PRESENTED BY: Pawan NagarReg. no.: 04-2690-2015M.Sc.(Fruit Science)

Heterosis breeding, it’s commercial exploitation & types of

crosses

BIRD VIEW OF PRESENTATIONInbreeding

Three way CrossPoly CrossHeterosi

s

HistoryEffect

s

Dominance hypothesis

Double CrossTop Cross

Genetic Bases

Overdominance HypothesisSingle Cross Commercial

Exploitation

Hybrid

Types of

Crosses

HETEROSIS BREEDING• Heterosis : Increased vigour and fertility due to hybridization

between unrelated strains.• Inbreeding : mating between individual related by ancestry

(Close genetic relationship). • Highest degree of inbreeding is selfing.• Inbreeding depression : Loss in vigour and fertility as a result

of inbreeding (because increased homozygosity)

BE SPECIFIC…1. Heterosis2. Hybrid Vigour3. Luxuriance

HISTORY OF INBREEDING

• Systematic efforts : 1700 A.D. when inbreeding became common practice in cattle breeding. Milk yield improved but with reduced fertility.

• 1876 : Darwin – published a book Cross and Self fertilization in Vegetable Crops. He concluded that progeny obtained from self-fertilization were weaker than those derived from out-crossing in maize.

• Precise information was given independently by East (1908) and Shull (1909).

EFFECTS OF INBREEDING Appearance of lethal and sublethal alleles Reduction in vigour Reduction in reproductive ability Separation of population in distinct lines Increase in homozygosity Reduction in yield

HETEROSIS Increased vigour and fertility due to hybridization between unrelated strains.

Superiority of an F1 hybrid over both parents in terms of yield or some other character.

Sometime may be it is in negative direction.

In 1673 Kolreuter first recognized Hybrid vigour in Nicotiana spp.

Beal studied performance of intervarietal hybrids in Maize between 1877 and 1882.

GENETIC BASIS OF HETEROSIS Dominance hypothesis- Davenport in 1908 Overdominance hypothesis- East and Shull in 1908

DOMINANCE HYPOTHESIS Davenport (1908) AA = Aa > aa Heterosis = masking of recessive alleles by

dominant alleles Prevention of expression harmful recessive alleles.

OVERDOMINANCE HYPOTHESIS Also known as superdominance. East and Shull (1908) Aa > AA or aa Heterozygosity is essential and cause of heterosis

COMPARISONSimilarities

1. Inbreeding produces inbreeding depression2. Outbreeding restores vigour and fertility3. Degree of heterosis is dependent upon the genetic

diversity between the parents

COMPARATIVE DIFFERENCEParticulars Dominance Overdominance

Inbreeding depression Homozygosity of recessive allele

Homozygosity itself

Heterosis is the result of

Masking of harmful effect of recessive allele

Heterozygosity itself

Phenotypes of hetero and homo-zygotes

AA = Aa > aa Aa > AA and aa

Inbreds as good as F1 Can be isolated Can’t

TYPES OF HETEROSIS Average heterosis or relative heterosis Heterobeltiosis Economic or standard or useful heterosis

MANIFESTATION OF HETEROSIS Increase yield Increased reproductive ability Increase in size and general vigor Better quality Earlier flowering and maturity Greater resist to disease and pests Greater adaptability

SO... On the basis of this concepts and Phenomena new

alternative Plant Breeding Approach is derived which is known as…..???

By East and Hayes in 1912 HETROSIS BREEDING

COMMERCIAL EXPLOITATION Degree of heterosis is considerably high in production of

Hybrid and Synthetic Variety from Cross Pollinated to Often Cross pollinated Crop species.

It can also be used in some self pollinated variety but Chief difficulty in commercial Exploitation of Heterosis in production of commercial quantity of Hybrid seed.

Cross Pollinated Crops:- Maize, Pearl millet, Sorghum, Cotton, Onion, Sunflower, Alfalfa, etc.

Self Pollinated Crops:- Rice, Wheat, etc. Vegetable Crops:- Tomato, Chillies, etc.

TYPES OF CROSSES Hybrid : First generation from a cross between two

pure lines, inbreds, open-pollinated varieties, clones or other population that are genetically dissimilar

Single cross : (A x B) Double cross : (A x B) x (C x D) Three way cross : (A x B) x Z Top cross : Inbred x open pollinated variety Polycross : Open pollination in isolation