Heterosis and its utilization for crop improvement


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Presentation on Heterosis and their Utilization in Agri-Horti Crop Improvement:

Presentation on Heterosis and their Utilization in Agri-Horti Crop Improvement Chethana , c.k Ph.D, (GPB) UASD

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Heterosis (Hybrid vigor) Application to Increase: Productivity (yield/unit/time, 15-20% of yield advantage), and Economic returns Heterosis A universal phenomenon that F1 generation shows superiority to both parents in agronomic traits or yield It presents in all biological systems and has been exploited commercially in many agricultural crops.

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History of heterosis concept



Features of heterosis:

Features of heterosis 1. Superiority over parents: Superiority in adaptation, yield, quality, disease resistance, maturity and vigour over its parents. For yield, heterosis of 40% and above over the better parent is considered significant from practical point of view in most of crop plants. 2. Confined to F1 3. Genetic control 4. Reproducible

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5. Association with SCA Heterosis has positive association with SCA The SCA is measure of dominance variance and existence of a significant amount of dominance variance is essential for undertaking heterosis breeding programme. 6. Effect of Heterozygosity The magnitude of heterosis is associated with heterozygosity because the dominance variance is associated. The dominance effects are expected to be maximum in cross pollinated spp. and minimum in self pollinated spp. 7. Conceals Recessive Genes 8. Low Frequency

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Dominance Hypothesis This theory was proposed by Davenport (1908), Bruce (1910) and Keeble and Pellew (1910). According to this hypothesis, heterosis is the result of the superiority of dominant alleles when recessive alleles are deleterious. Here the deleterious recessive genes of one parent are hidden by the dominant genes of another parent and the hybrid exhibits heterosis. AABBccdd X aabbCCDD AaBbCcDd Parent 1 With 2 dominant genes Parent 2 With 2 dominant genes Hybrid with 4 dominant genes Dominant hypothesis- An illustration

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2. Overdominance Hypothesis This theory was proposed by Shull and East in 1908. This theory is also called as stimulation of heterozygosis, cumulative action of divergent alleles, single gene heterosis, super-dominance and overdominance. According to this hypothesis, heterosis is the result of superiority of heterozygote over its homozygous parents. East in 1936 further elaborated this theory by proposing a series of alleles a1, a2, a3, a4 Combination of a1a4 will exhibit higher heterosis as compared to combinations of a1a2, a2a3, a2a4. Overdominance has been reported in barley and maize (Small in magnitude)

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Overdominace hypothesis – An illustration

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3. Epistatis It refers to interaction between alleles of two or more different loci. This is also called as non allelic interaction is of three types viz., additive X additive, dominance X dominance and additive X dominance. Epistatis , particularly that involves dominance effect (dominance X dominance) may contribute to heterosis. This has been observed in cotton and maize (Moll and Stuber , 1974).

Comparison of dominance and overdominance theories of heterosis:

Comparison of dominance and overdominance theories of heterosis Particulars Dominance Overdominance Similarities Effect of inbreeding Leads to decline in vigour Leads to decline in vigour Outbreeding Restores the vigour Restores the vigour Parental diversity Heterosis associated with parental div. associated with parental diversity Control Heterosis controlled by genes Controlled by genes Difference Cause of heterosis Heterosis result due to masking effect of dominant desirable alleles oer harmful recessive alleles Heterosis results due to complementation between divergent alleles

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Physiological basis of Heterosis

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Later growth stage

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Biochemical basis of Heterosis

Fixation of heterosis:

Fixation of heterosis Asexual Reproduction Apomixis Balanced lethal system Polyploidy

Factors affecting heterosis:

Factors affecting heterosis Mode of pollination Genetic Diversity of parents Genetic base of parents Adaptability of parents

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How to Measure Heterosis? Mid-Parent (MP) heterosis (F1 performs better than mean of two parents): F1-MP MP X100 Better Parent (BP) heterosis (F1 performs better than better parent): Standard*/Useful/Economic heterosis (F1 performs better than the check variety) : F1-BP BP X100 X100 F1-CK CK * Standard heterosis is the most useful term in commercial crop production F1-SH SH X100 Or

Inbreeding depression:

Inbreeding depression It refers to decrease in fitness and vigour due to inbreeding. The degree of inbreeding is measured by inbreeding co-efficient.

