PLANT SCIENCES II

BSC-201

Search for Food Hunter-gatherer society

Primary subsistence method involves the direct collection of edible plants and animals from the wildObtained most of the food (up to 80%) from gathering rather than hunting.

Main Source Wild wheat (from German Einkorn, literally "one grain" or "a grain") – Wild einkorn: Triticum monococcum subsp. boeticum : 2n = 14; A genome – Distribution : n. Syria, s. & w. Turkey, n. Iraq, Iran

• Harvest: – hand-stripping + bag: average:2.05 kg/h – reconstructed sickle: average: 2.45 kg/h – 46% by weight of actual grain (threshing with wooden mortar and pestle + wind winnowing) – quantity: > needs for one year

• Nutritional characteristics: – Acceptable/ good– Poor milling, baking quality

• Advantages of einkorn wheat: – abundant & dependable food production– conserves better than meat

• Disadvantages:– Fragile rachis– Hulled seed

• Changes during domestication: – tougher axis – threshing ratio: wild: 46% grain > cultivated: 73% – more adaptable – more productive – wider leaves

Plant Domestication– Historical concepts

Hunter-gatherer societies tend to be relatively mobile: • to provide sufficient resources in order to sustain their population and the variable availability of

these resources owing to local climatic and seasonal conditions.

• Their population densities tend to be small in number (10-30 individuals), but these may gather together seasonally to temporarily form a larger group (100 or more) when resources are abundant.

Domestication of Plants (food security) helped mankind to establish – First farming societies – develop implements – and houses and towns

First Farming Societies (12,000-5,000 years ago)Humans began to deliberately grow crops and domesticate a range of plantsPopulation density increased, 60–100 times greater than hunter-gatherer societies,

Because cultivated land is capable of sustaining higher population densities than land left uncultivated.

The earliest place known to have lived mainly from the cultivation of crops is Jericho (Jordan River in the West Bank of the Palestinian (Fertile Crescent).

. By around 8000 BC this community, occupying a naturally well-watered region, is growing domesticated forms of wheat, soon to be followed by barley. Though no longer gatherers, these people are still hunters.

Domestication of Plants and Growing them as Crops resulted in Abundant food and consequently

Development of Jericho as the first known town, with a population of 2000 or more. A pioneering agricultural community, surrounded by other tribes dependent on gathering food, offers easy pickings which will need vigorous protection. Jerico has protective walls and a tower

The Fertile Crescent:The light of civilization first dawned in the Middle East along what is known by historians as the fertile cresent - a cresent-shaped region stretching from just south of modern-day Jerusalem then northward along the Mediterranean coast to present-day Syria and eastward through present-day Iraq then southward along the Tigris and Euphrates rivers to the Persian Gulf. Initially, the Fertile Crescent was only sparsely inhabited but around 8000 BC, it was in this fertile valley that agriculture was first believed to have been developed. Wild wheat and barley grew in abundunce and tribes of nomad hunters and herders began to settle down along the lush banks of the rivers and became the world's first farmers. Agriculture was the spark which lit the flame of civilization. Farming gave rise to social planning on a larger scale as groups of nomadic tribes settled down and joined co-operative forces. Irrigation developed as the need increased to feed and support growing populations. Soon towns were built to afford comfort and protection for these early settlers. Towns like Jericho, Jarmo, Ali Kosh, Catal Huyuk, Beidha and Hassuna were the basis of a new form of human social organization and became the foundation for the first civilization.

Introduction to Plant Improvement

• What is plant Improvement?– Selection/ development of plants with enhanced performance than the

existing genotype/ plants

• Early Plant improvement– No scientific methodologies are involved, only on the basis of field

performance

• Land Races– Varieties of crop plants whose genetic composition is shaped by

household agronomic practices and natural selection pressure over generations of cultivation

• Systematic Plant Improvement– Improvement in heredity of crops and Production of new crop

cultivars which are far better than the existing ones

Plant Breeding

– is the art and science of improving the heredity of plants for the benefit of the mankind

– The goal of Plant breeder is to change the heredity of plant in ways that will improve plant performance

This Systematic Plant Improvement is also referred to as

PLANT BREEDING

Performance of CLCV Susceptible Variety S-12 Over The Years at

PSC, Farms

41 40 40

32

37

29

22

27

10

15

20

25

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40

45

50

1987 1988 1989 1990 1991 1992 1993 1994

Yield (Mds/Ac)

3840

4341

45

28

33

15

20

25

30

35

40

45

50

1987 1988 1989 1990 1991 1992 1993

Yield (Mds/Ac)

(Tenant Area)

(Direct Area)

Why do we need plant breeding?

