Differences among different method .pdf

M@hbub 1

Comparison among Hybrid, Synthetics and Composite
Sl. No.
1

Basis

Hybrids

Base population

Inbreds

Synthetics

Composite

Inbreds or clone

Varieties or other
heterozygous source.

2

Parents

Usually 2-4 (6

4-10

Two to many

Random, open

Open pollinated

in triple cross)
3

Pollination

Controlled

pollinated
4

General combining

Tested

Tested

Usually not tested

More

Less than hybrid and

Less than hybrid

ability (GCA)
5

Heterosis

composite
6

Seed used

F1

F1 to F4

F1 to F4

7

Seed cost

More

Less than composite

Less than hybrid

and hybrid
8

Seed replacement

Annual

After 3-4 years

After 3-4 years

9

Varietal maintenance

Di cult

Easy

Easy

10

Re-construction

Possible

Possible

Not possible

Differences between Autopolyploid and allopolyploids
Character
1) Chromosome

Autopolyploid

Allopolyploid

Multiple of one genome.

Multiple of two or several genome.

2) External

Resembling a single diploid

Resembling of two or more

morphology

ancestral.

ancestral.

3) Chromosome

Multivalent, frequent

Mostly univalent, multivalent due to

number

pairing
4) Segregation

auto synthesis.
Polysomic

Polysomic to diosomic

i. Watermelon (Citrullus vulgaris)

i. Cultivated wheat (Triticum

pattern in F2
5) Example

ii. Sugarbeets (Beta vulgaris)

aestivum).

ii. Cultivated Tobacco (Nicotiana

tabacum)
Genetics and plant breeding

M@hbub 2

Comparison among clones, purelines and inbreds
Particulars

Clone

1) Mode of

Pureline

Inbred

Cross pollination.

Self pollination

Cross pollination

Asexual

Sexual

Sexual

Heterozygous

Homozygous

Heterozygous

4) Obtained

Asexual

Natural self

Arti cial self pollination or

through

reproduction from

pollination from a

close inbreeding and

a single plant.

single homozygous

Selection for several

plant.

generation.

pollination
2) Nature of
reproduction.
3) Genetic
make-up

5) Maintained

Asexual

Natural self

Arti cial self pollination or

through

reproduction

pollination

close inbreeding.

6) Genotypically

Identical

Identical

Almost identical

7) Used directly

Yes

Yes

No

Plants

Plants

Plants, animal

as a variety
8) Organism
where found.

Distinguish between Biotic & Abiotic Stress
Biotic stress

Abiotic stress

1. Biotic stress include living organism. 1. Abiotic stress include physical factors of
e.g. insect, pest, bacteria, fungi etc.

environment.

e.g.

Temperature,

moisture,

wind, soil salinity and alkalinity etc.
2. The e ect of biotic stress is changeable.

2. The e ect of abiotic stress is stable.

3. The e ect of biotic stress is density

3. Density independent.

dependent.
4. Directly related to stress.

4. Indirectly related to stress.

5. Generally man can control it such as 5. Generally man can not control it. e.g. high
spraying insecticides in case of insect.

temperature beyond the control of stress.

Genetics and plant breeding

M@hbub 3

Comparison between Pedigree and bulk method
Pedigree method

Bulk method

1. Individual plants are selected in F2 and 1.

F2

and

subsequent

generations

are

the subsequent generations and individual maintained as bulks.
plant progenies are grown.
2.

Arti cial

selection,

arti cial

disease

2.

Arti cial

selection,

arti cial

disease

epidemics, etc. are an integral part of the

epiphytotics etc. may be used to assist natural

method.

selection. In certain cases, arti cial selection
may be essential.

3. Natural selection does not play any role in 3.
the method.

Natural

selection

determines

the

composition of populations at the end of the
bulking period.

4. Pedigree records have to be maintained 4. No Pedigree records are maintained.
which

is

often

time

consuming

and

laborious.
5. It generally takes ~12 years to develop a 5. It takes much longer for the development
new variety and to release it for cultivation.

and release of a variety. The bulk population
has to be maintained for more than 10 years
for natural selection to be e ective.

6. It is the most widely used breeding 6. It has been used only to a limited extent.
method.
7. It demands close attention from the

7. It is simple, convenient and inexpensive

breeder from F2 onword as individual plant and does not require much attention from the
selection have to be made and Pedigree

breeder during the period of bulking.

records have to be maintained.
8. The segregating generations are space

8. The bulk populations are generally planted

planted to permit individual plant selection.

at commercial planting rates.

