Hybrid Seed Production of Maize - B.Sc. Ag Notes

Hybrid Seeds Production of Maize

Introduction Even though the hybrid seed production methods are same as that of varieties, some additional techniques have to be followed The hybrid seeds are produced by crossing female and male lines and harvesting the seeds from female line Maize hybrid seed production there is no male sterility system in female plants. The female and male parents of few maize hybrids are: Hybrid Female Male COH (M) 4 (UMI 190 x UMI 1285) UMI 112 COH (M) 5 Single cross hybrid of UMI 285 UMI 61   Suitable climate In Tamil Nadu, maize is cultivated during June – July, September – October and January – February seasons Sowing during November - December is suitable for seed production, since seed maturity stage will not coincide with rainfall. During early stage of this crop water stagnation should be avoided.   Attention Rains during seed maturation phase will cause discolouration due to fungal attack thereby seed quality is reduced.   Isolation distance Since maize is a cross pollinated crop, it is necessary to isolate seed field from other maize fields. For this isolate the hybrid seed crop from fields of other maize varieties with same seed colour by 200 m distance. And for other varieties with different seed colour give 300 m isolation distance.   Land requirement For maize hybrid seed production, well drained sandy red or black cotton soil is suitable. The selected fields should be free from volunteer maize plants.   Field preparation Plough the field five to six times to get fine tilth. Spread 12.5 tons of FYM or composted coir pith and 10 packets of Azospirilluim in the field Prepare ridges and furrows with 60 cm spacing. Ridges and furrows enable the saving of irrigation water.

 

Sowing operation

Seed rate For one hectare 5 kg female and 2 kg male line seeds are needed. Treat the seeds with Azospirillum biofertilizer as described for varieties.   Seed treatment To control seed borne pathogens of downy mildew (fungal disease) treat the seed with carbendazim or thiram at 2g kg-1 seed. One day after seed treatment with fungicide, treat the seeds with 600 g of Azospirillum with rice gruel and shade dry for 15 minutes Azosprillum treatments help in the fixation of atmospheric nitrogen in the soil and provide nourishment to the growing plants.   Sowing Ridges and furrows at 60 cm spacing is to be formed. 2 seeds per hill on the sides of ridges adopting a spacing of 25 cm between the plant is sown During sowing, a planting ratio of 4 female lines and 2 male lines (4:2) should be followed. Four female line rows should alternate with two male rows.   Border rows Sow three border rows all around the seeds field with male line seeds.   Irrigation Immediately after sowing, irrigate the field. Then given life irrigation on third day and provide subsequent irrigations depending upon the condition of the field Generally for maize, upto 30 days, less irrigation is given. Then it is necessary to irrigate once in 10 days.Smooth silk will emerge out from the cob for fertilization Smooth silk will emerge out from the cob for fertilization. During this stage, you have to irrigate so that, the silk will come out smoothly from the cob and seed setting will occur.    Fertilizer application Apply 25 tonnes of FYM per ha. Then apply inorganic fertilizers at 100 kg N, 100 kg P and 50 kg K per ha as basal dose. On 20th and 40th day after sowing, apply 50 kg N and   25 kg P as top dressing.   Micronutrient deficiency Any nutrient deficiency in maize will adversely affect the growth of the plant. Generally due to micronutrient deficiency, the yield is reduced. Zn and Mg deficiency occurs largely in leaves. You can directly seed the faded young shoot due Zn deficiency. And in between the veins of mature leaves yellow lines are seen. To overcome these deficiencies apply ZnSO4 @ 20 kg ha-1 as basal fertilizer. Mg deficiency will cause yellowish – symptoms between edges and veins of basal leaves. The whole plant will have yellowish appearance due to Fe deficiency. To over come the above deficiencies you have to broadcast the micronutrient mixture @ 62.5 ha-1 mixed with 40 kg sand, after sowing the seeds.   Weed management Take two hand weeding on 25 DAS and 45 days after sowing. After weeding, apply fertilizers as top dressing and do the earthing up operation. Herbicides can also be applied. Spraying of Atrazin 500 g mixed in 1000 lit water and life irrigation on third day control the weeds.   Roguing Rogue the off type plants as described for varieties. Do the rouging operation separately in female and male lines. Remove the male plants in female lines and female plants in male lines, plants of other varieties and off-type and diseased plants.   What is offtypes? Plant or seed deviating significantly from the characteristics of a variety as described by the breeder in any observed respect.   Attention During roguing at flowering stage, the off types should be removed away from the field immediately. Otherwise it will contaminate the silk and affect the genetic purity.