Plant Breeder Should Know

The person involved in Plant improvement should have efficient knowledge of

• Needs of the growers and consumers • Characteristics of the crop to be improved,

including its wild relatives• Principles of Genetics & Cytogenetics Principles• Special techniques adapted from related fields

for the solution of particular problems• Principles of field plot techniques• Principles involved in the design of experiments

and the statistical testing of data

Related Fields• Botany• Genetics• Plant Physiology• Plant Pathology• Entomology• Agronomy• Plant Biochemistry• Statistics• Computer Sciences

– Wheat variety with high yield, disease resistance, Aphid free, less moisture requirement, fertilizer responsive, early maturing, high quality

History of Plant Breeding

Pre-History– Improvement of wild wheat– Improvement of wild Corn– Improvement in wild potato– Improvement of wild rice

Before Mendel– Plant is correct unit for selection: Development of cultivars from

progeny of single plant– Screening against wilt in cotton– Reproductive systems in plants

Mendel– Laws of inheritance– New branch of science Genetics

After Mendel– Hybrid Corn– Dwarf Wheat– Dwarf rice– Strain building (synthetic) in forage

Selection

Selection/ Introduction

Selection/ IntroductionHybridizationTissue cultureBiotechnologyMAS

Basics of Plant Breeding Strategy

• Identify the morphological, physiological, pathological traits in a cultivated plant species that contribute to its adaptation, health productivity, and suitability for food, fibre or industrial products

• Search out new genes that encode for desired traits in different strains of the cultivated species and their close relatives

• Combine genes for the desired traits into an improved cultivar through traditional breeding or new biotechnological procedures

• Performance assessment of the improved breeding lines in the local environment in comparison with present cultivars

• Distribution of new cultivars that are superior to current cultivars

Aims and Objectives of Plant Improvement

• Higher yield• Better quality• Shape, size, colour, nutrition, taste, Malting, milling, baking, (cereals)

sugar contents in scane, large, fine, strong fibre in cotton, flavour in fruits

• Resistance to biotic and abiotic stresses• Crop duration early or late maturity as desired• Growth habit: height, type etc.• Winter hardiness• Lodging resistance• High fertilizer responsiveness• Easier thresh ability• Wider adaptability• Mechanised harvesting

Plant Genetic Resources• Plant germplasm

– is the genetic source material used by plant breeders to develop new cultivars

– Genotypes of particular species, collected from different sources and geographical origins, for use in plant breeding.

• Sources of Plant germplasm– Wild relatives

– Land races & primitive cultivars

– Obsolete cultivars

– Advanced breeding lines & other products of plant breeding program

– Current cultivars

• Thus the germplasm of a crop may be defined as – The sum total of hereditary material i.e. all the alleles of various

genes, present in a crop species and its wild relatives

Center of Diversity

• Area where vast genetic diversity existed for a cultivated crop species (NI Vavilov 1926)

Center of OriginNI Vavilov proposed that center of diversity for a crop is center of origin for that crop.

• primary centre of origins – Areas where crop plants were domesticated

• Secondary Centre of origin– areas where variation continued after domestication

Centers of diversity

• Chinese Centre• Indian Centre

– Indomalayan centre• Central Asiatic Centre• Near Eastern Centre• Mediterranean Centre• Ethiopian Centre• South Mexican and Central American Centre• South American Centre

– Chiloe Centre– Brazilian-Paraguayan Centre

Agencies engaged in plant breeding

• Asian vegetable Research and Development Center (AVRDC) Taiwan– Cabbage, Pepper, tomato, soybean & Mung bean

• International center for Agriculture Research in Dry Areas (ICARDA) Syria– Barley, Chick pea, faba bean, tropical forages, lentil &

wheat• International center for wheat and maize Improvement

(CIMMYT) Mexico– Maize, triticale and wheat

• International center for Tropical Agriculture (CIAT) Colombia– Dry beans, cassava, rice and tropical forages

Agencies engaged in plant breeding

• International Crop Research Institute for the Semi Arid Tropics (ICRISAT) India– Chickpea, millet, peanut, pigeon pea and sorghum

• International Institute of Tropical Agriculture (IITA) Nigeria– Cassava, cocoyam, cowpeas, lima bean, maize,

pigeon pea, rice, soybean, sweet potato, winged bean and yam

• International Potato Center (CIP) Peru– Potato and sweet potato

• International Rice Research Institute (IRRI) Phillipines– Rice

3Reproduction in crop plants

Flower Structure

Kinds of Flowers• Complete: Having all four floral parts i.e. petal, sepal, stamens, pistils

e.g. cotton tobacco, potato, cowpeas, soybean, tomato etc.• Incomplete: Lacking one or more floral organs e.g. corn, sorghum,

millet, wheat, oat, barley, rice, sugarcane etc.• Perfect: Bisexual, having both stamen and pistil in same flower. Eg.

cotton tobacco, potato, cowpeas, soybean, tomato, wheat, oat, barley, rice etc.

