hetrosis breeding - Breeding Of Vegetable, Tuber And Spices

The superiority of F1 hybrid over both its parents in terms of yield or some other characters or heterosis is increased vigours, growth, yield or function of a hybrid over the parents, resulting from crossing of genetically unlike organisms��The term heterosis was first coined by Shull in 1914. Generally heterosis manifested as an increase in vigour, size, growth, yield or some other characteristics. But in some cases, hybrid may be inferior to the weaker parent this is also regarded as heterosis.

1. WELCOME TO PRESENTATION ON HETEROSIS BREEDING COURSE TITLE : Breeding Of Vegetable, Tuber And Spices Shani Raj

2. The superiority of F1 hybrid over both its parents in terms of yield or some other characters or heterosis is increased vigours , growth, yield or function of a hybrid over the parents, resulting from crossing of genetically unlike organisms The term heterosis was first coined by Shull in 1914. Generally heterosis manifested as an increase in vigour , size, growth, yield or some other characteristics. But in some cases, hybrid may be inferior to the weaker parent this is also regarded as heterosis . Definition of Heterosis : Heterosis Breeding

3. Heterosis is of two types:- True heterosis ( euheterosis ) and pseudo- heterosis . 1. True heterosis : It is inherited. It can be further divided into two types: (a) Mutational true heterosis : It is the sheltering or shadowing of the deleterious, un- favourable , often lethal, recessive mutant genes by their adaptively superior dominant alleles. (b) Balanced true heterosis : It arises out of balanced gene combinations with better adaptive value and agricultural usefulness. 2. 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. Types of Heterosis :

4. Heterosis is estimated in three different ways , Mid parent heterosis   2) Better parent heterosis 3) Standard heterosis 1) Mid Parent Heterosis : When the heterosis is estimated over the mid parent i.e. mean value or average of the two parents is known as mid parent heterosis . It is also known as average heterosis or relative heterosis and calculated by using formula.                                            -      - Mid Parent Heterosis = F1-MP -----------X100                                             -                                                                                      MP             -   Where F1 is mean of F1 and  MP is mean of two parent Methods for Estimation of Heterosis

5. 2) Better Parent Heterosis : When the heterosis is estimated over the better parent is known as better parent heterosis . It is also known as heterobeltiosis and calculated by using formula:                                  -       - Heterobeltiosis =   F1-   BP                                     --------- X 100                                        -               -                        BP Where BP is mean of better parents. The term heterobeltiosis was used by Bitzer et al (1968) to describe the improvement of heterozygote over the better parent of the cross. 3) Standard Heterosis : It refers to the superiority of F1 over the standard commercial check variety. It is also called as economic heterosis or useful heterosis and calculated by using formula.                                        -  Standard Heterosis = F1 – Check                                      ------------------ X 100                                           Check    Heterosis leads to increase in yield, reproductive ability, adaptability, disease and insect resistance, general vigour , quality etc. For most of the characters, the desirable heterosis is positive. But for some characters like earliness, height in cereals and toxic substances are negative heterosis .

6. Theories of Heterosis There are two main theories which have been used to explain the mechanism of heterosis . One is the dominance hypothesis and the second is overdominace hypothesis. The epistasis is also considered to be associated with heterosis . Thus, there are three possible genetic causes of heterosis viz. 1) Dominance,  2) Over dominance  3) Epistasis       1) Dominance Hypothesis: This theory was proposed by Davenport (1908) Bruce (1910) and Keeble and Pellew (1910). This is the most widely accepted hypothesis of heterosis . According to this hypothesis, heterosis is the result of the superiority of dominant alleles, when recessive alleles are deleterious; here the deterious recessive genes of one parent are hidden by the dominant genes of another parent and the hybrid exhibits heterosis . Both the parents differ for dominant genes. AABBccdd X aabbCCDD -------) AaBbCcDd Parent 1             Parent 2                     Hybrid

7. 2) Overdominace Hypothesis: According to this hypothesis is the result of superiority of heterozygote over its both homozygous parents. Thus heterosis is directly proportional to the heterozygosis. The superiority of heterozygote over both homozygotes may arise either due to if  1) Production of superior hybrid substances in heterozygote is completely different from either of the homozygous products or due to  2) Greater buffering capacity in the heterozygote resulting from cumulative action of divergent alleles of stimulation of divergent alleles. 3) EPISTASIS: Epistasis refers to interaction between alleles of two or more different loci. It is also known as non-allelic interaction. The non-allelic interaction is of three type’s viz. additive X additive, dominance X dominance and heterosis has positive association with the presence and magnitude of non allelic interaction. Epistasis, particularly that involves dominance effects (dominance X dominance) may contribute to heterosis . This has been observed in cotton and maize. Epistasis can be detected or estimated by various biometrical models.

8. Effects and Use of Heterosis in Plant Breeding- Manifestation (Effects) of Heterosis : 1) Increase Yield: Heterosis is generally expressed as an increase in the yield of hybrid and may be measured in terms of grain, fruit, seed, leaf, tubers, etc. 2) Increased Reproductive Ability: Hybrids exhibiting heterosis show an increase in fertility or reproductive ability. 3) Increase in Size and General Vigour : The hybrids are generally more vigour , healthier and faster growing. 4) Better Quality: In many cases, hybrid show improved quality. Ex. In Onion keeping quality. 5) Earlier Flowering and Maturity: Hybrids are earlier in flowering and maturity than the parents. Ex. Tomato. 6) Greater Resistant to Disease and Pests: Hybrid exhibits a greater resistance to insect of disease than parents. 7) Greater Adaptability: Hybrids are more adopted to environmental changes than inbreds . 8) Faster Growth Rate: Hybrids shows faster growth rate than their parents but the total size may be comparable to that of the parent. 9) Increase in Number of Plant Parts: In some cases, there is an increase in the number of nodes, leaves and other plants parts, but the total plant size may not be larger.

9. Use of Heterosis in Plant Breeding: Heterosis is exploited through the development of hybrid. It is commercially exploited in seed production of cross pollinated crops like Jawar , maize, bajara , onion, and cucurbit. It has been also used in some self- pollinated species such as Rice, wheat, tomato, and brinjal , etc.

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