Crossing technique for production of hybrids

Crossing technique for production of hybrids

    • In tomato the hybrid seed production is normally done by 'Emasculation and Hand Pollination'Emasculation is done before the anthers are mature and the stigma has become receptive to minimize accidental self pollination. Thus emasculation is generally done in the evening, between 4 PM and 6 PM, one day before the anthers are expected to dehisce or mature and the stigma is likely to become fully receptive.
    Tomato flower before and after emasculation
    Figure 3. Tomato flowers before and after emasculation. The anther and surrounding cap are removed to prevent self-pollination. The petals and sepals are cut to identify the flower for future pollination
    Flower for hybridization
    Figure 4. A seed producer is carefully preparing a flower for hybridization
    • Emasculate the bud by hand with the help of needle and forceps. Remove the calyx, corolla and staminal column or anthers, leaving gynoecium i.e., stigma and style intact in the flower. Emasculated flowers should be covered immediately with red coloured paper cover to protect against contamination from foreign pollen and also for easy identification of emasculated bud during dusting. Remove the red paper cover of the emasculated bud and dust the pollen gently over the stigmatic surface using cotton or camel brush, etc.,. After dusting, the emasculated flowers are again covered with white or other coloured paper cover for two to three days. Pollen collected from one male flower can be used for dusting 5 to 7 emasculated flowers.
    Emasculation of tomato
    Figures 5-8. Emasculation of tomato: selection of buds, removal of anther cone, and cutting of petal

    Tomato pollen
    Figures 9-13. Pollen is collected, dried, and prepared for making hybrid crosses

    Pollination of emasculated flowers

    Figures 14-16. Pollination of emasculated flowers

    Ripening seed crop
    Figure 17. Ripening seed crop
    • However use of chemical hybridizing agents (MH 1000 ppm) or CMS lines are also practiced.
    Harvesting and seed extraction
    • The fruits are harvested after full maturity of the fruit when turn in to red color fruits from first and last one or two harvests should not be used for seed extraction. The fruits from in between 6 7 harvest should be used for seed extraction. The seed viability is depends on the method on which the seeds were extracted and hence, it is more important to choose proper methods of seed extraction. Before seed extraction, the fruits are to be graded for true to type and selection of medium to large size fruits for getting higher recovery of quality seeds.
    • The acid method of seed extraction is the best method for tomato seed extraction. In this method, the fruits are to be crushed into pulp and taken in a plastic containers (or) cement tank. And then add 30 ml of commercial Hydrochloric acid per kg of pulp, stir well and allow it for ½ hour. In between this duration the pulp may be stirred well for one or two times. This facilitates the separation of seed and pulp. After ½ hour, the seeds will settle down at the bottom and then the floating fraction is to be removed. The collected seeds should be washed with water for three or four times.
    Table 1. Comparison of different seed extraction methods




    Method Mix fruit pulp with water - 24 - 48 h HCl @10ml /
    Kg of pulp - 20-30 minutes
    Washing soda @ 900mg/4 l of water- equal volume – overnight soak
    Salient feature
    • Low cost.
    • Unskilled labour.
    • More time taken.
    • Low seed recovery (0.5 to 0.6 %)
    • Dull seed colour.
    • Seed borne
    • pathogens
    • Cost is more.
    • Skilled labour.
    • Lesser time.
    • High seed recovery
    (0.8 to 1 %).
    • Bright colour market value higher.
    • Seed borne pathogen removed
    • Improper washing leads to injury to seeds
    • Recovery 0.7 to 0.8 per cent.
    • Luster of the seeds will be lost.
    • Improper washing leads to injury to seeds

    • While following acid method we must use only plastic or stainless steel containers or cement tank. Care must be taken to avoid the usage of iron or zinc containers, which will affect the viability potential of the seeds and as well, damage to the containers due to chemical reaction with acid.
    • For large scale seed extraction we can use the tomato seed extractor developed by Tamil Nadu Agricultural University. The seeds extracted by this machine may again be treated with commercial Hydrochloric acid @ 2 3 ml/kg seed with equal volume of water for 3 5 minutes with constant stirring. And then seed should be washed with water for three to four times.
    • It is easy to dry the seeds extracted by acid method and also remove the fungus growth over the seed coat, thus seeds possess golden yellow colour and high vigour. The seed extracted by fermentation method posses poor vigour and off colour due to fungal activity.
    Tomato seed extraction
    Figures 19-29. Seed Extraction

    Tomato seeds dry method
    Figures 30-32. Seeds are sun-dried, spread and loosened in a flat container, then rebagged and placed into an air drier

    Tomato Seeds storage
    Figure 33. Seeds storage
    Seed cleaning and processing
    • After proper drying, the seed processing is essential. This will be helpful for maintaining high vigour and viability by way of removing immature and small seeds. In processing, we have to remove broken, immature and diseased seeds, other crop and weed seeds, mud and other inert matters. For processing tomato seeds, BSS 10 x 10 wire mesh sieve should be used.
    Tomato Seeds
    • Storage of unprocessed seeds results in poor viability. In processing, the sieves must be cleaned while changing to other variety otherwise it leads to physical admixture results in genetic contamination. Hence, utmost care must be taken during processing of seeds to maintain quality.
    Seed treatment
    • The seeds may be treated with captan or Thiram @ 4g/kg of seeds. The seeds can also be treated with halogen mixture @ 5g/kg of seed and it is a ecofriendly seed treatment.
    Storage containers
    • Seeds could able to absorb moisture from atmosphere. Hence for storing seeds in the coastal region (or) river sides we should use moisture vapour proof containers i.e., 700 gauge polyethylene bags. For seed storage every time new containers must be used.
    Seed Yield
    • 100-120 Kg/ha
    Seed Standards (variety and hybrid)
    Factors Foundation Certified
    Pure seed (mini) 98% 98%
    Inert matter (maxi) 2% 2%
    Other crop seeds (maxi) no/kg 5/kg 10/kg
    Weed seeds (maxi) None None
    Germination (mini) 70% 70%
    Moisture (maxi) 8% 8%
    For VP container 6% 6%

Last modified: Friday, 22 June 2012, 6:35 AM