Hybrid vigour, also called heterosis, is the increased performance of crossbred offspring compared to the parental inbred lines. When genetically distinct inbred lines are crossed, the resulting hybrids are typically more robust, productive, and taller than either parent. This increased performance over the parental lines is known as heterosis. The magnitude of heterosis is affected by the mode of pollination, genetic diversity between parents, and genetic base of the parental lines. Heterosis can be exploited through hybrid plant and animal breeding to increase yields, disease and pest resistance, and environmental stress tolerance.

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.
o Mutational true heterosis
o 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
o Dominance
o Over-dominance
 Physiological causes.
Greater initial capital hypothesis
ytoplasmic-nuclear interactions

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

11.  Biological Effects
Hybrids exhibiting heterosis show an increase in biological efficiency
o an increase in fertility
o 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

15. Thank you
Bagtec2019/900