• Imperfect: Unisexual, having only stamen or pistil in flower– Staminate: having stamen only

– Pistillate: having pistil only

• Monoecious: having pistillate and staminate on same plant e.g. corn, cassava, castor

• Dioecious: Having pistillate and staminate flowers on different plants e.g. hemp, papaya

• Cleistogamous: Pollination and fertilization occur before opening of flower, promoting self pollination

Nuclear Cell Division• Mitosis (Equational Division) : the daughter nuclei normally receive

an exact copy of each chromosome originally present in the nucleus of the parent cell. – is the method of cell division by which new cells are formed in the

normal growth and development of plant.

– The only form of cell division associated with asexual reproduction

• Meiosis Consists of two successive divisions, first reductional (Meiosis I) and second equational (Meiosis II).– Essentially reduces chromosome number from diploid (2n) in the

megaspore mother cell to haploid number (n) in gametes.– Associated with sexual reproduction in higher plants

Length wise replication of chromosomes to form two identical sister chromatids

Appearance of spindle fibres

Homologous chromosomes• Chromosomes having genes

at corresponding loci controlling a common heredity characteristics

Crossing Over• Exchange of chromatid

segmentsSignificance of Meiosis• Maintenance of chromosome

numbers in plants• Segregation of contrasting

alleles leads to their subsequent recombination in following generation

• Crossing over provides mechanism for recombination of linked genes and hence new genetic variation.

Chromosome number in crop plants

Chapter 2

Reproduction in crop plants

Table 2.1

Types of Reproduction1. Sexual Reproduction (Union of male & female gametes)

– Crops normally Self Pollinated (4 – 5% cross pollination)• Self pollination is the transfer of pollen from an anther to stigma

of same flower or to a stigma of another flower on the same plant, or within a clone.

• Fertilization resulting from union of male & female gametes produced on the same plant is self –fertilization or autogamy

– Crops normally Cross Pollinated• Cross pollination is the transfer of pollen from an anther to stigma

of same flower or to a stigma of another flower on a different clone.

• Fertilization resulting from union of male & female gametes produced on different clones is cross–fertilization or allogamy

– Crops both Self and Cross pollinated• Usually the amount of cross-pollination exceeds that of the

normally self pollinated crops, yet does not reach that of the normally cross-pollinated e.g. Cotton ( 5 -25%) pigeon pea (5-40%), Sorghum, tobacco

Self Pollinated crops• Barley Tomato• Bean Triticale• Chickpea Vetch• Cowpea Wheat• Flax• Jute• Lentil• Millet• Mungbean• Oat• Peanut• Pea• Potato• Rice• Sesame• Soybean• Tobacco•

Cross pollinated Crops• Alfalfa Sugar beet• Cabbage Sugarcane• Carrot Sunflower• Castor Sweet potato• Cassava• Clover• Corn (maize)• Cucumber• Hemp• Mustard• Onion• Pearlmillet• Pepper• Rye• Safflower• squash

Sporogenesis• Production of microspores and megaspores is known as sporogenesis

• Microspores are produced in anthers (Microsporogenesis)– Each anther has 4 pollen sacs with numerous pollen mother cells

• Megaspores are produced in ovules (Megasporogenesis)– A single cell in each ovule differentiate into megaspore mother cell

Gametogenesis• Production of male and female gametes in microspore and megaspores

is known as gametogenesis

Male gametogenesis

2n

PMC

First MeioticDivision

Second MeioticDivision

n

nPollenMicrosporogenesis

nn

n

Microspore

n

Nucleus divides

Generative nucleus

Tube nucleus

Mitosis in the Generative nucleus

Tube nucleus

Male Gametes/sperm

Meiosis

Microgametogenesis

Female gametogenesis

2n

MMC

First MeioticDivision

Second MeioticDivision

nMegasporeMegasporogenesis

nn

Megaspore

n

Mitosis Mitosis

Meiosis

Megagametogenesis

nn

nn

Degenerate

v

Mitosis

v v

Egg cellSynergid

PolarNuclei

AntipodalCells

Megagametophyte(Embryo Sac)

• Pollen tube sends both male gametes/ sperms into embryo sac

• One male gamete/ sperm fuses with egg to form zygote. This process is known as FERTILIZATION.

