Mating Designs (in forest trees)–their importance, types and relative significance in genetic testing programmes.

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BY:SATYABRATA NAYAK2015-17-013

What is mating design?It refers to a system of crossing, which is used to develop progenies of certain kind that serve to predict the genetic worthiness of their parents.

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The methods by which trees are combined to produce progeny is called as mating design.

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Progeny testing

Estimation of variance components

Determination of GCA and SCA

Creation of base population

Determination of narrow sense heritability

Estimation of genetic gains

Objectives of mating design:

Types of mating design

Incomplete pedigree designs

Only one parent (usually the mother tree) is known

Complete pedigree design

Both the parents are known

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A. Incomplete pedigree design:

1. Open pollinated mating

2. Pollen mix design

B. Complete pedigree design:

1. Nested design2. Factorial design3. Single- pair mating4. Full diallel mating

design5. Half diallel design6. Partial diallel design

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A.1. Open pollinated mating

• Trees are allowed to mate random through open pollination

• Then seeds are collected and kept separate by family.

Collection of seed is generally followed by two methods:o From Plus trees in natural stands or plantation o From seed orchards

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Advantages:1. GCA can be estimated 2. Helps in rogueing of genetically inferior trees3. Advanced generation selection can be made4. Provides estimates of additive gene variances and heritability

values5. Easiest and least expensive6. Used to quickly test selected trees

Disadvantages:1. SCA cant be estimated2. Limited utility for future generation3. Possibility of selfing4. Inbreeding depression5. Lack of complete pedigree

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A.2. Pollen mix design(Also called polycross design and sometimes topcross)

• Some trees are selected as male parents and their pollen (equal

quantities) are collected and mixed.

• The mixture is then applied to female parents

• Generally a considerable number of pollens are included in the

mix to insure that female parents are pollinated by a

representative sample of other parents

• No. of male parents should not less than 10

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Advantages:1. GCA can be estimated2. Additive gene variance3. Heritability4. Breeding value5. Less expensive than other mating designs except

open pollinated mating design

Disadvantages1. SCA can not be estimated2. Breeding value may be biased3. Advance generation selection is difficult

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B. Complete pedigree design

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B.1. Nested designAlso called hierarchial or North Carolina State Design 1

• Group of parents of one sex (male/female) are mated with to members of other sex.

• Progeny produced is composed of both full-sib that have both parents in common and half sibs that have only one parent is common

Advantages:1. It allows to estimate both additive and non-additive variances

and heritability

Disadvantages 1. GCA can be obtained only for members of rarer sex2. Small no of unrelated family

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B.2. Factorial designIt is a modification of nested designAlso known as Tester or Line ˣ tester design and also North Carolina State Design 2• Here members of one sex are crossed in all combinations with

several members of the other sex• Most commonly in forestry 4 to 6 parents designated as testers

are crossed with all other parents in the population .

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Advantages:1. Very useful in progeny testing programme2. Allows a reasonable estimation of variance components and

heritabilities3. GCA and SCA can be estimated4. Additive and non additive variances

Disadvantages 1. The number of parents that can be selected for the subsequent generation

will be limited to the number of testers 2. Small no of unrelated families

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B.2.b. Disconnected factorial designModification of factorial design

Breeding population is divided into several sets of parents and a factorial mating design employed within each set

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Advantages:1. Maximize the no. of unrelated families2. Good estimation of GCA and SCA3. Good estimation of realized and expected gains that arise

from additive and non additive variation4. Estimation of variance components and heritability

Disadvantages 1. Less efficient than the tester design for progeny testing2. GCA is biased

B.3. Single pair mating

Each parent is mated to one other member of the population only once

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Advantages:1. Creates the maximum no. of unrelated families in each

generation with a minimum no. of crosses.2. Easy to carry out3. SCA is estimated4. Heritability and variance components are estimated 5. Complete avoidance of inbreeding

Disadvantages 1. Not suitable for roguing seed orchard2. GCA and breeding value cant be estimated3. Even number of trees required all time

B.4. Full Diallel mating design• Each parent crosses to all

others in every combination which involves direct crosses, reciprocal crosses, and all selfed plants.

• It is the most comprehensive mating design available

• No of crosses = n², where n= no. of parents

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Advantages:1. Estimation of GCA, SCA2. Maximum number of unrelated families3. It is good to estimate all genetic parameters

Disadvantages :1. Very cumbersome 2. No of crosses is very large3. Time consuming4. Costlier than all others5. Rarely used in progeny testing

B.5. Half diallel design• Modification of complete diallel

design• Each parent is mated to every

other parent once as a male parent only

• So there is no reciprocal crosses made.

• If there is no need of selfed crosses, such crosses are also omitted

• So no of crosses will be n(n-1)/2, where n = no. of parents

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Advantages:1. Good estimation of GCA ,SCA and genetic

parameters2. Less expensive than full/ complete diallel

mating

Disadvantages 1. Not efficient as full diallel design2. The no of crosses still large 3. Also rarely used

B.6. Partial diallel design• Another modification of diallel design

• Only a portion of required crosses are made, that is each parent is not mated to every parent in the orchard.

Partial diallel design again classified into ;

systematic or progressive mating scheme

disconnected diallel scheme

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B.6.a. Systematic or progressive mating scheme

• In this design crosses are made that fall in particular diagonals.

• Diagonals are chosen so that no one parent is involved in more than few crosses

Advantages:1. Maximum no of unrelated crosses 2. Estimation of GCA for each parent3. Estimation of additive and non

additive variances4. Estimation of SCA for a part of

possible combinations

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B.6.b. Disconnected diallel scheme• In this design parents are

divided into small groups, and diallel or half diallel mating are done within each group

Advantages:1. This design maintains most of

advantages of more complete diallel but greatly reduces the number of crosses

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Mating design Estimation of GCA

Estimation of SCA Estimation of genetic gain Cost

Open-pollinated Fair No Gives information on realized and expected gains Very low

Polycross design Very good Not possible Realized and expected gains calculated from additive variance Low

Nested design Good for rarer sets Not good -do- Somewhat less

Factorial design Good GoodRealized and expected gains from both additive and non additive variances

Fair

Disconnected factorial Good Good -do- Fair

Single pair Not possible Good Good estimation of realized gains Very low

Full diallel Excellent ExcellentGood estimation of realized and expected gains from additive and non-additive variances

Very high

Half diallel Excellent Excellent -do- Very high

Partial diallel Good Good -do- Fair

Disconnected diallel Good Good -do- fair

Comparative efficiency of mating designs:

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The genetic composition of the population can be changed through selection and mating design

Mating design helps develop progenies and provide information about the nature of gene action

Mating design are helpful in evaluating progenies and selection of parents from the performance based on GCA, SCA and nature of gene action.

Mating design also help in creating variability and thereby selection and advancement of subsequent advanced generation

SUMMARY: