भारत में प्याज फसल की गुणवत्ता युक्त बीज उत्पादन तकनीक
Onion (Allium cepa L.) is a major bulbous crop among the cultivated vegetable crops and it is of global importance. In India it has been grown in 0.52million ha with the production of 6.5 million tones (FAO, 2002). The productivity of onion in India is 12.5 t/ha, which is much lower than the productivity of USA (41.12 t/ha). The higher productivity of onion in USA is due to the growing of the long day hybrids and op varieties. The reasons for lower productivity of onion in India could be attributed to the limited availability of quality seed and lack of development of hybrids in onion are the major limiting factors among the others.
Status of requirements and supply of quality seed of onion in India
The estimated requirement of quality seed of onion is 3120 t (assuming seed rate 6 kg/ha) during 2002 and out of that only 9.6 % of the demand is catered by public sectors organizations viz; NHRDF, NSC, ICAR institutes (IARI &, IIHR) and SAU’s). The most of the demands of he quality seed was either meet by private sectors or unorganized program or own saved seed. Therefore, it is becomes important to increase the supply of quality seed through the efficient use of the technology. On the other hand sincere efforts should be made for the developed and release of hybrids.
Potential areas for seed production:
In India, the short day types of onion is cultivated on large scale in the northern plains, central and southern part of the country expect higher hills where the long day types onion varieties like Brown Spanish and Yellow Spanish etc.are grown over a limited area. Therefore, the seed production of the short day types of onion is done in central part of the country particularly in Mandore and Khandawa region of MP, Nasik and Pune of MS and Rajcoat district of Gujarat.However, Northern state like Punjab, Haryana and Rajeshthan are not preferred by the seed industry due the sever attack of stemphylium and purple blotch and lower seed yield but there is a potential for seed production in north under delayed planting.
Land requirement for onion seed crop;
Land to be used for seed production of onion should be free from volunteer plants. Although onion can be grown nearly in all types of soil from sandy loam to heavy clay soil, but clays are not satisfactory unless well supplied with humus to lighten them. The soils pH should preferably be 6.0-6.8.
Isolation in onion seed crop:
Onion seed field shall be isolated from contaminants viz; fields of other varieties and the fields of the same variety not confirming to varietal purity requirement for certification at least 5 m for foundation seed and certified seed during months bulb production and 1000 m and 500 m for foundation and certified seed production respectively during seed production.
However, the maximum permissible limit for bulb not confirming to the varietal characteristics is 0.10 percent and 0.20 percent (by numbers) for foundation and certified seed durng mother bulb production .The maximum permissible limit of off- types is 0.1% and 0.2% for FS and CS at and after flowering during seed production.. Onion seed crop must also is isolated from any flowering multipliers types of onion and shallots.
The ratio of N: P: K applied during seedbed preparation should be 1: 2:2 but the nitrogen ratio can be increased according to the status of the soil. Very limited work has been reported on the effects of nutrition in the first year on seed production in the second year. Ahmed (1982) showed that application of N: P: K @ 150 kg ha-1 produced the largest bulbs and highest total bulb yield at the end of first year and that supplementary N application not exceeding 100 kg/ha in second year applied during anthesis enhanced seed quality. Higher levels of N increased the seed yield both at the expense of seed quality. The high K levels during bulb production were carried over to the second year and enhanced seed quality.
During, mother bulb production the deficiency of copper or manganese should not be allowed. The deficiency of copper is indicated by bulbs of poor colour with thin, fragile scales that come off in handling. Therefore, the application of 80-120 kg powdered copper sulphate control the deficiency.
Irrigation in onion seed crop:
Hawthorn (1951) found that high soil moisture in the seedling year performed high seed yields. Borgo et al. (1993) reported that water stress during bulb sprouting and beginnings of the anthesis reduce the number of umbels and flowers/plant. However, in practice, the soil surface should not be continuously wet because it will predispose the crop to infection to root rot/damping off.
