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Cotton Genomics and Genetics
18
Among four barbadense lines positive
gca
effects for
seed cotton yield was recorded by DB 533 and DB
534 confiriming the potential of these barbadense
lines in developing productive interspecific hybrids.
Among 23 hirsutum testers, four testers DH 98-27,
ZCH 8, 178-24 and DH 18-31exhibited good positive
values of
gca
effects for seed cotton yield and were
located among top ten testers ranks 2, 8, 1 and 7
respectively when compared to other hirsutum testers.
2.2 Pooled score for
gca
effect
The overall combining ability status of barbadense
lines and hirsutum testes was determined by working
out pooled
gca
score. Three methods namely simple
gca
score, per cent
gca
and weighted
gca
method were
used in arriving at the best general combiner lines.
The overall ranking from these approaches differed
and the weighted
gca
approach helped in preciese
identification of potential combiners.
2.3 Simple pooled
gca
score method
In this approach, significant
gca
effect in desirable
direction is given positive weightage (+1) and
negative weighatage (-1) is given for
gca
effect in
undesirable direction (Arunachalam and Bandopadhyay,
1979). These values are added over different yield
influencing characters to arrive at pooled score of
gca
effects. The inherent disadvantage with this system is
that all the parents with significant
gca
effects in
desirable direction get the same score (positive).
Hence, it is not possible to quantify the magnitude of
difference existing among the genotypes of this group
which get a positive score. Therefore, it is necessary
develop a system of working out pooled scores of
gca
by utilizing the actual
gca
values and ensuring
quantification of every possible difference existing in
gca
effects between only two parents.
2.4 Per cent
gca
method
When the actual
gca
values are added across
characters to arrive at pooled score, problem arises
because of difference in unit of measurement of each
character. Absolute values of
gca
effects may be big
(plant height) or small (boll weight) depending on the
character and if used, the importance of the character
may not be projected correctly. If the raw values of
gca
effects are added across the characters, the
character with higher
per se
effect influence the
pooled scores most as against the character with low
per se gca
values. To overcome this disadvantage, the
raw
gca
values have to be converted into per cent
gca
values.
Thus, by working out per cent
gca
values, the minute
differences in
gca
values are also focussed and the
possible problem arising out of the differences in unit
of measurement, high and lower
per se gca
values
associated with the type of character concerned are
overcome.
2.5 Weighted per cent
gca
method
In this method further improvement is brought about
in arriving at the pooled
gca
scores of the parents. In
per cent
gca
method, the per cent
gca
values are
straight away added across the characters which
means each character including yield and yield
components are all given equal weightage. The
experience of the breeders would suggest sometimes
that, in arriving the pooled score, it is desirable to
attach differential weightages to each of the characters
studied depending upon its economic importance,
contribution to yield
etc.
These weightages can be
multiplied with per cent
gca
values of corresponding
characters and then added to arrive at the pooled
gca
score for each parent. In the present study weightages
for different yield related characters were worked out
by consulting the senior breeder related to cotton
viz.,
Dr. S. S. Patil, Senior Scientist, Agricultural Research
Station, Dharwad and Dr.B.C.Patil, principal scientist
(Plant physiology), ARS, Dharwad Farm.
Based on weighted
gca
method the most potential
combiners were found to be the hirsutum testers DH
13-7, DH 98-27 and DH 18-31. Among the
barbadense lines, the lines DB 534 and DB 533 based
on weighted
gca
method is the most potential parents.
3 Materials and Methods
The main objective of this Line x Tester study was to
determine the combining ability status of the
barbadense and hirsutum lines included in the
heterotic box. These lines were compared with other
barbadense and hirsutum lines. For the pattern of
combining ability and the potentiality of the
interspecific hybrids developed based on them.