Hybrid Vigour.pptx

Hybrid vigor

1. Hybrid Vigour

2. HYBRID VIGOUR/ HETEROSIS Definition Hybrid vigour / heterosis Is the phenomenon that causes crossbred individuals to have an increased level of performance for certain traits over and above the average performance of their straightbred parents.

3. When two homozygous inbreeds (a true breeding line obtained by continuous inbreeding) of genetically unlike constituents are crossed together, the resulting hybrids obtained from the crossed seeds are usually robust, vigorous, productive and taller than the either parents. This increased productivity or superiority over the parents is known as heterosis or hybrid vigour . Heterosis can be defined as the superiority of F1 hybrid over both the parents in terms of yield or some other character.

4. Factors affecting heterosis Mode of pollination- High in cross pollinated species than self pollinated species Genetic diversity of parents- ex. In wheat heterosis is associated with crosses of more distantly related parents. Heterosis increased with genetic divergence in morphological characters and flowering time, also with respect to geographical origin of parents. Thusmaximum heterosis occurs at an optimum or intermediate level of parental diversity

5. Genetic base of parents- High heterosis is associated with broad genetic basis of the parents. Adaptability of parents- heterosis is associated with wide adaptability of the parents. Because there is close association between adaptability and genetic base.

6. Heterosis Breeding Development of hybrid varieties for genetic improvement of yield is referred to as Heterosis Breeding. In practical plant breeding, heterosis can be fully exploited in the form of hybrids, and partially in the form of synthetics and composite varieties. Important factors in the commercial exploitation of heterosis Enough magnitude of Heterosis High percentage of outcrossing Floral biology Availability of MS and SI

7. Application of Hybrid Vigour Increasing yield and nutritive value of crop plants Increasing the growth rate Increasing the meat production Enhancing the milk yield,& egg production. Improving the performance of various animals i.e : races horses & domestic pigeons. Production of new combination of colours and scents in garden flowers Producing particular characteristics in breeds i.e : dogs,cats . And birds. Producing pest resistant and disease resistant varieties of plants and animals Producing plants and animals that tolerate wide ranges of environmental changes

8. Types of Heterosis True heterosis ( euheterosis ) -It is inherited. Mutational true heterosis Balanced true heterosis pseudo-heterosis-Crossing of the two parental forms brings in an accidental, excessive and un-adaptable expression of temporary vigour and vegetative overgrowth. It is also called luxuriance.

9. Causes of Heterosis Genetic causes Dominance Over-dominance Physiological causes. Greater initial capital hypothesis ytoplasmic -nuclear interactions

10. Effects of Heterosis Quantitative Effects Increase in size and genetic vigour Increase in yield Better quality Physiological Effects Greater resistance to diseases and pests Greater flowering and maturity Greater Adaptability

11. Biological Effects Hybrids exhibiting heterosis show an increase in biological efficiency an increase in fertility survival ability

12. Heterosis in animals Mule is a hybrid from a cross between Jack (Equus hemicus ) and Mare (Earns equus ) which has been known since ancient times for its well-known qualities of strength and stubbornness. Cross between red Sindhi breed of Indian Cattle and Jersey breed of America contams 30% more butter fat in milk. Increased pork yield in pigs, more egg laying hens, silk production in silk worms .

13. Heterosis in animals

14. Disvantage of Heterosis Greater initial capital Cytoplasmic-nuclear interactions Disease occurrence (Anthracnose is a big constraint in Big onion cultivation in Sri Lanka during Maha season, Sheath blight disease caused by Rhizoctonia solani is a serious disease in Maize cultivation

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