• Second male gamete/ sperm fuses with two polar nuclei. The process is called triple fusion. These three nuclei together form PRIMARY ENDOSPERM NUCLEUS.

• The fusion of one male gamete with egg and fusion of second with polar nuclei is called DOUBLE FERTILIZATION.

• The fertilized egg develops into EMBRYO

• Primary endosperm nuclei divides to form many nuclei covered with cell wall, collectively called ENDOSPERM

Asexual reproduction (No union of sexual gametes)

Plants may develop either from vegetative parts of plants

(Vegetative reproduction) OR

Plants may arise from embryos that develop without fertilization (APOMIXIS)

Vegetative Reproduction– Propagation through vegetative plant parts (roots, tuber, stolons,

rhizomes, stems, leaf cutting or tissue culture)

Significance of Vegetative Reproduction• Desirable plant may be used as a variety as there is no danger of

segregation• Mutant buds/ branches or seedlings, if desirable can be multiplied

and used as varieties.• However it does not allow transfer of genes from one variety to

another variety

Apomixis (without mixing)In APOMIXIS, seeds are formed but the embryo develops without fertilization.

The resulting plants are identical to the parent plant.

APOMIXIS may be • Facultative Producing strictly maternally similar plants, • Obligate Reproducing only through apomixis, Obligate apomixis may be

– Vivipary: formation of plantlets instead of flowers, no seed is formed– Agamospermy: Formation of seed without the union of egg and sperm

nuclei.Agamospermy may be

1. Adventitious embyony: Embryo develops directly from vegetative cells of ovule and it does not involve production of embryo sac e.g. mango, citrus etc.

2. Gametophytic Apomixis: Embryo develops without fertilization from egg cell. Gametophytic Apomixis may be• Apospory: Unreduced embryo sac is produced from vegetative cells of the ovule• Diplospory: Unreduced embryo sac is produced from Megaspore Mother CellDiplospory may be

– Parthenogenesis: Embryo develops from the embryo sac without pollination– Pseudogamy: Pollination is necessary for embryo development but

fertilization of egg cell does not take place. Fertilization of the secondary nucleus takes place for endosperm development.

The endosperm can arise autonomously (Autonomous Apomixis) OR It can arise after fertilization (Pseudogamy)

Significance of Apomixis1. Apomixis allows plant breeder to fix heterosis

2. Apomixis allows for rapid multiplication and release of variety

Identification of Apomixis• When progeny is identical to mother plant• Through flow cytometery (Flow cytometer is an instrument that

can accurately measure the DNA contents of thousands of nuclei

Variation in Chromosome Number

Variation in chromosome may be of two types

1. Variation in chromosome number1.1. Euploidy/Polyploidy 1.2. Aneuploidy

2. Variation in chromosome structure 2A. Change in the amount of genetic information

1. deletions2. duplications

2B. Rearrangement of gene locations 1. inversions2. translocations

Chromosomal variation

1. Variation in Chromosome Number

Genetic variability forms the basis of plant improvement and variation in chromosome number adds to genetic variability

1.1. EUPLOID: Chromosome number is changed to exact multiple of the basic set

Polyploids are euploids in multiple of basic set of chromosome

– Diploid 2x – Triploid 3x– Tetraploid 4x– Pentaploid 5x– Hexaploid 6x– Septaploid 7x– Octoploid 8x

• EUPLOIDS may be– AUTOPLOIDS: Having Duplicate genome of same species– Autotetraploid: Having Duplicate genome of same diploid species

– ALLOPLOIDS: Having Duplicate genome of different species Allotetraploid or amphidiploid: Having Duplicate genome of different species

1.2. ANEUPLOID: Chromosome number of basic chromosome set is changed by addition or deletion of specific chromosomes

Ploidy Levels in Different crops

Species Crop Basic Chromosome Number (x)

Haploid (Gametic)

Number (n)

Somatic (Diploid) Chromosome number (2n)

