17. Heterosis breeding

Dr. NAVEENKUMAR K.L
Assistant Professor (GPB)

1. HETEROSIS Dr. NAVEENKUMAR K.L Assistant Professor Dept. of GPB UAHS Shivamogga

2. HETEROSIS Heterosis - refers to superiority of F 1 hybrids in one or more characters over its parents. The term hybrid vigour is used as synonym for heterosis. Heterosis differs from luxuriance. Heterosis- as increase of F 1 over parents in general vigour, yield and adaptation. Luxuriance -as increase of F 1 over parents in vegetative growth but not in yield and adaptation .

3. Hybrid vigour: According to Shull The developed superiority of the hybrids is the ‘hybrid vigour. Heterosis: The mechanism by which this superiority is developed

4. HISTORICAL ASPECTS OF HETEROSIS Heterosis concepts (Pre – Mendelian ) 1766 Kolreuter – Hybrid vigour in Nicotiana 1799 A. Knight – Principle of anti-inbreeding 1865 Mendel – Hybrid vigour in peas 1877 Darwin – Cross fertilization is beneficial 1880 Beal – First published report of 51% increase in yield over parents. 1891 Johnson – Crossing gave better off-springs. 1892 Mc Cleur – Inbreeding imparted sterility crossing imparted vigour.

5. History of Heterosis Concept 1914 Shull – Coined the term heterosis 1918 Jones – Practical utilization of heterosis. Jones 1918: Double cross. France Lamarck 1800s Correns , De vries 1900 Holland Von Tshermack Mendel Newyork . Heterozygosis (East & Hayes, 1912): Crossing produces heterozygosis , Selfing leads to Homozygosis. Hybrid Vigour (Jones, 1918): Synonymous to Shull’s Heterosis

6. Heterobeltiosis (Blitzer, 1968): Increased performance of hybrid over BP Euheterosis ( Dobzhansky , 1950): Hybrids possessed higher fitness than their parents Luxuriance ( Dobzhansky , 1950): Extreme heterosis for morpho - characters, but no fitness Positive and Negative heterosis (Powers, 1944): To include inferiority of hybrid over parents Adaptive Heterosis (MacKay, 1976): Heterosis for adaptability

7. Types of heterosis On the basis of origin and nature have 2 types: Euheterosis or true heterosis : superiority of F 1 hybrids over parents. 2 . Pseudoheterosis / luxuriance is an overexpression or quicker growth of characters in a variety or species hybrid which may not result from either masking of deleterious genes or from balanced gene combinations brought together in the hybrid . Therefore, luxuriance is a temporary and excessive vegetative overgrowth which has no adaptive significance. :

8. B. On the basis of types of estimation : Average or Relative heterosis Heterobeltiosis Useful or standard or Economic heterosis

9. Estimation of Heterosis 1. Average heterosis: It is the heterosis where F 1 is superior to mid parent value. In other words superior to average of two parents. Average Heterosis= [(F 1 – MP)/MP] x 100 Where, F 1 = Mean of hybrid              MP = Mid parental value.   (P 1 + P 2 ) where P 1 = Parent 1 and P 2 = Parent 2 This type of heterosis is of no use in agriculture since the superiority is below the better parent value

10. 2. Heterobeltiosis: When the heterosis is over the superior or better parent or Superiority of F 1 over the better parent. Heterobeltiosis= [(F 1 – BP)/BP] x 100 Where, BP = Mean value (over replications) of the Better Parent of the particular cross 3. Economic Heterosis/ Useful Heterosis: Superiority of the F 1 compared to the high yielding commercial check variety in a particular crop. Useful Heterosis= [(F 1 -CC) / CC] x 100 Where, CC = Mean of Commercial check variety. It is estimated in those crops where hybrids are already available for comparison. This type of heterosis is of practical value in plant breeding. 4. Negative heterosis: Performance of F1 inferior to better parent / mid parent value. - e.g. Duration.

11. Genetical Basis of Heterosis The genetical basis of heterosis is still following THREE hypotheses: DOMINANCE HYPOTHESIS . OVER DOMINANCE HYPOTHESIS. EPISTASIS HYPOTHESIS

12. A : Dominance hypothesis of heterosis. Heterosis is not due to heterozygosity per se Dominance Hypothesis Proposed by Davenport , ( 1907), Bruce (1910) & Keeble and Pellew (1910 ). Superiority of dominant alleles over recessive alleles . Heterosis is due to masking of deleterious recessive alleles by dominant alleles . Heterosis is directly proportional to the number of dominant genes contributed by each parent .

13. A: Dominance hypothesis of heterosis Example;

14. Objections Dominance hypothesis of heterosis Breeding homozygous individuals for all dominant genes in F 2 . F 2 Curve should be skewed towards dominant genes. Explanations Dominance of linked gene hypothesis (Jones, 1917 ): There may be linkage between some favourable dominant genes and some unfavourable recessive genes and as a result it is not possible to obtain true breeding homozygous individual for all dominant genes in F2 generation. 2. Smooth and symmetrical as yield is governed by polygenes (Collins 1921): yield governed by large number of genes or polygenes which exhibit continuous variation resulting in symmetrical distribution of genes.

