🌾 Breeding Methods in Plant Breeding: Types & Comparison

This lesson covers core principles and exam-focused points from this topic in plant breeding.

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The following are the methods of breeding autogamous plants.

1. Introduction

2. Selection

a) Pure line selection

b) Mass selection

3. Hybridization and selection

i) Inter varietal

a) Pedigree Method

b) Bulk Method.

c) Single Seed Descent Method.

d) Modified Bulk Method

e) Mass - Pedigree Method.

ii) Interspecific hybridization

4. Back cross method

5. Multiline varieties

6. Population approach

7. Hybrids.

8. Mutation breeding

9. Polyploidy breeding

10. Innovative techniques

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I. Plant introduction

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Definition

Taking a genotype or a group of genotypes in to a new place or environment where they

were not grown previously. Thus introduction may involve new varieties of a crop already grown

in that area, a wild relative of the crop species or totally a new crop species for that area.

E.g. a) Introduction of lRRl rice varieties..

b) Introduction of sunflower wild species from Russia

c) Introduction of oilpalm in to Tamil Nadu.

Plant introduction may be of two types. 1. Primary Introduction and 2. Secondary Introduction

1. Primary Introduction

When the introduced crop or variety is well suited to the new environment, it is directly

grown or cultivated with out any alteration in the original genotype. This is known as primary

introduction. E.g. IR. 8, IR 20, IR 34, IR 50 rice varieties; oil palm varieties introduced from

Malaysia and Mashuri rice from Malaysia.

2. Secondary Introduction

The introduced variety may be subjected to selection to isolate a superior variety or it may be

used in hybridization programme to transfer some useful traits. This is known as secondary

Introduction.E.g. In soybean EC 39821 introduced from Taiwan is subjected to selection and

variety Co 1 was developed. In rice ASD 4 is crossed with IR 20 to get Co 44 which is suited for

late planting.

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Objectives of Plant Introduction

• To introduce new plant species there by creating ways to build up new industries.E.g. Oil

palm

• To introduce high yielding varieties to increase food production. E.g. Rice and wheat.

• To enrich the germplasm collection. E.g. Sorghum, Groundnut.

• To get new sources of resistance against both biotic and abiotic stresses.

E.g. NCAC accessions to have rust resistance in groundnut. Dasal rice variety for saline

resistance.Aesthetic value – ornamentals are introduced for aesthetic value.

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Plant Introduction Agencies

Most of the introductions occurred very early in the history. In earlier days the agencies

were invaders travelers, traders, explorers, pilgrims and naturalists Muslim invaders introduced

in India cherries and grapes. Portuguese introduced maize, ground nut, chillies, potato, sweet

potato, guava, pine apple, papaya and cashew nut. East India Company brought tea. Later

Botanic gardens played a major role in plant Introduction

A centralized plant introduction agency was initiated in 1946 at IARI, New Delhi. During

1976 National Bureau of Plant Genetic Resources (NBPGR) was started. The bureau is

responsible for introduction and maintenance of germplasm of agricultural and horticultural

plants. Similarly Forest Research Institute, Dehradun has a plant introduction organization,

which looks after introduction, maintenance and testing of germplasm of forest trees. Besides

NBPGR the Central Research Institutes of various crops also maintain working germplasm. All

the introductions in India must be routed through NBPGR, New Delhi. The bureau functions as

the central agency for export and introduction of germplasm.

At International level International Board of Plant Genetic Resources (IBPGR) with head

quarters at Rome, Italy is responsible for plant introduction between countries.

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Procedure for plant Introduction

The scientist / University will submit the requirement to NBPGR. If the introduction is to

be from other countries, NBPGR will address IBPGR for effecting supply. The IBPGR will

assign collect the material from the source and quarantine them, pack them issue phytosanitary

certificate suitably based on the material and send it to NBPGR. The NBPGR will assign number

for the material, keep part of the seed for germplasm and send the rest to the scientist.

There are certain restrictions in plant introduction. Nendran banana from Tamil Nadu

should be not be sent out of state because of bunchy top disease. Similarly we cannot import

Cocoa from Africa, Ceylon, West Indies, Sugarcane from Australia, Sunflower from Argentina.

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Functions of NBPGR

1. Introduction maintenance and distribution of germplasm

2. Provide information about the germplasm through regular publications.

3. Conduct training courses to the scientist with regard to introduction and maintenance

of germplasm.

