This document discusses general combining ability (GCA) and specific combining ability (SCA) in plant breeding. GCA is due to additive genetic effects and refers to a genotype's average performance in crosses. SCA is due to non-additive genetic effects and refers to when certain crosses perform better or worse than expected. GCA is estimated using half-sib mating and helps identify best parents for hybridization. SCA is estimated using full-sib mating and helps identify best cross combinations. The document outlines procedures for estimating and utilizing GCA and SCA over multiple generations or seasons in plant breeding programs.

1. Presentation on GCA and SCA

2. Introduction:
 Combining ability in crosses is defined as the
ability of parents to combine amongst each other
during the process of fertilization so that
favourable genes or characters are transmitted to
their progenies.
 Two types of combining ability, general (GCA)
and specific (SCA), have been recognized in
quantitative genetics.
 The concepts of general combining ability (GCA)
and specific combining ability (SCA) were first
introduced by in relation to corn breeding and
have been expanded into animal breeding by
and others

3.  The term GCA is used to designate the average
performance of an inbred line in hybrid combinations
 SCA is used to designate those cases in which
certain combinations do relatively better or worse
than would be expected on the basis of the average
performance of the lines involved.
 According to GCA is due to genes which are largely
additive in their effects and SCA is due to genes with
dominance or epistatic effect .

4. Feature of General Combining
Ability
 It is due to additive genetic variance and additive
x additive gene interaction.
 It denotes combining ability of genotype
esp. inbred with various testers.
 Helps in identification and selection of best
genotype to use it in hybridization, as a parent.
 Estimated by half sib mating
 Have relationship with narrow sense heritability

5. Procedure for estimating and
utilizing General Combining Ability
(GCA):
 1) First Year:
 Superior plants for the character under
improvement are from the base population. The
selected plants are selfed and also crosses
heterozygous tester having broad genetic base.
The selfed seed is kept storage.
 2) Second Year:
 The crossed seed is sown and the combining
ability selected plants is evaluated and plants with
good GCA are identified.

6. Cont..
 3) Third Year:
 The progeny of selected plants with good GCA are
grown from their selfed seed kept in cold storage.
These progenies are inter mated in all possible
combinations and their crossed seed is composited
to form a new source of population for further
selection. This complete original selection cycle.
Many such cycles may be made to obtain desired
results.
 Main features of this method to use for genetic
improvement of quantitative characters in which
selection is made or the basis of test crosses
performance. This method also used for providing
good of population and required three season or year

7. Features of Specific Combining
Ability
 It represents deviation from gca.
 It is due to dominance genetic variance and all
the three types of gene interactions
 Helps into identification and hence selection of
best cross combinations i.e. those with the
desired output.
 When we see that a inbred line combines well in
any cross, it is due to specific combining ability.
 Estimated by full sib mating
 Have relationship with heterosis

8. Procedure for estimating and
utilizing special combining
activity(SCA)
 1) First Year:
 Several plants are selected and selfed. The selected
plant ( male) are also crossed to an tester( female).
 2) Second Year:
 R.Y.T is conducted using test cross progeny. Outstanding
progenies are identified.
 3) Third Year:
 Selfed seed from the progeny are planted in separate
progeny row in a crossing block. All possible inter cross
are made by hand among progeny. Equal amount of
seed is composited, this complete the original selection
cycle

9. Cont.
 4) Fourth Year:
 The combination seed is planted and operation of
1st year repeated.
 5) Fifth Year:
 Second year operation repeated.
 6) Sixth Year:
 Third year operation repeated.