Parental value: Combining ability estimates from Line x tester analysis for yield components in potato genotypes

NEERAJ SHARMA

Combining abilityAbility of a strain to produce superior progeny upon hybridization with other strains

• General combining ability (gca): Average performance of a genotype in a series of cross combination. It is estimated from half-sib family means the crosses which have one parent in common are used for the calculation. gca helps in selection of suitable parents for hybridization.

• Specific combining ability (sca): Deviation in performance of a cross combination from that predicted on the basis of general combining abilities of the parents involved in the cross.

• Crosses have to be made either in diallel or line x tester fashion.

• Combining ability analysis helps in evaluation of inbreds in term of their genetic value, and in the selection of suitable parents for hybridization.

• Combining ability analysis helps in the identification of superior hybrid combinations which may be utilized for commercial exploitation of heterosis.

• Combining ability analysis provides information about the gene action involved in the expression of various traits and helps in deciding the breeding procedure for genetic improvement of such traits.

Line x tester

• The concept of Line x tester was developed by Kempthorne (1957). It is modified form of top cross scheme.

• The genotypes or cultivars to be evaluated are selected from the germplasm. Some of the genotypes are designated as male (testers) and others as female (lines). Each male parent is crossed with each female parent, but male/female parents are not crossed with each other.

• Normally minimum two and maximum 8-10 testers should be used.• Testers should represent broad genetic base, with commercial

adaptation, if possible.

Two methods of planting material for making crosses

• Unpaired planting: each parent is planted only once in crossing block. Population of the male parent is kept always much higher than female parents, because each male is crossed with all the females.

• Paired planting: the parents to be mated are planted adjacent to each other in pairs.

Steps for analysis

1. Analysis of Variance

The first step is to perform analysis of variance and test the significance of differences among the genotypes including crosses and parents. If these differences are found significant, line x tester analysis is done.

Source df SS MS F calculatedReplication r-1 Sr Mr  Mr/Me

Treatment t-1 St Mt Mt/Me

Error (r-1)(t-1)  Se Me  Total  (rt-1)      

2. Line x Tester AnalysisAnova for combining ability

Source df SS MS FReplication r-1 Sr Mr Mr/ Me

Treatment t-1 St Mt Mt/ Me

Parent p-1 Sp Mp Mp/ Me

Crosses c-1 Sc Mc Mc/ Me

P v/s C 1 Sx Mp v/s Mc Mp v/s Mc/ Me

Lines f-1 Sf Mf Mf/ My

Testers m-1 Sm Mm Mm/ My

Lines x Testers

(f-1) (m-1) Sy My My/ Me

Error (r-1)(t-1)   Me

Total  (rt-1)      

3. Estimation of gca and sca effectsFor testing significance of gca and sca

SE (gca for lines)= √(Me/ r x m)

SE (gca for testers)= √(Me /r x f)

SE (sca effects)= √(Me /r)

For calculation of CDgca: SE (gi-gj) line=√(2 Me /r x m)

gca: SE (gi-gj) tester=√(2 Me /r x f)

sca: SE (sij-skl)= =√(2 Me / r)

CD= SE difference x t value

4. Genetic component

σ 2gca/ σ 2sca= 1 (equal proportion)σ 2gca/ σ 2sca greater than 1 (additive)σ 2gca/ σ 2sca less than1( dominance or non-additive)

-If gca variances are higher than sca variances-preponderance of additive gene action and progeny selection will be effective-If sca variances are higher-preponderance of non-additive gene action (dominance and epistasis), heterosis breeding will be effecitve.-If both are equal-both are equally important and reciprocal recurrent selection may be used.

5. Proportional contribution of lines, testers and their interactions to total variance

• Contribution of

lines= SS(l) x 100/SS(Crosses)testers= SS(t) x 100/SS(Crosses)Lines x testers= SS (lxt) x 100/SS(Crosses)