4. Conduct exploratory surveys for the collection of germplasm.

5. To set up Natural gene sanctuaries.

Merits of plant introduction.

1. It provides new crop varieties, which are high yielding and can be used directly

2. It provides new plant species.

3. Provides parent materials for genetic improvement of economic crops.

4. Enriching the existing germplasm and increasing the variability.

5. Introduction may protect certain plant species in to newer area will save them from diseases.

E.g. Coffee and Rubber.

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Demerits

1. Introduction of new weed unknowingly.E.g. Argemone mexicana, Eichornia and

Parthenium

2. Introduction of new diseases: Late blight of potato from Europe and Bunchy top of banana

from Sri Lanka

3. New pests: Potato tuber moth came from Italy

4. Ornamentals becoming weeds: Lantana camara

5. Introduction may cause ecological imbalance E.g.Eucalyptus.

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Acclimatization

When superior cultivars from neighbouring or distant regions are introduced in a new area, they

generally fail initially to produce a phenotypic expression similar to that in their place of origin.

But later on they pickup and give optimal phenotypic performance, in other words they become

acclimatized to the new ecological sphere. Thus acclimatization is the ability of crop variety to

become adapted to new climatic and edaphic conditions.

The process of acclimatization follows an increase in the frequency of those genotypes

that are better adapted to the new environment.

The success of acclimatization depends upon two factors

i) Place effect

ii) Selection of new genotypes.

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Selection, Mass selection, pure line selection and Johannson’s pure line theory, genetic

basis.

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Selection in Self-Pollinated Crops

To get successful results by selection there are two pre-requisites.

a) Variation must be present in the population.

b) The variation must be heritable.

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History of selection

Selection was practiced by farmers from ancient times. During 16 [th] century Van Mons in

Belgium, Andrew knight in England and Cooper in USA practiced selection in crop plants and

released many varieties.

Le coutier, a farmer of island of New Jersey published his results on selection in wheat in

the year 1843. He concluded that progenies from single plants were more uniform. During the

same period Patrick Shireff, a scotsman practiced selection in wheat and oats and developed

some valuable varieties.During 1857 Hallet in England practiced single plant selection in wheat,

oats and barley and developed several commercial varieties.

About this time Vilmorin proposed individual plant selection based on progeny testing.

This method successfully improved the sugar content in sugar beet. His method was called as

vilmorin isolation principle. He emphasized that the real value of a plant can be known only by

studying the progeny produced by it. This method was successful in sugar beet but not in wheat.

This shows the in-effectiveness of selection in cross pollinated crops. Today progeny test is the

basic step in every breeding method.

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Pureline theory

A pure line is the progeny of a single self fertilized homozygous plant. The concept of

pureline was proposed by Johannsen on the basis of his studies with beans (Phaseolus vulgaris)

variety called Princess. He obtained the seeds from the market and observed that the lot consisted

of a mixture of larger as well as smaller size seeds.

Thus there was variation in seed size. Johannsen selected seeds of different sizes and grown them

individually.

Progenies of larger seeds produced larger seeds and progenies from smaller seeds

produced small seeds only. This clearly showed that there is variation in seed size in the

commercial lot and it has a genetic basis. He studied nineteen lines al together. He concluded

that the market lot of the beans is a mixture of purelines.

He also concluded whatever variation observed with in a pureline is due to environment

only. Confirmatory evidence was obtained in three ways. In line 13 which is having 450 mg seed

wt he divided the seeds on weight basis. He divided the line into seeds having 200, 300, 400 and

500 mg weights and studied the progenies. Ultimately he got lines having weight ranging from

458 to 475. Thus the variation observed is purely due to environment.

The second evidence was that selection with in a pureline is ineffective. From a pureline

having 840 mg selection was made for large as well as small seeds. After six generations of

selection the line for large seed as well as for small seed gave progenies having 680-690 mg.

Thus it was proved that selection within a pureline is ineffective.

In third evidence when parent - offspring regression was worked in line thirteen. It

worked to zero indicating that variation observed is non heritable and it is due to environment

only.

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Origin of variation in pure lines

1. Mechanical mixtures.

2. Natural hybridization.

3. Chromosomal aberrations.

4. Natural mutation or spontaneous mutation.

5. Environmental factors.

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Effect of self-pollination on genotype

Self-pollination increases homozygosity with a corresponding decrease in heterozygosity.