Avena strigosa Oats 7 7 2n = 2x= 14

Avena barbata Oats 7 14 2n = 4x= 28

Avena sativa Oats 7 21 2n = 6x= 42

Gossypium arboreum Cotton 13 13 2n = 2x= 26

Gossypium hirsutum Cotton 13 26 2n = 4x= 26

Triticum monococum Wheat 7 7 2n = 2x= 14

Triticum turgidum Wheat 7 14 2n = 4x= 28

Triticum aestivum Wheat 7 21 2n = 6x= 42

Induction of Ploidy

• Natural Induction:May arise from

– Unreduced gametes: chromosome number is not reduced during meiosis

– Natural wide crossing following chromosome doubling

• Artificial Induction:– Environmental Shock

– Chemical • Colchicine: acts by dissociating the spindle and preventing migration of the

daughter chromosomes to poles• It is applied to meristemetic tissue, germinating seed, young seedling, root• Its action is modified or affected by temperature, concentration, and duration

of treatment

Significance of Polyploidy in Plant Breeding

• Permits greater expression of existing genetic diversity• Helps to change the character of a plant by altering number of

genomes consequently changing dosage of alleles related to particular trait

• Ployploids with uneven number of genomes (Like Triploid and Pentaploids) may result in infertility. This loss of seed production can be used to produce seedless watermelons and banana

– About 1/3 to ½ of angiosperms are polyploids– About 70% of wild species of grasses and 23% of legume family are

polyploids– Most of the natural polyploids are alloploids – All species don't exhibit vigor with increase in ploidy– Optimum ploidy level for corn is diploid as compared to tetraploid– Optimum ploidy level of banana is triploid (Seedless)– Blackberry is insensitive to ploidy level

Artificially Induced Autoploids • Easy to produce: AA doubled to AAAA• Characterized with thicker vegetative parts, increased flower size, less fertile

Characteristics of Autoploids• Genetic ratios are simpler in allotetraploid as compared to autotetraploids. Eg. A and a

alleles will result in 3 classes (AA, Aa, aa) in alloploid whereas it will result in 5 classes in case of Autoploid

• AAAA = quadruplex, AAAa= triplex, AAaa=duplex, Aaaa=simplex, aaaa=nulliplex)• Consequently recessive combinations are less in autoploids forcing breeders to grow

larger population

Autoploidy often result in • Increased size of meristemetic and guard cells• Decrease in total number of cells, • Reduced growth rate • consequently delayed flowering

Use of Autoploids• Due to more vegetative growth autoploids are more suitable in crops harvested for

vegetative parts (Forages, root crops, vegetables, flowers)• Useful vigour is obtained by doubling chromosome contents of diploid with low

chromosome numbers• Autoploids from cross pollinated crops are more successful than self pollinated crops• Bridging of ploidy levels in interspecific crosses

– Diploid treated with colchicine to produce Autotetraploid X tetraploid species

Artificially Induced Alloploids• Difficult to produce A, B first need to be hybridized and then doubled

to form AABB

• After chromosome doubling chromosome from A genome pair with it’s A genome homolog and B with B genome, with no homoeolog pairing between A and B genome.

• Homoeolog pairing is restricted by certain genes in natural alloploids like, In wheat, Ph1 present at long arm of 5B chromosome inhibits pairing of homoeolog chromosomes from A and B genomes.

• Chromosomes originating from different but similar genomes (like A & B in wheat are different but similar being part of one species) are said to be homoeolog chromosomes (having genes and arrangement of genes in common)

Uses of Alloploidy• Identifying genetic origin of polyploid plant• Producing new plant genotypes and plant species

– Production of Hexaploid (AABBRR) and Octoploid (AABBDDRR) triticale from rye (RR) and tetraploid (AABB) and Hexploid (AABBDD) wheat

• Facilitated transfer of genes from related species– Production of synthetic hybrids of wheat

– Fibre strength in cotton

– Arboreum(AA) X Thurberi (DD) chromosomes doubled to produce Allotetraploid which was further crossed to hirsutum (AADD)

– Facilitating transfer or substitution of individual or pair of chromosomes• IB can tranlocate with 1R chromosome of rye (due to homoeolog)

Variation in Chromosomal Number

1.2. Aneuploidy: Chromosome number of basic chromosome set is changed by addition or deletion of specific chromosomes

• Commonly results from nondisjunction during meiosis– Monosomy, trisomy, tetrasomy, etc.– Klinefelter and Turner syndromes are examples involving human sex

chromosomes

• Chromosome deletion lines– Nullisomy - loss of one homologous chromosome pair; 2N – 2

– Monosomy – loss of a single chromosome; 2N – 1

• Chromosome addition lines– Trisomy – single extra chromosome; 2N + 1

– Tetrasomy – extra chromosome pair; 2N + 2

Substitution Line: – Exchange of chromosome between cultivars of same species

• Wheat substitution lines

Alien Substitution Line: – Exchange of chromosome between cultivars of different species

• Wheat X Rye resulting in triticale

HAPLOIDY• HAPLOIDS: Plants having gamete number of chromosome

– Occur in nature in very low frequency

– In many species like corn, wheat, sorghum, barley, rye rice, flax, tobacco, cotton etc.

