टमाटर का संकर (हाइब्रिड) बीज उत्पादन
Tomato (Lycopersicum esculentus) is one of the most important vegetable crops grown extensively in the tropical and subtropical parts of the world. It is grown mainly for fresh market and to a little extent for processing. Increased attention is now being bestowed to breeding and production of tomato. Production of tomato can further be increased if improved cultural practices are combined with good quality seeds.
Hybrid tomato varieties have many advantages compared to open-pollinated varieties. Hybrids usually produce higher yields. They generally mature earlier and more uniformly. Many hybrids have better fruit quality and disease resistance. With all of these advantages, many farmers prefer to sow hybrid seeds in spite of the higher seed costs. Tomato is a typical day neutral plant.
It requires 15-20 °C temperature for fruit setting. Tomato is self- pollinated crop. Self-fertilization is favored by the position of receptive stigma within the cone anthers and the normal pendant position of the flower.
Though the stigma is receptive at the time of anthesis, anthers do not dehisce until about 24-48 hours later. Cross-pollination of tomato flowers to the extent of about 5 percent may occur through insects.
Climate and Soil
Ideal growing conditions are needed to produce high quality seed. Plant grow well at 21-25°C day and 15-20 °C night temperature. Humidity is an important factor. Humidity levels higher than 60% at the time of fruit maturity will increase disease problems. Temperature above 32°C leads to reduction in fruit-set.
Fruit set is also reduced below 15.5°C temperature due to poor pollen dehiscence. Tomato can be grown in wide range of soils from sandy to clay. The optimum soil pH is 6.5 to 8.0. To obtain good seed yield, fertile soil with efficient drainage and good water holding capacity should be require.
Selecting Parents
F1 hybrid seed production involves the crossing of two different inbred lines. Best line (yield, disease and pest resistant, more nutritive) use as a female parent. Both parents should be pure. One male plant is sufficient for pollinating four female plants. Male lines sown three weeks prior to female line.
Seedling Raising
Tomato seedlings are raised in the nursery beds. Optimum time for sowing seeds in the nursery for crop production is September-October in the plains. March- April is optimum time for summer crop in the mountain areas for raising seedlings. Seeds are sown in line on a well prepared seedbed and lightly covered with soil.
After 7-10 days of sowing the young seedlings are transplanted on the second bed at a distance of 2-3 cm in both ways. The seedbeds should be irrigated immediately after transplanting. The seedlings should be protected from strong sun and heavy rains.
Three hundred to three hundred fifty grams of urea dissolved in 30 liters of water can be sprinkled on nursery beds after about a week of transplanting the young seedlings in the second bed to get healthy seedlings. About 250-300g seeds produce sufficient seedlings to cover one hectare of land.
Isolation
The minimum isolation distance between different cultivars of tomato for seed production is relatively short. This is because of the crop's high level of self- pollination. However, minimum recommended isolation distance between different varieties varies from 50 m for foundation seed and 25 m for certified seed production.
Transplanting
Transplanting should be done with the seedlings are 20-25 days old, preferably at evening time. Spacing is 60 x 45 cm to 90 x 60 cm for female parent of hybrids and 60 x 45 cm for male parent of hybrids.
Training, Pruning and Staking
Training of tomato plants with the help of wires or strings is claimed to result in early ripening, higher yield of better quality fruits and seeds, lesser disease incidence, easier intercultural operation and harvesting. Pruning of side shoots and staking results in higher yield, uniform and larger fruit size.
Emasculation
Emasculation starts about 55-65 days after sowing. Sterilization of forceps, scissors and hands necessary before emasculation with 95% alcohol. Flowers from the first cluster are removed. Chose a flower buds from the second cluster which will open in two to three days.
The petals will be slightly out of the flower bud but not opened, and the corolla color is paler. Open the selected bud with sharp-pointed forceps. Then, split open the anther cone. Pull the anther cone and remove this from the bud, leaving the calyx, corolla and pistil.
Pollen collection
Early morning is the best time for pollen collection before the pollen has been shed. Anther cones is remove from the flowers and put them in suitable containers. Drying of anther cone is carried out at 30°C for 24 hours. This temperature can be maintain by using 100-watt lamp.
Pollen can also be sun-dried, but avoid drying at midday when temperature is very high. Dried pollen strain with a fine mesh screen (200-300 mesh) and store in suitable container. Fresh pollen is best for good fruit-set. When weather conditions are not suitable for pollination kept it in the freezer for about a month.
Pollination
Emasculated flowers are pollinated when colour of corolla turns bright yellow (generally two days after emasculation). Pollination done by dipping the stigma into the pollen powder or by touching the stigma with the tip of the index finger dipped in the pollen powder. Pollination is usually done 3 times weekly. Try to avoid pollination on rainy days.
Fruit Production
Maintain the following, 30 fruits for large-fruited parent, 40 fruits for medium-fruited parent and 50 or more fruits for small-fruited parent. Remove the non-hybrid fruit from female plant to avoid contamination before harvesting.
Harvesting
Tomato fruits ripen about 50-60 days after pollination, but may take longer if temperature is low. Only completely colored and matured seed fruits are harvested.
Seed Extraction
Manual Extraction
Harvested ripe fruits are keep in nylon bags. Crush the fruits by trampling with feet. After crushing ferment the pulp to separate the gel mass embedding the seeds.
One day fermentation sufficient when temperature is above 25°C. If temperature is low than two days of fermentation may be needed. Fermented material put in an open plastic container for washing.
Then fill the container with water and stir the seeds to allow the pieces of flesh and skin sticking on the seeds to float. Repeat the washing with fresh water several times, until all the flesh and gel are completely removed, leaving clean seeds at the bottom.
Mechanical Extraction
Large scale seed extraction is commonly carried out by mechanical seed extractor Put ripe fruits into a mechanical seed extractor for crushing and separation of the seeds and gel from the pulp.
Seed gel mass treat with 0.7% hydrochloric acid (HCl) and stir the seed-gel mass for 40 minutes. When the seed is separated from the gel, pour the acid-treated seeds into a clean fine-mesh bag.
Wash the bag with tap water thoroughly so that no acid is left on the seeds’ surface. Place the seeds into a plastic container and fill up the container with tap water. Incline the container and remove the floating debris. Repeat the washing procedure several times until the seeds are clean.
Seed Drying
Excess water remove by using mesh bags and hang them in open air or spin dry them in a
Washing machine. Seeds spread in a container and put them in seed dryer for 3-4 days at 30 °C till 6-8% moisture retain in seeds.
Seed Packaging and Storage
Tomato seeds can be stored at least three to five years. The best containers are airtight, such as a sealed glass jar, metal can, or foil envelope. Label the container with names of the hybrid and parents, the date, and any other information which is valuable. Store seeds in a place where temperature is near to 20°C and relative humidity (RH) not exceed 30%.
Authors
Priyanka Kumawat1 and Turfan Khan2
1Ph.D. Scholar, Department of Horticulture, SKRAU-Bikaner
2Farm Manager, KVK Gudamalani, Barmer-II
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