonnes/ha root yield. Its roots contain 34.84 mg/100g FW ascorbic acid, 4.20°B TSS, 424.8 ppm phosphorus, 8.48 ppm calcium, 497.86 ppm sodium, and 1.94 ppm zinc.

Radish (Palam Hriday): The roots are characterized by pink hearts and green shoulders. It is crispy and free from being pithy. Rich in vitamin C. Yield potential 25 30 tonnes/ha.

Temperate or European varieties

Chinese Pink: The roots are 12-15 cm long, semi stumpy to stumpy, pink with white color towards the tip. The roots are smooth, crisp, solid, and mildly pungent along with shining red exterior root (phloem) and white interior root (xylem). The crop matures in 50-55 days. It is most suited for hills but grows well in plains with a mild climate.

Pusa Himani: It was developed at LARI Regional Station, Katrain, through hybridization between a temperate type (Black) and an Asiatic type (Japanese White). The roots are 30-35 cm long, medium-thick, tapering, white with green shoulders, flesh pure white, crisp, sweet-flavored with mild pungency. The top is short, leaves green having less hair than Japanese White. It takes 60-65 days from sowing to maturity. It has wide adaptability and is grown almost throughout the year in the hilly regions of North India.

Rapid Red White Tipped: It is a table-type variety. Its roots are smooth, small, round, bright red with a white tip (root exterior), pure white root interior, crisp and snappy. Extra early, matures in 25-30 days.

Scarlet Globe: Its roots are round, small, 2 cm in diameter, and bright red in color. The root is crisp, soft, and redroot exterior along with white root interior. It takes 25-30 days from sowing to complete root formation. Delayed harvesting results in pithiness.

Scarlet Long: The leaves are 15-20 cm long and light green. Roots are long, tapering to a point, red root exterior along with soft and white root interior. It is ready for harvesting in 30-40 days after sowing. White Icicle: It is a medium-short duration variety. which matures in 30 days. The icicle-shaped roots are straight and tapering with small tops. Root exterior is pure white along with icy-white root interior, crisp, juicy, and sweet flavored.

Cultivation

Preparation of land

The land should be prepared thoroughly by ploughing the field 3-4 times and leveling well by planking. All the stubbles of the previous crop should be removed. The surface of the soil should be kept loose for proper growth and development of roots.

Seed rate/sowing time

Radish seeds count about 80-120/g. About 10 kg of tropical types or 12-14 kg of European types seed is sufficient to grow in one hectare. It can be sown either on ridges or on flatbeds. The distance between ridges and within the rows varies according to season and varieties. Temperate varieties, which are ready to harvest in 25-30 days are given closer spacing compared with tropical types which take a longer time to mature. Seeds are sown on 23-25 cm high ridges spaced 45 cm apart. However, for European varieties, ridges are spaced closer, 20-25 cm apart. The spacing within the rows is kept 4-8 cm after thinning. Normally seeds are sown 1.5-2.5 cm deep, (while surface sowing is practiced for round cultivars) and are immediately covered with light soil. The young plants look pale when sown deeper than 3 cm and the root maturity is also delayed. The seeds germinate within 4-5 days of sowing in properly moist soils.

Being a cool-season crop, its cultivation is preferred during winter in north Indian plains. It can be grown almost throughout the year depending upon the climatic conditions. Sowing is done from September to January in plains and March to August in hills. In a mild climate, it is grown around the year but the best quality roots are produced from November and December sowings. April-June and October-December are the best sowing times for Maharashtra, while March-August for Karnataka, Tamil Nadu, and Andhra Pradesh. For a regular supply of fresh roots, sowing should be done at 10-15 days intervals. Bold seeds germinate better, producing vigorous and healthy plants.