 

Plant protection

Insect control Generally insect attack is very less in maize. In young plants, only shoot fly affects the shoots. Stem borer affects the shoot on 25-30 days after sowing. The affected shoots will dry and the sizes of the cob will be reduced when the crop attains maturity. Therefore, it is necessary to apply carbofuran granules @ 7.5 kg per acre @ 2 granules per plant.   Disease control

i.            Downy mildew:  Rogue out affected plants. Spray Metalaxyl 72 WP @ 1 kg ha-1, or Mancozeb 1 kg ha-1 20 days after sowing.     ii.            Leaf spot: Spray Mancozeb or Captan 1 kg ha-1 when the disease intensity is high.

 

Detasselling

Male inflorescence of maize plant is called tassel. Removal of tassels from female plants immediately after emergence is called detasselling. Detasselling should be continued for 14 days. It is done to enable crossing of female parent with male Detasselling technique Detasselling is done by holding the stalk with left hand, a little below the tassel, taking a firm hold of the entire with the right hand and removing tassel by a steady upward pull. Entire tassel should be removed without leaving any portion within the leaf The removed tassels should be buried at the same place itself. Remove the tassels perfectly without damage to the leaves.    Attention Removed tassels should not be left on the field they may also shed the pollen causing contamination.   Harvest Judge the optimum harvesting stage as that of varieties and harvest the male and female parental lines separately. First, the male lines should be harvested fully, after the removal of cobs of male lines from the field, the female lines should be harvested. The seeds harvested from the female line is the hybrid seed.   Cob sorting Remove very small sized cobs. The cobs which show difference in seed rows, seed number and colour should be identified and removed. And the cobs with very less seeds also should be removed.   Shelling Seeds can be separated by mechanical means. For this, moisture content should be around 15% for seed and 25% for cob. After harvesting, cobs may be dried to the required moisture level before shelling. So that mechanical damage can be reduced. Seeds can also be separated from cob by beating with sticks.  If the seeds are not shelled at correct moisture level, occurrence of mechanical damage may go upto 18 per cent, which will invite fungal attack.   Seed drying After shelling, dry the seeds, Seed drier can be used for drying. During drying, air temperature should not go beyond 40°C. Likewise avoid drying under hot sun and dry seeds during the morning or evening hours under mild sun.   Seed grading Quality seed with uniform size can be obtained by size grading the seeds with 18/64" round perforated sieves.   Seed yield By adopting the above techniques, 1500 kg per ha of hybrid seed can be harvested.   Seed storage Dry the seeds to 12% moisture content and treat with Captain or Thiram 75% wettable powder @ 70 g per 100 kg seeds mixed in 500 ml water. Treated seeds packed in cloth bag can be stored for more than one year. Seeds   dried upto 8% moisture, treated with above chemicals and packed in vapour poof polyethylene bag can be stored for 1½ years. As you have learnt in the earlier lesson on varieties, seeds can be stored by treating with halogen mixture also.   Seed certification Seed certification guarantees the quality of seed as it ensures that the certified seed has the genetic, physical, physiological and seed health qualities.  Genetic purity means that the seed gives rise to a plant which conforms to the varietal characteristics of the variety. The physical purity means that the seed is free from stones, broken seeds, straw bits and leaf bits etc. Physiological quality is measured by germination and seed health envisages freedom from pest and diseases. Seed certification is being done in many stages. It starts from verifying whether seeds were obtained from authenticated source, verification of isolation distance and inspection during plant growth, flowering, harvesting, processing and bagging. Also seed samples are drawn form the seed lot and sent to seed testing lab to test whether the seeds are possessing required physical purity and germination. Then certification tag is issued. Colour of the tag is blue for certified seeds. Only those seeds harvested from fields having prescribed field standards and possessing required seed standards are certified by the Certification Agency. Seeds thus certified are offered for sales. For further details nearer seed certification office may be contacted. Field standards (Certified seed) Factor Maximum permitted (%) Off types (%) maximum 0.5 Shedding tassel (%) maximum 1.0   Seed standards (Certified seed) Factor Maximum permitted (%) Physical purity minimum 98.0% Inert matter maximum 2.0% Other crop seeds maximum 10.0/kg Other distinguishable varieties (maximum) 10.0/kg (Number) Weed seeds basal on kernel colour and texture Nil Germination (minimum) 90.0 Moisture (%) (maximum) For moisture vapour pervious 12.0% For moixture vapour poof containers (maximum) 8.0%