The methods of irrigation also greatly influence the seed yield and seed quality of onion. Tomar et al. (2004) observed that drip method of irrigation gave higher seed yield (894.94 q/ha) than the surface irrigation (648.94 q/ha) in onion cv. Pusa Madhvi. The seed vigour index is also higher in drip (876.49) than surface (663.71) irrigation in onion cv. Pusa Madhvi
Floral biology and pollination in Onion:
Anthesis occurs in early morning (6-7 hrs). Anther dehiscence is between 7.00 and 17.00 hr and on next day also with peak between 9.30 and 17.00 hr. Pollen fertility is highest on the days of anthesis. Stigma receptivity is also high on the day of anthesis (Jones, 1933). The duration of anthesis is approximately 4 weeks on individual umbel. The anthesis begins from outer flowers and goes centerally in succession. The flower is protandrous in nature and stigma becomes receptive when shedding of pollen is over. Onion is cross- pollinated in nature and bees, flies and other insects do pollination. It is essential to ensure that there is sufficient population of pollinating insects to achieve the full potential of onion seed. It is also possible in some situation to encourage the development of increased blowfly population by distributing suitable carrier or dried fish among the flowering crop (Currah and Proctor, 1990).
Method of seed production in Onion crop :
There are two methods of seed production in onion crop. The seed to seed and bulbs to seed methods and both the methods are in use in onion seed production. But bulb to seed method is most commonly used method of seed production.
a) Bulb to seed method of onion seed production:
In this method, the seed is sown in raised bed at 4-5 cm spacing for raising the seedling. The seedlings of 12-15 cm length are transplanted and this height attained 7-8 weeks after the seed sowing. Thus, 6-8 kg seed ha-1 is sown. The seedlings are transplanted in previously developed beds in 15x10 cm spacing. The weedicides (Stomp) is sprayed after the transplanting and followed by irrigation to check the growth of the weeds in early crop growth stage. The recommended cultural practices followed to raise healthy bulb crop.
The bulb are lifted when the 75% plant show neck fall/top die down. The bulbs are dried/curing under naturally ventilated place then neck is trimmed leaving 2-3 cm attached with bulb. The bulbs are roughed at this stage based upon the colour, shape and size. The damaged, twin bulbs and long necked bulbs if any are discarded. The medium size bulbs weighing (50-80 g) bulbs are selected and stored. The bulbs are and examined again before replanting in the following season.
One hectare of bulbs from the first year will plant3-5 ha for the seed production,. The bulbs selected for seed production and usually referred to as mothers bulbs. However, the area coverage is greatly affected by storage method and losses occur during storage. The storage temperature also influences seed yield. The temperature ranging from 4.5 to 140C with an optimum of about 120C is the best for the storage of mother bulbs that are to be planted for seed production. The plants from such bulbs produce early and heavy yield than those grown from bulbs that have been stored at higher or lower temperature. The roots of the bulbs should be left intact after harvest.
The 1\3 parts of the bulb are cut before planting to examine the number of glumes, which is related to the compactness, and shape of the bulbs. More the number of glumes flatten the shape and poor the storability. To avoid rotting due to fungal infection of the bulb in field, Bavistin 10 gm in 10 lit of water is used for dipping the bulbs before planting. This should be practice in NS/BS seed production
b) Seed to seed method of onion seed production:
In this method seedlings are transplanted in first week of October and allow over-wintering at the same place and allowing bolting (flowering). The seed are threshed from the mature umbel. This method does not allow to examine the mature bulb characters and field is rogued for off-types. Seed to seed method is not popular, since all the variety are not suitable for annual seed production due to poor bolting habit and lower seed yield. The seed produced in this method is not suitable for further multiplication.
Time of planting in onion crop:
The time of planting has great impact over the seed yield and incidence of the disease. Whenever the seed crop is planted in first fortnight of October is subjected to the heavy incidence of diseases and resulting poor seed yield. Tomar and Negi (2002) has recorded the highest seed yield of 576.80 kg/ha with low incidence of diseases and better seed quality in cv. Pusa Madhavi in 15th November planting during rabi 1999. However, the higher seed yield (1251.66 kg/ha) with complete escape from the incidence of disease in cv. Pusa Red was recorded during rabi 2000.
Bulb weight and size for onion seed production
The bulb weight has markedly influenced the seed production in onion. The increases in bulb weight an increased the seed yield. Although an increase in wt. and size of bulb results in higher seed yield, but very large size bulbs (< 90 gm) if used will need a very high seed rate (60 q/ha). Large size bulbs (3-4 cm diameter) and weighing < 90 gm may seed yield 10.00 q/ha, Choudhary (1967).
Sr.Scientist, Seed Production Unit,
IARI, New Delhi