15. B: Over dominance hypothesis of heterosis. Proposed by Shull and East in 1908 . Supported by East (1936) & Hull (1945 ). This theory called by various names such as stimulation of heterozygosis, cumulative action of divergent alleles, single gene heterosis , super dominance and over dominance . According to this hypothesis “ heterosis is the result of superiority of heterozygote over its both homozygous parents . Superiority of heterozygote may arise due 1. Production of superior hybrid substance in heterozygote 2. Cumulative action of divergent alleles

16. B: Over dominance hypothesis of heterosis. Example:

17. C. EPISTASIS HYPOTHESIS Epistasis refers to interaction between alleles of two or more different loci. Its also known as non-allelic interaction. Non allelic interaction is of three types viz., additive X additive, additive X dominance, dominance X dominance. Epistasis hypothesis Heterosis is mostly attributable to favorable epistatic interaction between non-allelic genes ( Powell 1944, Williams 1959)

18. Out of above three genetic hypothesis of heterosis the dominance hypothesis is most widely accepted. Over-dominance and epistasis also operate in the manifestation of heterosis.

19. Fixation of Heterosis Asexual reproduction: Sugarcane, potato, sweet potato, banana Apomixis : citrus, black berries, roses, blue grasses, Balanced Lethal System : evening primose ( oenothera spp ) Polyploidy : wheat -rye

20. Manifestation of heterosis May be in the following form. 1. Increased yield. 2. Increased reproductive ability. 3. Increase in size and vigour. 4. Better quality 5. Greater adaptability

21. Factors affecting heterosis 1. Mode of pollination- High in cross pollinated species than self pollinated species 2. 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. Thus maximum heterosis occurs at an optimum or intermediate level of parental diversity. 3. Genetic base of parents- High heterosis is associated with broad genetic basis of the parents. 4. Adaptability of parents- heterosis is associated with wide adaptability of the parents. Because there is close association between adaptability and genetic base.

22. 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

23. Instead of using CGMS lines, Detasseling the female inbred line is followed in India. Since use of CGMS line is costlier compared to Detasseling it is not followed. Crossing the inbreds of indigenous x exotic origin resulted in release of best hybrids. Indian x Indian - 24 to 43% yield increase. Indian x U.S. dent 58 % Indian dent x Caribbean Flint 47 to 54 % 1. Single cross hybrid – DMH1 (UAS, D), COH1 & 2 (TNAU) 2. Three way cross hybrids - Ganga -5 3. Double cross hybrids - COH 3 4. Double top cross hybrid - White kernel hybrids - Ganga safed 2 , Histarch , Ganga 4.

24. Single crosses A single cross is a hybrid progeny from a cross between two unrelated inbreds A x B F1 SCH Double cross hybrids A double cross hybrid is the hybrid progeny from a cross between two single crosses. (A x B) x ( C x D ) Eg. Ganga 1, Ranjit, Deccan, Ganga 3, Ganga safed,

25. The most striking advantage of single crosses over double and three way crosses is that single cross breeding is simpler and faster (SCH - homogenous). The probability of identifying two inbred lines that combine well is more than selecting for three or four inbreds. The expectation is that the best single cross has the highest yield, followed by the best three way cross and the best double cross. Double and three way crosses selected on the basis of their predicted performance using single cross data are developed and evaluated . DCH/TCH crosses require two stage testing whereas the evaluation of single crosses is a one stage process. Prediction has its limitations and there are chances of missing some good potential hybrids. The seed production cost is less in case of single hybrids. But the single cross hybrids are less stable than other two types of hybrids.

26. Modified single crosses A modified single cross is the hybrid progeny from a three way cross which utilizes the progeny from two related inbreds as the seed parent and an unrelated inbred as the pollen parent. (A x A' ) x B Three way crosses A three way cross is the hybrid progeny from a cross between a single cross and an inbred (A x B) x C Eg . Deccan 107, Deccan 109, Ganga 11, Ganga 5, Trishula Double modified single crosses A double modified single cross is the hybrid progeny from two single crosses , each developed by crossing two related inbreds (A X A') x (B x B') Modified three way hybrids A modified three way hybrid is the progeny of a single cross as female parent and another single cross between two related inbreds (A x B) x (C x C')

27. Non conventional hybrids: Advocated by CIMMYT for countries lacking effective seed industry INTERVARIETAL HYBRIDS Generated by crossing two varieties. Equivalent to synthetics and composites TOP CROSS HYBRIDS Inbred line x variety hybrids. They can be – IL x Variety, IL x Exp. Hybrid, IL x Synthetic variety and IL x Family INTER FAMILY HYBRID Progeny of crosses originating from same/ different population 4. DOUBLE TOP CROSS HYBRIDS Progeny of SC and a variety. Commercially produced in India and China