DIALLEL MATING DESIGN

 

• The diallel mating design generally estimates the variation of quantitative characters in the genetic components like assessment of plant seed quality.
• The estimation is also performed to deduce the combining ability of the different inbred lines which participate in the different crosses taken into consideration.
•  Selection of parental materials and good mating designs in conventional plant breeding are the keys to the successful plant breeding programme.

Types of Diallel Mating Design

The diallel mating design methods can be classified as follows (Griffing 1956).

1.Partial Diallel Design – This is a type of diallel design where a portion of required cross is made. This means in this study design each parent is not mated with every parent in the group leading incomplete or partial genetic cross.

2.Systematic or Progressive Mating Scheme – In this design the crosses which are made, they generally fall in particular diagonals. The diagonals are chosen in such a way that no one parent is interfered in more than few crosses.

3.Disconnected Diallel Scheme – This pattern of design is characterized by the parents who are categorized into tiny groups and diallel or half diallel matings are done within each individual group.

Methodologies for Studying DD:

Griffing (1956) and his coworkers have analyzed the DD elaborately using different models. The mating ability of a particular species is initially portrayed in a tabular form then combining abilities are identified accordingly.

Two types of combining abilities are present:

1.General Combining Ability (GCA)

The ability of the inbred line is the mean performance of the hybrids that this line reproduces with other lines chosen from a random mating population. It is estimated form half-sib families.

 

2.Specific Combining Ability (SCA)

This refers to a pair of inbred lines which are involved in a cross. In this cases certain combinations might do relatively better or inferior than would be predicted on the basis of GCA effects on two lines involved in the study. It is generally deviation of a particular cross from the expectation on the basis of average GCA effects of the two lines involved. It is equivalent to an interaction result of a factorial experiment

DIALLEL ANALYSIS:

According to Griffing (1956) there are four different methods for diallel design based on whether the parents, their reciprocal F1 crosses, or both, are included in the evaluation with the F1 crosses:

Method I or Full Diallel Design: The method I or full diallel design consisted by parents, one set of F1’s and reciprocal F1’s. The system gives n² genotypes (Griffing 1956).

Method II: This method encompasses parents and one set of F1’s without reciprocals F1’s. This design gives n(n + 1)/2 genotypes.

Method III: Here, one set of F1’s and the reciprocals are investigated. This design provides the equation a = n(n −1) different number of genotypes.

Method IV: Here, it only includes F1 crosses. This design provides the equation a = n(n − 1)/2 different number of genotypes.

 

FULL DIALLEL

Full diallel in which parents and reciprocal crosses are involved along with F₁ 

HALF DIALLEL

Half diallel with parent and without reciprocal crosses

 MODELS OF COMBINING ABILITY ANALYSIS

1.Fixed Effect Model

This is also known as model I. It is a method of diallel analysis which is used with diallel set of crosses made among fixed sample of inbred lines. In a fixed effect model the experimental material includes a set of fixed genotypes, say a set of inbreds or varieties. Such set of genotypes is considered as a population and inferences are drawn about individual line/variety.

2. Random Effect Model

It is a method of diallel analysis which is used with diallel set of crosses made among
random samples of individuals from random mating population. In the random effect model, we deal with random sample of a random mating population. In this case, inferences can not be drawn about individual line but about, the parent population as a whole.

The procedure for the analysis of variance remains the same in both the models, but the
expectations of mean squares due to various items are different and, therefore, the interpretation of results also differs.

 

Applications

The DD study estimates the genetic makeup of variation of a quantitative character.

q  It also estimates the combining efficacies of different inbred lines involved in the cross.

q  A random model involves parents that are random members of a random mating population.

q  A random model is useful for estimating GCA and SCA variances. These effects only apply to the set of parents in the diallel.

It is also widely used for developing breeding populations for recurrent selection (Acquaah 2012). In addition, Johnson and King (1998) reported that diallel mating designs are deployed to provide the maximum opportunity to manage coancestry in breeding population and maximize selection differential