For example an individual heterozygous for a single gene Aa is self pollinated in successive

generations, every generation of selfing will reduce the frequency of heterozygote Aa to 50

percent of that in the previous generation. There is a corresponding increase in homozygotes AA

and aa. As a result, after 10 generations of selfing virtually all the plant in the population will be

homozygous AA and aa.

No. of generations of selfing	Frequency (%)	Col3	Col4	Frequency (%)	Col6
No. of generations of selfing	AA	Aa	aa	Homozygote	Heterozygote
0	0	100	0	0	100
1	25	50	25	50	50
2	25 + 12.5	25	25 + 12.5	75	25

This can be calculated by the formulae

[2 [m] - 1) / 2 [m] ]" where m = No. of generations of self-pollination and

n = No. of genes segregating.

When number of genes are segregating together, each gene would become homozygous

at the same rate as Aa. Thus the number of genes segregating does not affect the percentage of

homozygosity. Similarly linkage between genes does not affect the percentage of homozygosity

in the population.

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Genetic advance under selection

Normally selection is practiced based on the phenotype of the individual plant. The

phenotype in turn is the result of joint action of genotype and environment i.e.,

VP=Vg +VE Where P= phenotype; G = genotype; E = Environment

The genetic advance is calculated by the following formula.

Genetic advance (GS) = (K) (H) (SD P) or GS = (K) (VP) [ ½] (Vg / Vp),

Where GS is the genetic advance under selection, K is the selection differential, SD P is

the phenotypic standard deviation of base population and H is the heritability of the character

under selection. The estimates of GS have the same unit as that of the mean.

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Pureline Selection

A large number of plants are selected from a self pollinated crop. The selected plants are

harvested individually. The selected individual plants are grown in individual rows and evaluated

and best progeny is selected, yield tested and released as a variety.

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Characteristics of purelines

1. All plants within a pure line have the same genotype.

2. The variation with in a pureline is environmental and nonheritable.

3. Purelines become genetically variable with time due to natural hybridization, mutation

and mechanical mixtures.

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General steps for making a pureline selection

First Season: From the base population select best looking plants having the desirable

characters. Harvest them on single plant basis.

Second Season: The selected single plants are grown in progeny rows and estimate the

performance. Reject unwanted progenies.

Third Season: Repeat the process of second season.

Fourth Season: Grow the selected single plants in replicated preliminary yield trial along with

suitable check or controI variety.

Fifth Season: Conduct regular comparative yield trial along with check variety and select the

best culture.

Sixth Season: Conduct multilocation trial in different research stations along with local check.

Seventh Season: Conduct Adaptive Research Trial in farmer's field. Fix the best yielder and

release it as a variety thro' Variety Release committee.

Advantage of pureline selection.

1. Achieves maximum possible improvement over the original variety.

2. Extremely uniform in appearance.

3. Because of the uniformity, a variety is easily identified and seed certification is easy.

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Disadvantages

1. It does not have wide adaptability because improvement is made only in the local variety.

2. Time required for developing a variety is more when compared to mass selection.

3. Depending on the genetic variability present in the base population only the improvement

is made. If there is no genetic variability improvement cannot be made.

4. Breeder has to spend more time compared to mass selection.

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Mass Selection

Here a large number of plants having similar phenotype are selected and their seeds are

mixed together to constitute a new variety. Thus the population obtained-from selected plants

will be more uniform than the original population. However they are genotypically different.

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Steps

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First season

From the base population select phenotypically similar plants, which may be 200 2000.

Harvest the selected plants as a bulk.

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Second season

The bulk seed is divided into smaller lots and grown in preliminary yield trial along with

control variety. Dissimilar phenotypes are rejected. Higher yielding plots are selected.

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Third to Sixth Season

With the selected lots conduct yield trials along with appropriate check or control. Select

the best one and release it as a variety.

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Merits of Mass Selection

1. Varieties developed will be having more adaptability since each plant is genotypicaly

not similar. They have buffering action against abnormal environment.

2. Time taken for release of a variety is less.

3. The genetic variability present in the original population is maintained.

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Demerits

1. Compared to pure line variety they may not be uniform.

2. In the absence of progeny test we are not sure whether the superiority of selected plant is due

to environment or genotype.

