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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