Difference between inbreeding and heterosis:

Difference between inbreeding and heterosis Inbreeding results from matings between closely related individuals, whereas heterosis resultw from crossig between unrelated strains. IBD is the decline in fitness and vigour with decreased heterozygosity , whereas heterosis increase in fitness and vigour with increased heterozygosity . IBD results due to fixation of unfavourable recessive genes in F2, while in case of heterosis the unfavourable recessive genes of one line (Parent) are the covered by favourable dominant genes of other other parent. The heterosis will be highest when some alleles are fixed in one parent other alleles in the other parent. The genes with lack of dominance will not exhibit heterosis in F1 but may show increase in performance in F2 due to fixation of genes i.e. additive action. If some genes have dominance in one direction and some in other directionthere will be no heterosis due to mutual cancellation effects of such genes.

Heterosis breeding:

Heterosis breeding Development of hybrid varieties for genetic improvement of yield is referred to as heterosis breeding. Factors important for commercial exploitation of heterosis Enough magnitude of heterosis High percentage of outcrossing Floral biology Availability of MS and SI system

Hybrid varieties:

Hybrid varieties The progeny of a cross between genetically different plans is called hybrid. Hybrid is F1 generation of mating between genetically dissimilar plants. The F1 population that are used for commercial cultivation are referred to as hybrid varieties. The hybrid varieties are developed to exploit the heterosis or hybrid vigour.

Main features of hybrids:

Main features of hybrids Productivity Genetic constitution Adaptability Application Resistance

Types of hybrid:

Types of hybrid 1. Intraspecific Hybrid A hybrid between genetically different genotype of the same spp. a. Single cross hybrid A x B F1 (SCH) b. Three way cross hybrids ( AxB) x C F1 (TCH) c. Double cross hybrid ( AxB) x (CxD) F1 (DCH) d. Double top cross ( AxB) x OPV F1 (DTCH) e. Multiple cross f. Polycross

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2. Interspecific Hybrid The F1 progeny between two different spp. of the same genus. Eg: In cotton Tetraploid cultivated spp. ( G.hirsutum X G. barbadense ) (Varalaxmi, DCH 32, DHB 105, Sruthi, HB 224, NHB 12, TCHB 213) Diploid cultivated spp. ( G.arboreum X G.herbaceum ) (DH 7, DH 9, Pha 46, and DDH 2)

Development of hybrid varieties:

Development of hybrid varieties The production of hybrid varieties in maize consists of three steps.. Development of inbreds Evaluation of inbred lines: by GCA & SCA Production of hybrid seed

Utilization of Heterosis:

Utilization of Heterosis Springer&Stupar, 2010

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Hybrid Wheat Wheat hybrids can yield up to 30% more than their parents, but hybrids with heterosis at these levels usually are the product of crosses between different classes of wheat, such as a cross of hard red winter wheat by soft red winter wheat. Commercially useful wheat hybrids must be made within a class, to maintain milling and baking quality. Crosses within a quality class typically have less heterosis, only about 5-15% more than their parents. The lower amount of heterosis may be because of relationship among members of a relatively closed gene pool. Donald N. Duvick, 1999

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Hybrid tomato Although tomato hybrids can exhibit heterosis for yield, the amount of yield increase in absence of stress is small or even non-existent. The unique utility and attraction of hybrid tomatoes is that they allow breeders to assemble, in one cultivar, complementary genes for disease resistance as well as for traits affecting product quality such as shelf life. Tomato hybrids also exhibit increased yield stability, perhaps because they have a better balance of genes for disease resistance Donald N. Duvick, 1999 Janick, 1996)

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B73 B73 X Mo17 Mo17 x B73 Mo17 Plant cell:2003