3. May not be as uniform as that of a pureline variety and certification is difficult.

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Comparison between pure line and mass selections

Col1	Pureline selection	Mass selection
1.	The new variety is a pureline	The new variety is a mixture of purelines.
2.	The new variety is highly uniform. In fact, the variation within a pureline variety is purely environmental.	The variety has genetic variation of quantitative characters, although it is relatively uniform in general appearance
3.	The selected plants are subjected to progeny test	Progeny test is generally not carried out
4.	The variety is generally the best pureline present in the original population. The pure line selection brings about the greatest improvement over the original variety	The variety is inferior to the best pureline because most of the purelines included in it will be inferior to the best pure line
5.	Generally, a pure line variety is expected to have narrower adaptation and lower stability in performance than a mixture of pure lines	Usually the variety has a wider adaptation and greater stability than a pureline variety
6.	The plants are selected for the desirability. It is not necessary they should have a similar phenotype	The selected plants have to be similar in phenotype since their seeds are mixed to make up the new variety.
7.	It is more demanding because careful progeny tests and yield trials have to be conducted.	If a large number of plants are selected, expensive yield trials are not necessary. Thus it is less demanding on the breeder.

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III. Hybridization and Selection Methods (Self-Pollinated Crops)

Hybridization creates new genetic combinations by crossing two parents. The segregating hybrid populations are then handled by different methods — each differing in how and when selection is applied.

A. Pedigree Method

The pedigree method involves individual plant selection in every segregating generation from F₂ onwards, with detailed pedigree records maintained for each selected line.

Steps:

Season	Activity
F₁ (Year 1)	Make cross between parents P₁ × P₂; raise F₁
F₂ (Year 2)	Grow large F₂ population (~3000–5000 plants); select best individual plants for target traits
F₃ (Year 3)	Grow progeny rows from each F₂ plant; select best plants within best rows
F₄ (Year 4)	Grow F₄ families; eliminate inferior families; select within promising families
F₅ (Year 5)	Select best lines; begin preliminary yield trials
F₆–F₇	Multilocation yield trials; compare with check variety
F₈ onward	Release as improved variety

Merits of Pedigree Method:

1. Breeder maintains full ancestry record (pedigree) — easy to trace origin of each line.
2. Selection starts from F₂ — early removal of undesirable lines saves resources.
3. Best suited for traits with high heritability (disease resistance, plant height, seed colour).
4. Allows exploitation of additive gene action.
5. Breeder can observe performance of each line over generations.

Demerits of Pedigree Method:

1. Very labour-intensive — large number of progenies must be maintained with records.
2. Not suitable for traits with low heritability (yield, protein content) because early selection is unreliable.
3. Linkage drag — desirable and undesirable genes linked together may be difficult to separate.
4. Large land and resource requirements in early generations.

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B. Bulk Method (Bulk Population Method)

In the bulk method, the entire segregating population from F₂ to F₄ or F₅ is grown as a bulk without individual plant selection. Natural selection operates during this period, and artificial selection is delayed until high homozygosity is achieved.

Steps:

Season	Activity
F₁	Cross P₁ × P₂; raise F₁
F₂ to F₄/F₅	Grow as bulk (no individual selection); natural selection eliminates weak genotypes
F₅/F₆	Harvest individual plants; grow in progeny rows
F₆/F₇	Select superior lines; preliminary yield trials
F₇ onward	Multilocation trials; variety release

Key concept: Natural selection in bulk favours adapted genotypes, so survivors are already partially selected by the environment.

Merits of Bulk Method:

1. Simple and inexpensive — no need to maintain pedigree records in early generations.
2. Natural selection improves adaptation of surviving genotypes.
3. Less labour in early generations — suitable for large-scale breeding programmes.
4. Maintains wide genetic base until selection generation.

Demerits of Bulk Method:

1. Natural selection may eliminate rare but valuable genotypes early.
2. Selection starts late — takes longer to develop a variety than pedigree method.
3. Breeder has no control over which genotypes survive natural selection.
4. Difficult for traits that are not under natural selection pressure.

Comparison — Pedigree vs Bulk Method:

Feature	Pedigree Method	Bulk Method
Selection start	F₂	F₅/F₆
Record keeping	Elaborate pedigree records	No records in early generations
Labour	High	Low
Natural selection role	Minimal	Major
Cost	High	Low
Best for	High heritability traits	Traits under natural selection

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C. Single Seed Descent Method (SSD)

In SSD, one seed per plant from each generation is taken and advanced to the next generation without selection. This rapidly attains homozygosity with the smallest land area.

