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Genomics and Applied Biology
27
Table 4 Correlation coefficients of genetic distance (GD) with F
1
performance and heterosis
Traits
Mid parent heterosis
F
1
performance
Heterosis over Mrc6918 check
Heterosis over DCH32 check
Number of bolls per plant
-0.347
-0.181
-0.177
-0.177
Mean boll weight (g)
-0.222
-0.297
-0.290
-0.290
Seed index (g)
0.193
0.170
0.164
0.164
Ginning outturn (%)
0.237*
0.277**
0.279**
0.279**
Lint index (g)
0.227*
0.251*
0.250*
0.250*
Seed cotton yield (kg/ha)
0.226*
0.359**
0.336**
0.362**
Fibre length (mm)
0.210*
0.120
0.120
0.120
Fibre strength (g/t)
-0.179
-0.130
-0.130
-0.130
Fibremicronairvalue(µg/inch)
0.266**
0.241*
0.241*
0.241*
Fibre uniformity ratio %
-0.036
-0.056
-0.056
-0.056
Fibre maturity ratio
0.221*
0.141
0.148
0.148
Fibre elongation %
-0.241
-0.119
-0.118
-0.118
* Significant at P = 0.05 ** Significant at P = 0.01
DNA based molecular markers acted as a versatile tool
to study variability and diversity in different plant
species. The development of DNA based markers
represent an alternative procedure of the identification
of promising parental lines for superior performances
of hybrids. The microsatellite (SSR’s) markers have
been widely used for the estimation of variation
among closely related individuals due to its
multiallelic nature and high polymorphism. Molecular
markers based on polymorphism of DNA are
especially useful for this purpose because they are not
affected by environment (Tatineni et al., 1996;
Saghai-Maroof et al., 1984). Several examples of the
application of molecular markers to estimate genetic
distances have been reported in maize (Smith et al.,
1990) and rice (Zhang et al., 1995). Thus, molecular
markers like SSR’s (microsatellite) could be used for
germplasm classification and clustering to derive
valuable information for heterosis prediction.
Therefore, they were useful for heterosis prediction in
seed cotton yield, lint index, ginning outturn and fiber
micronaire. According to Bernardo (1992) inadequate
genome coverage, random dispersion of molecular
markers (unlinked to QTLs) and different levels of
dominance could be the reason for low correlation
between molecular distance and heterosis and/or F
1
performance. The existence of multiple allelism and
epistasis could also cause the low correlation of GD
and F
1
performance/heterosis.
An assessment of the usefulness of molecular markers
in breeding cotton for yield and fiber quality
improvement may therefore need further consideration.
More molecular markers covering all 26 chromosomes
and at higher densities and molecular markers that are
linked to QTL for agronomic traits and fiber
properties are needed for further studies.
2 Materials and Methods
2.1 Plant materials and field evaluation
During 2010 the twenty eight F
4
lines of (
Gossypium
barbadense
L.) (Table 5) cross (DB 533 × DB 534)
depending on the highest of fiber strength, are
proposed to be crossed with the four common diverse
(Gossypium hirsutum L.) viz., DH 98-27 (T
1
), ZCH8
(T
2
), 178-24 (T
3
) and DH 18-31 (T
4
) selected based on
the earlier study. The crossing programme was taken
up during 2010. The F
4
lines and four common testers
were sown on staggered dates. To obtain derived F
1
s
seed, the flower buds of the proper size from testers
(used as female) were hand emasculated in the
evening between 3.00 to 6.00 pm. The emasculated
flowers were covered by butter paper packets for
avoiding out crossing as well as ensuring their easy
identification at the time of crossing. The emasculated
Genomics and Applied Biology