9. The size of population is usually smaller

9. Large population are grown. This and

than that in the case of bulk method.

natural selection expected to increase the
chances

of

segregants.

Genetics and plant breeding

recovery

of

transgressive

M@hbub 4

Comparison between backcross and Pedigree method
Pedigree method

Backcross method

1. F1 and the subsequent generations are

1. F1 and the subsequent generations are

allowed to self pollinate.

backcross to the recurrent parent.

2. The new variety developed by this 2. The new variety is identical with the
method is di erent from the parents in recurrent parent except for the character
agronomic and other characteristics.

under transfer.

3. The new variety has to be extensively 3. Usually extensive testing is not necessary
tested before release.

before release.

4. The method aims at improving yielding 4. The method aims at improving speci c
ability and other characteristics of the

defects of a well adapted, popular variety.

variety.
5. It is useful in improving both qualitative

5. It is useful for the transfer of both

and quantitative characters.

quantitative

and

qualitative

characters

provided they have high heritability.
6. It is not suitable for gene transfer from
related

species

and

for

6. It is the only useful method for gene

producing transfer

substitution of addition lines.

from

related

species

and

for

producing addition and substitution line.

7. Hybridisation is limited to the production 7. Hybridization with the recurrent parent is
of F1 generation.

necessary

for

producing

every

backcross

generation.
8. The F2 and the subsequent generation are

8. The back cross generations are small and

much larger than those in the back cross usually consists of 20-100 plants in each
method.

generation.

9. The procedure is the same for both

9. The procedures for the transfer of dominant

dominant and recessive genes.

and recessive genes are di erent.

Genetics and plant breeding

M@hbub 5

Comparison between pureline and mass selection
Pureline selection

Mass selection

1. The new variety is a pure line.

1. The new variety is a mixture of purelines

2. The new variety is highly uniform. In fact, 2. The variety has genetic variation for
the variation present within a pureline

quantitative characters, although it would be

variety is purely environmental.

relatively uniform in general appearance.

3. The selected plants are subjected to 3. Progeny test is generally not carried out.
progeny test.
4. The variety is generally the best pure line

4. The variety is inferior to the best pure line

present in the original population. The pure

because most of the pure lines included in it

line selection brings about the greatest will be inferior to the best pureline.
improvement over the original variety.
5. Generally, a pureline variety is expected 5. Usually the variety has a wider adaptation
to have a narrower adaptation and lower

and greater stability than a pureline variety.

stability in performance than a mixture of
pure lines.
6.

The

plants

are

selected

for

their

6. The selected plants have to be similar in

desirability. It is not necessary that they phenotype since their seeds are mixed to
should have similar phenotype.

make up the new variety.

7. It is more demanding because careful 7. If a large number of plants are selected,
progeny tests and

eld trials have to be

conducted.

extensive

eld trials are not necessary. Thus,

it is less demanding on the breeder.

8. Generally, 7 to 8 years are required to 8. Generally, 6 to 7 years are required to
develop a new variety.

develop a new variety.

9. Selection within a pureline variety will be

9. Selection within a variety developed

ine ective unless it has become genetically though mass selection will be e ective since it
variable.

has genetic variation.

10. The produces of a pureline variety is 10. The produce is generally not uniform
uniform in quality.

since di erent purelines making up the
variety may di er in the quality of their
grains, etc.

11. The variety is easily identi ed in seed in 11. The variety is relatively di cult to
certi cation programs.

identify seed certi cation programs.

12. Pureline

12. Mass selection is used in both self and

selection is used in self

pollinated and often cross pollinated crops.

cross pollinated crops.

Genetics and plant breeding

M@hbub 6

Comparative study among the four methods of recurrent selection
Item
1. Source

SRC

RS-GCA

RS-SCA

RRS

1

1

1

2

2 years

3 years

3 years

3 years

No tester

Heterozygous

Homozygous

Open population

4.Exploitation

Additive

Additive

Non- additive Both additive and

/ Utilization of

genetic

genetic

genetic

non-additive

genetic

variance

variance

variance

genetic variance

No test

GCA-test

SCA- test

Both GCA and SCA

population
2. Duration/
Selection cycle
3. Types of
tester

variance
5. Type of test

test

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Genetics and plant breeding