Steps:

• F₂: Grow ~1000 plants → harvest 1 seed per plant → plant next season
• F₃ to F₅: Repeat — one seed per plant advanced each generation
• F₅/F₆: Plants are ~97% homozygous → now grow progeny rows and apply selection
• F₆ onward: Yield trials and variety release

Advantage of SSD: Can be done in greenhouse/off-season nurseries — completes 2–3 generations per year. Reduces time by 3–4 years compared to pedigree method.

Merits of SSD:

1. Fastest route to homozygosity (2–3 generations/year possible).
2. Every F₂ plant represented in final population — maximum genetic diversity preserved.
3. No selection bias in early generations — breeder can't inadvertently discard valuable alleles.
4. Least land required in early generations.

Demerits of SSD:

1. No natural selection in early generations — unfit genotypes also advanced.
2. Selection applied only at end — high population sizes needed at selection stage.
3. Bottleneck effect — if a plant dies before producing seed, that entire lineage is lost.

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D. Modified Bulk Method

A modification where mild selection is practised within the bulk population — clearly inferior plants are removed while retaining the bulk approach. This combines advantages of both pedigree and bulk methods.

• Applied in F₂/F₃ for obvious undesirables (diseased, off-type plants).
• From F₄/F₅, individual plant selection begins.
• Reduces the size of unwanted genotypes without the full record-keeping of the pedigree method.

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E. Mass-Pedigree Method

The population is maintained as a bulk during unfavourable seasons (drought, disease pressure) and individual selection is practised during favourable seasons.

• Combines bulk handling (saves resources in bad years) with pedigree selection (maximises gain in good years).
• Particularly useful in regions with variable rainfall or biotic stress.

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IV. Methods for Cross-Pollinated Crops

Cross-pollinated crops (maize, bajra, jowar, sunflower, sugarcane) are naturally heterozygous. Selection objectives and methods differ from self-pollinated crops.

A. Mass Selection in Cross-Pollinated Crops

Similar to mass selection in self-pollinated crops — select phenotypically superior plants and bulk their seeds. However, because pollination is random, progenies contain half the genes from unselected pollen donors.

• Progress per cycle is slower than in self-pollinated crops.
• Effective for simply inherited and high heritability traits.
• Still used for improving local populations and open-pollinated varieties.

Improvement: Controlled pollination (detasselling in maize) removes unselected pollen → better genetic gain.

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B. Recurrent Selection

Recurrent selection is a cyclic breeding method designed to gradually increase the frequency of desirable alleles in a population while maintaining genetic diversity.

Basic cycle:

1. Evaluation — grow progenies and measure performance
2. Selection — identify superior genotypes
3. Intercrossing — cross selected plants among themselves to create new base population
4. Repeat the cycle

Types of Recurrent Selection:

Type	Objective	How crosses are made
Simple Recurrent Selection	Improve general combining ability	Selected plants intercrossed
Recurrent Selection for GCA	Improve performance in crosses (GCA)	Testcross with inbred tester
Recurrent Selection for SCA	Improve specific cross combinations (SCA)	Testcross with specific tester
Reciprocal Recurrent Selection (RRS)	Improve both GCA and SCA simultaneously	Two populations crossed reciprocally

Merits:

1. Maintains genetic diversity — avoids fixation unlike selfing methods.
2. Can be repeated indefinitely — no ceiling on improvement.
3. Accumulates favourable alleles gradually but reliably.
4. Suitable for both qualitative and quantitative traits.

Demerits:

1. Time-consuming — each cycle takes 2–3 years.
2. Requires large populations and crossing facilities.

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C. Hybrid Breeding in Cross-Pollinated Crops

Hybrids (F₁ hybrids) exploit heterosis (hybrid vigour) — F₁ plants outperform both parents in yield, vigour, and uniformity.

Steps in hybrid breeding:

1. Develop inbred lines by repeated selfing (6–8 generations) until homozygous.
2. Evaluate inbreds in testcrosses to identify high-combining lines.
3. Produce hybrid seed by crossing best inbred lines.
4. Deploy commercial hybrids — farmers buy new seed each season.

Types of hybrids:

Type	Cross	Example
Single cross (SC)	A × B	High yield, uniform; expensive seed
Double cross (DC)	(A×B) × (C×D)	Lower yield than SC but cheaper seed
Three-way cross (TWC)	(A×B) × C	Intermediate
Top cross	Inbred × OP variety	Easy to produce

Male sterility (cytoplasmic male sterility, CMS) is used to eliminate hand-emasculation — reduces hybrid seed production cost significantly.

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V. Mutation Breeding

Mutation breeding induces artificial mutations using physical or chemical mutagens to generate new genetic variability beyond what exists in the germplasm.

Mutagens used:

Type	Examples
Physical	X-rays, Gamma rays (Cobalt-60), UV light, Neutrons
Chemical	EMS (ethyl methane sulphonate), NMU, DES, Colchicine

Procedure:

1. Treat seeds/pollen/vegetative parts with mutagen at optimum dose.
2. Grow M₁ generation (treated plants) — mostly chimeric, do not select here.
3. Self-pollinate M₁ to get M₂ — mutations become visible; select desired mutants.
4. Continue selection in M₃, M₄ until stable lines obtained.
5. Compare in yield trials and release as variety.

Key Examples:

• Sharbati Sonora wheat — semi-dwarf, amber-coloured mutant from Sonora 64 (gamma rays).
• Jagannath rice — early-duration mutant from T-141 variety.
• NDB-58 (Bhat) — blackgram mutant with bold seeds.
• Parbhani Kranti bhindi — yellow vein mosaic resistant mutant.

Merits:

1. Creates new variability not present in existing germplasm.
2. Can improve a single character without altering the entire genotype.
3. Useful for vegetatively propagated crops where sexual hybridization is difficult.

Demerits:

1. Most mutations are recessive and deleterious — useful mutations rare (1 in 10,000).
2. Requires radiation facilities and trained personnel.
3. Cannot predict the nature of mutation — largely random.
4. Linkage of desirable mutation with undesirable genes is possible.

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Master Comparison Table: All Breeding Methods

Method	Crop Type	Genetic Base	Fixation Time	Key Advantage	Key Limitation
Pure Line Selection	Self-pollinated	Narrow (single homozygous line)	7–8 seasons	Maximum uniformity	No new variation created
Mass Selection	Both	Broader (mixture of lines)	5–6 seasons	Wide adaptability, simple	No progeny test; slower improvement
Pedigree Method	Self-pollinated	Intermediate	8–10 seasons	Full pedigree record; early selection	Labour-intensive; needs high heritability
Bulk Method	Self-pollinated	Broad	10–12 seasons	Low cost; natural selection aids	No control; may lose rare alleles
Single Seed Descent	Self-pollinated	Broad	6–8 seasons (fast)	Fastest homozygosity; off-season possible	No selection benefit early
Backcross Method	Both	Narrow (recurrent parent)	10–14 seasons	Transfers single character precisely	Cannot exceed recurrent parent
Recurrent Selection	Cross-pollinated	Broad	Cyclic (2–3 yr/cycle)	Maintains diversity; indefinitely improvable	Slow per cycle
Hybrid Breeding	Cross-pollinated	F₁ heterozygous	N/A	Maximum heterosis; uniform	Farmer cannot save seed
Mutation Breeding	Both	Variable	6–8 M-generations	New alleles; useful in vegetative crops	Mostly deleterious; random
Polyploidy Breeding	Both	Doubled genome	Variable	New species; seedless fruits	Sterility issues; complex

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Quick Revision: Key Distinctions

Which method for which situation?

• Transfer one gene (disease resistance) into proven variety → Backcross Method
• Improve multiple traits in self-pollinated crop from a cross → Pedigree or Bulk Method
• Need fastest route to homozygosity → SSD (Single Seed Descent)
• Improve cross-pollinated population gradually → Recurrent Selection
• Maximum yield advantage in commercial crop → Hybrid Breeding (F₁ hybrids)
• Create entirely new variation → Mutation Breeding
• Improve local variety directly without crossing → Pure Line Selection

Exam tip — Number of backcrosses: 6 backcrosses are generally sufficient to recover ~99% of recurrent parent genotype ([(2ⁿ–1)/2ⁿ] where n = number of backcrosses).

Exam tip — SSD vs Bulk: Both grow population for several generations without selection, BUT SSD takes exactly 1 seed per plant (preserves all lineages); Bulk harvests all seeds together (loses lineages by drift).

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Summary Cheat Sheet

Quick Recall Points

• This lesson focuses on key plant breeding concepts, terminology, and exam-relevant applications.
• Review major definitions, classifications, and method-wise distinctions from the sections above.
• Revise tables and examples from this lesson for fast pre-exam recall.

Exam Traps

• Do not confuse similarly named breeding methods without checking their core selection logic.
• Pay attention to crop-specific examples because the same principle can behave differently by species.

References

1 source • [1]

[1]

Standard Plant Breeding Class Notes (GPBR211)

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