– Can be differentiated from normal diploids (due to smaller size)

– Haploidy can be efficiently confirmed by flow cytometery

– Haploidy can be less efficiently confirmed by chromosome counting

– Haploid plant can be made diploid by treating with colchicine

Procedures for Haploid Production

1. Identification and doubling of naturally occurring haploids• In corn 1/1000 grains is a haploid that arise through development of

an unfertilized egg into an embryo by parthenogenesis. Such haploid when doubled is far homozygous inbred line as compared to the one made through successive selfings

2. Interspecific or intergeneric hybridization followed by elimination of the chromosomes of the wild or distantly related species

• In barley H. Vulgare, Rice, wheat through H.bulbosum

• In wheat through maize

• In wheat through pearl millet and others

3. Anther or pollen culture• In wheat

Use of Haploids

Doubling of chromosomes results in diploids that are completely homozygous

• This homozygosity achieved in one step is of higher level than normally achieved after 6 generations of selfing

• Recessive mutants can be observed at very early stage• Selection of dominant alleles is facilitated• Suitable for mapping populations development

Breeding Self Pollinated Crops

What is a cultivar?

The cultivar (agricultural Variety) is a group of similar plants , which by structural features and performance may be identified from other groups of genetically similar plants within a species

Plant Kingdom is divided into - - - Family Genus species Variety/ cultivar experimental strain/ strain / advance line.

• The distinction of being named and distributed commercially serves to set apart the

cultivar from strain

Essential Characteristics of Cultivar1. Identity feature of identification2. Reproducibility true to type or similar progeny, easy in self pollinated crops,

difficult in cross pollinated crops.

To learn breeding behavior of an individual plant Progeny test: From the progeny test breeder learns that a superior looking plant is superior due to

its genetic make up or environmental influence: By growing progeny of selected superior plant, approves or disapprove its genetic superiority

To identify the genotype of a plantTest cross: Crossing of F1 plant to a homozygous recessive plant

To Accumulate desirable geneBack cross: Cross of a hybrid to one of its parent, Succession of back crosses helps to add a gene

Significance of Pollination Method1. Loci with identical genes (AA aa) will remain homozygous following

self pollination and 2. Loci with contrasting genes (Aa) will segregate, producing

homozygous and heterozygous progeny in equal proportionsHeterozygosity is reduced by 50% with each successive selfing thus

leading to homozygosity

S0 100% Aa

S1 25% AA 50% Aa 25% aa

S2 25% AA 12.5% AA 25%Aa 12.5% aa 25% aa

S3 37.5%AA 6.25%AA 12.5%Aa 6.25%aa 37.5%aa

S4 43.75%AA 3.125%AA 6.25%Aa 3.125% aa 43.75%aa

S5 46.875%AA 1.562%AA 3.125%Aa 1.562% aa 46.875%aa

BREEDING METHODSCrops can be improved by selectingMixture of plants, or a single plant from introduced germplasmMixture of plants, or a single plant from a local germplasmMixture of plants, or a single plant from a hybrid population

Three methods viz., introduction, selection and Hybridization are practiced for crop improvement.

1. INTRODUCTIONTransfer of a collection of seed or planting material from one ecological

zone to other. This collection of germplasm resources may be from– wild relatives– Land races– Commercial cultivars from other similar locations (local or international)– Advanced lines from research institutes (local or international)

Acclimatization: Adjustment of a species or a population to a changed environment over

a number of generations

2. SelectionMixture of plants, or a single plant, selected from germplasm

– Population for selection may be Mixed population

Two methods for selection from mixed population in self pollinated crops2.1. Mass selection

• Plants are selected and harvested on the basis of phenotypic expression (mostly qualitative traits) and seed composite. Therefore cultivars developed by mass selection are uniform for qualitative traits rather than quantitative traits further they are not progeny tested.

– Objectives of mass selection:• Purify a mixed cultivar or plant population by visually selecting plant with similar

phenotype• Develop a new cultivar by improving the average performance of the population

2.2. Pure line selection:• A pure line is a progeny descendent solely by self pollination from a single

homozygous plant. A pure line is genetically homozygous. Pure line selection refers to the procedure of isolating pure lines from a mixed population followed by progeny test

• Pure line cultivars were often developed from land races• Pure line selection does not create a new genotype and improvement is limited to the best

genotype in the mixed populationHow long a selection can remain pure? Depends on

• Seed mixture from other sources (mechanical Sources)• Natural crossing with other cultivars or breeding lines (natural pollination etc)• Mutations

– Constant rouging of off-type plants to maintain purity

3. Hybridization

• Hybridization is a breeding method that utilizes cross-pollination between genetically different parents to obtain gene recombination.