Manuring and fertilization

Radish is a short-duration and fast-growing crop. Hence, judicious and proper use of manures and fertilizers are essential to get good yield and excellent root quality along with high fertilizer use efficiency. It requires sufficient and readily available plant nutrients. Unlike other crops, radish roots are harvested 30-50 days after sowing. The judicious application of NPK favors early vegetative growth and rapid root thickening leading to high-quality root yield. About 20 tonnes of well rotten FYM should be mixed with soil during the last tilling or at least 15 days before sowing. Depending upon the soil fertility and variety, 60-80 kg N, 50 kg P, and 50 kg of K should be applied per hectare. The complete doses of P and K and half of N should be added to the soil before sowing as basal dressing. The remaining half of N is top-dressed in 2 split doses during early plant growth and at root formation. Foliar application of urea (2%) enhances vegetative growth at the initial stage.

Boron deficiency can be managed by soil application of borax (Na, B, O,.10H₂O) @ 15-20 kg/ha before sowing. Molybdenum deficiency results in narrow and leathery leaves and growth is checked. Application of 1.2 kg/ha of sodium molybdate (Na, MoO, 2H,O) or ammonium molybdate [(NH) Mo,O 4H₂O] controls this disorder.

Irrigation

Irrigation frequency and water quantity. depends on the sowing season and available soil moisture. To encourage quick germination of seeds and early vigorous growth as well as for the production of tender roots, radish crop has to be irrigated immediately after sowing. The crop requires sufficient water right from germination to harvesting. During summer, frequent irrigation is necessary. Otherwise, the growth will be checked and roots will be pungent making them unfit for market. Irrigate the fields at the 3-4 leaves stage or when plants attain a height of 5-7 cm. Subsequent irrigations are given at 5-7 days intervals in summer and 10-15. days during winter depending on prevalent weather conditions. Care should be taken that the field should not become dry and compact which has an adverse effect on root development. Subsurface drip irrigation gives better results than surface irrigation, especially in sandy loam soils. The irrigation requirement for radish is about 210-250 mm in sandy loam soil. Moisture fluctuations (heavy application of water after a dry period) cause root cracking/splitting, slow leaf development, and contribute to hot and bitter roots.

Interculture

Being a small-seeded root crop, thinning at 15 days after sowing is a must to ensure suitable plant population and root development. An intercultural operation like weeding and hoeing are necessary at 20-25 days after sowing in mid maturity tropical group while the temperate group requires it at 15 20 days after sowing. These roots are to be covered by way of one hoeing followed by earthing up, which will take care of roots growing above soil and weeds too. The pre-emergence herbicides such as trifluralin @ 0.9 kg ai/ha, pendimethalin @ 0.75 kg ai/ha, [email protected] 1.5 kg ai/ha and alachlor @ 1.25 kg ai/ha were surface superior in controlling the weeds and enhancing the productivity of radish.

Cropping system

Generally, high cropping intensity is followed in vegetable-based cropping systems to get maximum returns. The cropping sequence of radish-tomato-bitter gourd and radish-onion-okra is practiced in north-western parts of India. Moreover, it is intercropped with potatoes. However, summer radish can be intercropped with amaranth, especially in the eastern parts of India. For the summer crops of radish, maize could be grown as an intercrop or border crop in the northern plains of India to protect it from heatwave by the favorably changing microclimate.

Growth regulators

Germination in seeds is stimulated also and is sown after soaking in a 10-20 ppm solution of NAA. The concentration of 20 ppm NAA increases edible root yield. Seed treatment with GA, (5 ppm) also gives high seed germination and more yield.

Physiological disorders

Brown heart

It is a commonly occurring disorder in radish due to boron deficiency. At first, dark spots usually appear on the thickest part of the root. The plant growth is checked and it remains stunted. The leaves are smaller than the normal, lesser in number, and later on, show variegated appearance with yellow and purplish-red blotches. The leaf stalks show longitudinal splitting. The roots remain small, showing a distorted and greyish appearance. Boron deficiency can be managed by soil application of borax 15-20 kg/ha or foliar application of borax @ 0.1%.

