HYBRID SEED PRODUCTION
WHAT IS HYBRID
Two improved varieties of rice in the first generation hybrids were created by artificial insemination.
Hybrid is produced by crossing between two genetically dissimilar parents. Pollen from male parent (Pollen parent) will pollinate, fertilize and set seeds in female (seed parent) to produce F1 hybrid seeds. For production of a hybrid CROSSING between two parents is important, the crossing process will results in heterosis. In self pollinated cross it is difficult to cross but in cross pollinated crops it is easier.
In nature to create genetic variability and for its wider adaptation in different environmental conditions, flowering plants has adopted many mechanisms for cross pollination. Cross-pollination results in genetic heterogeneity and show wider adaptations. Flowering plants have evolved a number of devises to encourage cross-pollination. Those mechanisms are;
1. Dicliny: Flowers are unisexual. In monoecious plants male and female flowers are borne on the same plant eg., cucurbits, maize, castor and coconut. In dioecious plants male flowers are borne on different plants eg., papaya, cannabis, mulberry.
2. Dichogamy: Time of anther dehiscence and stigma receptivity are different forcing them for cross-pollination. The time gap between the two may vary from one day to many days. In protoandry anthers dehisce earlier than the stigma receptivity eg; maize, sunflower. In protogyny stigma become recetive earlier than the anther dehisce eg., Pearl millet mirabilis.
3. Self-incompatibility: self fertilization in avoided by recognizing the self pollen by the stigma. Eg., Brassica, Petunia, Lilium .
4. Herkogamy: there is spatial separation of the anthers and stigma. Their relative position is such that self fertilization cannot occur. The stigma projects beyond the anthers and therefore pollen cannot land on stigma. Eg., Lucerne stigma is covered with a waxy film. The stigma does not become receptive until this waxy membrane is broken by visit of honeybees resulting in cross-pollination.
5. Male sterility: Absence or atropy or mis or malformed of male sex organ (functional pollen) in normal bisexual flower. Male sterility is of three types: genetic male sterility, cytoplasm sterility and cytoplasmic- genetic male sterility.
6. A combination of two or more of the above mechanisms may occur in some species. This improves the efficiency of the system in promoting cross-pollination.
Basics of hybrid seed production:
1. Breeders responsibilities:
(a) Develop inbred lines
(b) Identification of specific parental lines
(c) Develop system for pollen control
2. Major problems for breeders & producers