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Springer&Stupar, 2010

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Per se performance, nature and magnitude of heterosis for number of seeds per fruit in Bitter gourd hybrids Crosses Per se performance Heterosis percentage Female Male F1 MP BP CC GLA 1 x PV 29.33 21.50 26.50 4.47 -9.35 15.22** GLA 1 x IC 29.23 27.50 23.00 18.92** -21.32 0.00 GLA 1 x GLL 29.23 24.50 25.83 -3.85 -11.63 12.32 GLA 2 x PV 31.33 21.50 26.00 -15.80 -13.05* 13.09 GLA 2 x IC 31.33 27.50 29.00 -1.42 -7.45 26.09** GLA 2cx GLL 31.33 24.50 32.50 16.42* 3.72 41.35 MBTH-100 (CC) 23.00 Agasimani, 2008

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Crosses Per se performance P1 P2 F1 Mutant 40 x Mutant 406 2.6 2.5 2.7 Mutant 51 x Mutant 181 2.3 2.7 3.7 Mutant 224 x Mutant 450 2.6 3.1 3.6 Mutant 353 x Mutant 440 2.2 3.1 3.4 Mutant 353 x Mutant 699 2.2 2.6 3.0 Per se performance and magnitude of heterosis for 1000 seed weight in sesame Barurkar, 2009

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Name of the crop Type of cross Name of the varities released Maize Duoble & three way crosses Ganga 2, Ganga 5, Ganga 11, Deccan 103, Makka 1, Vl 42 etc. Pearlmillet Single cross HB 3, BJ 104, MBH 110, BK 560, MH 179 etc. Sunflower Single cross BSH 1, HSFH 1, MSFH 10, KBSH 1, KBSH 11 etc. Castor Single cross GCH 2, GCH 3, Gauch 1, GCH 4 Cucumber Single cross Pusa Sanyog Sorghum Single cross CSH 1, CSH 5, CSH 6, CSH 9, CSH 10, CSH 11 Cotton Intraspecific H4, H6, H8, H10, JKHY 1, JKHY 2, PKVHY 2, PKVHY 3, 4 Hirsutum hybrids NHH44, CICR HH 1, Savita , Surya, DHH 11, Dhanalaxmi Interspecific Varalaxmi , DCH 32, HB 224, DHB 105 Pigeonpea Single cross ICPH 8 Rice Single cross APRH 1, APRH 2 etc. Tomato Single cross Hybrid tomato Brinjal Single cross Vijaya , Pusa kranti , Arkasheel , Arkanaveet , Azad kranti Jute Single cross Hybrid C Popular hybrids released in different field crops in India

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The magnitude of yield heterosis in various crop plants Crops % Heterosis Character Authors Bajra 32.5 – 69.8 Grain yield Ahulwalia & Patnaik (1963) Brinjal 62.8 Fruit yield Mishra (1977) Castor 8.90 – 76.6 Bean yield Satyabalan et al. (1965) Cotton 2.1 – 100 Lint yield Patel & Patel (1952) Cucumber 64.2 – 78.7 Fruit yield Singh, Gill & Ahulwalia (1970) Linseed 78.1 Seed yield Dalai & Singh (1965) Maize 40 Grain yield Beal (1877-1887) 100 “ Shull (1910) Rice 23.5 – 93.5 Grain yield Purohit (1972) Sorghum 97 Grain yield Bartel (1949) Sunflower 70 Grain yield Schurter (1964) Tomato 44.4 – 55.7 Fruit yield Choudary et al. (1965) Wheat 29.1 – 72.9 Grain yield Singh & Kandola (1969)


Merits Hybrid varieties have higher yield potential as compared to synthetics, composites and OPV. Hybrid varieties are more uniform and attractive than synthetics, composites and OPV. Hybrid varieties can develop in both self and cross pollinated spp. It is possible to reconstitute the hybrid with same genotype, which is not responsible in case of composites and OPV .


Demerits Fresh seeds has to be produced every year, because in F2 the hybrid produces various types due segregation and recombination. Farmers has to purchase fresh seed every year. The seeds of hybrids are costlier than synthetics, composites and OPV’s. Cultivation of hybrids requires more input to exploit their full potential. Production of hybrids requires more technical skill and areas as compared to synthetics, composites and OPV’s.



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