Pithiness

The pithiness of root is common in summer crops than in spring or autumn. It is correlated with high temperature. When harvesting is delayed, this disorder is more pronounced. It is caused by the excess application of NPK and soil moisture stress. The quality of radish is reduced destroying its commercial value. Harvesting the crop at appropriate maturity and selecting proper varieties for cultivation during summer is recommended.

Elongated root or forking

Forking is an undesirable character because it deteriorates the quality and market value. There is secondary elongating growth in the roots that gives a look of a fork-like structure to the root. Inter-varietal variation is being considered to result from the degree of secondary elongating growth. Elongated root relates closely to soil adaptation. Varieties with vigorously elongated root, short root, or round root have been selected in areas of shallow arable soil and varieties with poorly elongated root, long root, and huge roots have been cultivated in areas with deep soil conditions. The disorder is due to excess moisture during the root development of radish. It also occurs in heavy soils due to soil compactness. Undecomposed organic manure favors elongated roots in radish. It can be corrected by reducing moisture from the field by balanced irrigation and also by sowing radish in sandy loam or light soil, loose and friable in nature.

Bolting

Development of seed stalk without proper development of roots is termed as bolting. Radish is a seed vernalizing crop in response to low temperature. The degree of bolting ability has been studied because of its disadvantage in cultivation, and breeding research has been directed towards late bolting. Early bolters should be removed during seed production. Splitting: It is caused due to heavy irrigation after long dry spell and wide difference in the temperature regimes during the later stage of root development. Splitting may be a problem in large rooted varieties and sparsely sown crops.

Diseases and pests

Important diseases are Alternaria blight (Alternaria brassicae, A. brassicicola, and A. raphani), leaf spot (Cercospora carotae), white rust (Albugo candida), downy mildew (Peronospora parasitica), black rot (Xanthomonas campestris), and radish mosaic virus (RGV). Insect pests affecting the crop are aphids, flea beetle, and mustard sawfly.

Harvesting and post-harvest management

Radish should be harvested when its roots are still tender by gently holding the tops, with a twist and pulling out vertically. The edible maturity period varies from 25-45 days depending upon the cultivar. Early maturing temperate varieties mature in 25-30 days, while tropical types take 35-45 days. Manual harvesting is common in India. Delayed harvesting results in pithiness and tastes bitter, and is unfit for market. The average yield of Indian cultivars is 15-20 tonnes/ha, whereas temperate cultivars produce 5-7 tonnes/ ha root yield.

The harvested roots along with tops are properly washed, graded, and tied in bundles. About 3-6 roots are tied in a bunch depending upon the size of the roots. These bundles are loose-packed in baskets and transported to the market. Harvested roots can be stored for 3-4 days at room temperature without impairing their quality. However, it can be stored for up to 2 months in cold storage at 0 °C with 90-95% relative humidity. Radish roots are pre-cooled rapidly to 5 °C temperature to maintain their crispy texture. Water is considered the best medium to pre-cool the roots quickly. Pre-packaging and zero energy cool chamber also increase the shelf-life of radish.

Seed production

Temperate varieties of radish are biennial, requiring low temperature (0-4°C) for a period of 40-60 days to induce bolting and flowering. Seed production of these varieties is restricted to temperate hilly regions. Sowing of seed is done in September. Temperate varieties are grown during summer in the hills. Seed production of these can be done both in the summer and autumn seasons in the hills. Tropical varieties can produce seeds both in tropical and temperate regions of India. Their sowing is done in September or October. Seed production of radish is done either by seed to seed i.e. in situ or root to seed methods. It is advisable to use the root to seed method for quality seed production. In the latter method, the root stecklings are prepared by cutting the lower 2/3rd portion of the root and trimming the tops in the same proportion. The varieties should be isolated 1,000-1,600 m apart to produce true-to-type seeds. The crop is harvested when 70% of the pods turn yellow. Threshing is done after curing and drying the harvested crop. The seed is cleaned, dried, and graded properly. The average seed yield of temperate varieties is 500-600 kg/ha, while tropical varieties give higher seed yields.