Single Cross Hybrid Seed Production in Maize
Shailendra K Jha, Scientist (Plant Breeding) at ICAR-IARI, New Delhi
Lekshmy S, Scientist (Plant Physiology) at ICAR-IARI, New Delhi
Niharika Mallick, Scientist (Plant Breeding) at ICAR-IARI, New Delhi
Kumar Durgesh, Scientist (Plant Breeding) at ICAR-IARI, New Delhi,
Maize is the crop where most of the concepts of hybrid technology were developed. The initial idea of exploitation of single cross hybrid was demonstrated by G. H. Shull in maize. The use of SCH in crop cultivation requires a robust seed production program. The seed production of hybrid involves crossing of female/seed parent with male/pollen parent in isolation in a deliberate way under temporal or special isolation.
Isolation: Isolation is the first and foremost requirement of hybrid seed production which can be achieved through isolation by time i.e. temporal isolation or through isolation by space i.e. special isolation. In general, the temporal isolation of 10-15 days is sufficient between hybrids of same maturity group. But in case where the hybrids are differing in maturity, early maturing hybrids seed production should be planted first followed by planting of late maturing hybrid seed production. In spacial isolation, the lines are isolated by giving an isolation distance. The foundation seed production in maize needs an isolation of 400m while certified seed production needs an isolation distance of 200m. The isolation distance can be manipulated some time with help of physical barrier. The requirement of isolation is essential for large scale seed production. The small-scale seed production especially for supply of seed for evaluation trials can be produced by hand crossing, as getting large number of isolation is difficult.
Sowing: The sowing of female and male lines should be taken in a field with no same previous crop. The similar previous crop enhances the contamination through self sown seed of previous season. The male and female lines must be labeled properly to avoid any chance of misidentification. The male lines in field should be clearly marked. The female and male lines must be planted in optimum ratio to get the maximum yield of hybrid seed. The female-male ratio is dependent on pollen production ability of male line, pollen shedding duration of male line, height of female and male line, and nicking between male and female line. The common ratio used in hybrid seed production is 3:1, which can be further enhanced in certain hybrids depending upon the desirable traits of male and female parent.
Rouging: This is removal of undesirable off type plants, which can appear because of volunteer plant from previous season or contamination in parental lines. The rouging is performed at several stages starting from vegetative stage. During vegetative stage the off-type plants are removed based on phenotypic traits like leaf and stem pubescence or shoot and root pigmentation. In addition, any contrasting trait which can be observed easily can be used to identify the off-type plants. The other stages of rouging are prior to flowering or even during flowering. But during flowering, the off-type plants must be removed before pollen shedding specially from male rows.
Detasseling: This is one of the most important operation, which involves manual removal of tassel from female/seed parent in hybrid seed production plot. This is performed to prevent selfing in seed parent and it must be started at tassel emergence stage. The tassel must be removed completely and should be continued till detasseling of last female parent plant.
Pollination: In general maize seed production does not require any mean for forced pollination like rope pulling. But if required, can be done to enhance the seed setting.
Harvesting: At harvesting the male rows must be harvested first and removed from the field. The female/seed parent rows should be harvested later and off type looking cobs may be removed based on cob and seed traits.
Drying and Storage: The harvested cobs should be slow dried till optimum moisture content and must be stored under proper storage condition to maintain the quality of seed.
1. MacRobert, J.F., P.S. Setimela, J. Gethi, and M. Worku. 2014. Maize Hybrid Seed Production Manual. Mexico, D.F.: CIMMYT
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