• Segregation generations are grown• Selection of pure lines having desirable traits from both the parents • Selected lines are evaluated by progeny tests to verify presence of

desirable traits• Lines proven to be superior may be increased as anew cultivar

SELECTION PROCEDURES FOLLOWING HYBRIDIZATION

1. Pedigree Selection2. Bulk Population3. Single Seed Descent4. Doubled Haploid

Pedigree Selection

• In pedigree selection, selection of desirable plants starts in F2 generation and continues in successive generation untill genetic purity is reached

• Cross Cultivar A X Cultivar B• F1 Generation: Grow 50-100 plants. Eliminate self plants• F2 Generation: Grow 2000 – 3000 plants, space planted, select

superior plants, harvest superior plant separately• F3 to F5: Grow progeny rows with seed harvested from superior

plants harvested in previous generation, – Identify superior row, then select and harvest 3-5 plants within

these rows, – normally 25 – 50 families are retained at the end of F5

generation, – Identity of plants and rows is maintained and superior traits are

recorded

Pedigree Selection Cont----

• F6 Generation: Grow families of plant rows, Uniform related families may be harvested togather and seed bulked, the separate seed lots are experimental lines/ advanced lines

• F7 Generation: Experimental lines are grown in preliminary yield trials and compared with adapted cultivars

• F8 to F10: Continue yield testing at micro and national level. Performance evaluation is recorded

• F11 and F12 generation: Increase seed of the best line and distribute as new cultivar– Sometimes early Yield testing (F3 or F4) is started

– Labour intensive

– Requires detailed record keeping

– Progeny lines with desirable genes are carried forward

– Permits the collection of genetic information

– Best suited to cereals, beans, peanut

– 12 years are required to develop new variety if one generation/year

PEDIGREEMETHOD

Bulk Population

• In bulk population, seeds harvested in F2 and successive generation are bulked and selection of desirable plants is delayed till F5 or F6 generation whenl genetic purity is reached

• Cross Cultivar A X Cultivar B• F1 Generation: Grow 50-100 plants. Eliminate self plants• F2 Generation: Grow 2000 – 3000 plants, harvest en masse and

bulk seed• F3 to F4: Grow 1/50 to 1/100 of hectare plots with bulked seed

harvested from previous generation• F5 Generation: Space plant 3000 – 5000 plants,

– Select 300 – 500 superior plants with desirable traits, harvest separately

• F6 generation: Grow progeny rows of selected plants:– Harvest 30 – 50 progenies having plants with desirable traits

Bulk Population Cont----

• F7 Generation: Grow superior progeny as experimental lines in preliminary yield trials and compared with adapted cultivars

• F8 to F10: Continue yield testing at micro and national level. Performance evaluation is recorded

• F11 and F12 generation: Increase seed of the best line and distribute as new cultivar– Early Yield testing (F3 or F4) can be started

– Simple, convenient, requires less labour– Requires no record keeping till selection generation– Easy to screen for biotic and abiotic stresses– Does not permits the collection of genetic information– Best suited to plant where it is difficult to harvest individual

plants – 12 years are required to develop new variety (one generation/year)

BulkPopulation

Method

Single seed descent

• The progenies of F2 plants are advanced rapidly through succeeding generation from single seed

• Cross Cultivar A X Cultivar B• F1 Generation: Grow 50-100 plants. Eliminate self plants• F2 Generation: Grow 2000 – 3000 plants, harvest single seed from

each plant• F3 to F4: Grow seeds harvested in previous generation, harvest

single seed from each plant• F5 Generation: Space planting from seeds harvested in previous

generation. Select superior plants with desirable traits, harvest yto collect seed from each plant separately

• F6 Generation: Grow progeny rows from plants harvested in previous generation. Harvest rows superior for desirable traits. Each row will have originated from a different F2 plant

Single Seed Descent Cont----

• F7 Generation: Experimental lines are grown in preliminary yield trials and compared with adapted cultivars

• F8 to F10: Continue yield testing at micro and national level. Performance evaluation is recorded

• F11 and F12 generation: Increase seed of the best line and distribute as new cultivar– least optimum growing conditions and time requirement (only

one seed required) hence development period may also be reduced

– Sometimes early Yield testing (F4 or F5) is started– Maximum F2 plants are retained ensuring least genetic loss– Does not requires detailed record keeping– Does not permits the collection of genetic information

SingleSeed-

DescentMethod

Doubled Haploid

• Haploid plants are generated from anthers of F1 plants or by other means and chromosomes are doubled to make doubled haploid plants

• Cross Cultivar A X Cultivar B• F1 Generation: Grow 2000 – 3000 haploid plants (from anthers) • F2 Generation: Doubling of chromosomes and harvest seed from

doubled haploid plants• F3 Generation: Grow seeds harvested from previous generation and

select superior plants with desirable traits• F4 Generation: Grow progeny and select superior lines• F5 Generation: Grow preliminary yield trials• F6 to F8 Generation: Continue yield trials• F9 & F10 Generation: Increase seed of the best line and distribute

as new cultivar– Less time consuming, less labour, less record keeping, suitable

for molecular studies

Doubled Haploid Method

• Success in hybridization program can be increase by – Selection of correct parents for hybridization

– Identifying superior plants from segregating population

– Selection of suitable selection procedure following hybridization

Backcross Breeding• The backcross is a form of recurrent hybridization by which a

desirable allele for a character is substituted for the alternative allele in an otherwise desirable cultivar.

• The adapted parent , to which the allele is being added, enters into each cross and is called the recurrent parent

• The parent with superior character that enters into the initial cross but does not enter into backcross, is termed as donor or non-recurrent parent

• In case the desired trait is recessive, selfing is done after every backcross to obtain homozygous recessive for next BC

– Donor parent is supposed to contribute only one trait, so enters only once in the backcross

– In backcross, major gene share is expected from recurrent parent, so it enters repeatedly into crosses as male parent.

• Why donor parent is always kept as female in backcross breeding?

Schematic Diagram of Backcross

Original Cross Disease Resistant Cultivar

RR

X Adapted cultivar A

rr

First Backcross F1

(Rr, 50% genes from A)

X Adapted cultivar A

rr

2nd Backcross BC1

(Rr:rr, 75% genes from A)

X Adapted cultivar A

rr

3rd Backcross BC2

(Rr:rr 87.5% genes from A)

X Adapted cultivar A

rr

4th Backcross BC3

(Rr:rr, 93.75% genes from A)

X Adapted cultivar A

rr

BC4

(Rr:rr, 96.875% genes from A)

Self Rr plants from BC4 to obtain plants homozygous for RR i.e. 1RR:2Rr:1rr

DNA marker Assisted Backcross Breeding

• Marker-Assisted backcrossing is particularly useful when phenotype of the gene(s) being transferred is not readily identifiable i.e. – Transferring recessive genes

– The phenotype is visible only after pollination

– The gene is associated with a quantitative trait that would require replicated testing

– Plant has to be destroyed to assay for the correct phenotype

Multiline Breeding

• Multiline cultivar is a composite of isolines. • Isolines: Lines that are genetically identical except for one gene.

Donor Donor Genes

# of Backcrosses

Recurrent Cultivar

Isolines Multilines

Donor 1 (R1R1) 5 A1 (rr) A1(R1R1) First isolines are developed and then these Isolines are

composite to synthesize

Multiline cultivar

Donor 2 (R2R2) 5 A1 (rr) A1(R2R2)

Donor 3 (R3R3) 5 A1 (rr) A1(R3R3)

Donor 4 (R4R4) 5 A1 (rr) A1(R4R4)

Donor 5 (R5R5) 5 A1 (rr) A1(R5R5)

• Multiline cultivar has many disadvantages– There is no genetic improvement in yield or other traits– Limited utility only under regular high incidence of disease– More labor required to maintain isolines– More time required to produce sufficient seed of each isoline

• Mixture of genetically diverse lines combined in various ways to buffer against environmental stresses are called Composites.

• Variety Blend:– A variety blend is a composite cultivar produced by mixing seed

of two or more cultivars.– It is supposed that a blend of genotype will yield consistently

higher than the pure line due to better buffer against G X E interaction over location and years

Other Breeding Procedures Practiced in self pollinated crops

• Population Improvement through– Recurrent Selection: is a population improvement procedure

designed to increase the frequency of desirable alleles for a particular quantitative character by frequent intermatings among superior genotypes within the population

– Multiple Crosses: or convergent cross is produced by crossing pairs of parents and then crossing pairs of F1s until all parents enter into a common progeny. Eight parents result in 4 F1s, 4F1s result in 2F1s and 2F1s are crossed to one F1 having all parents.

– Male-sterile Facilitated Hybridization: 1)Production of male sterile isolines through backcrossing 2)Male-sterile isolines are pollinated with a group of cultivars and resultant seed is bulked to form a composite

• Early Testing– Early generation testing allows for early identification of superior

genotypes, further that can also be used in breeding programme as parent: saving time