GENETIC STUDIES ON RECIPROCAL SELECTION FOR COMBINING ABILITY TO IMPROVE HYBRID PERFORMANCE IN COTTON (Gossypium hirsutum L.)
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Date
2007-08-30
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University of Agricultural Sciences GKVK, Banglore
Abstract
Hybrid breeding programmes in eross pollinated erops like maize are
supported by various schemes for improving combining ability by handling
combining ability as a trait. By utilizing such scheme genetically diverse lines
are developed, which when used, give rise to superior hybrid combinations,
such method can be employed in cotton. The experimental material of this study
was constituted by a set of four hirsutum varietal (parental) lines namely RAH 10
(A), RAH 100 (B), RAH20 (C) and RAH200 (D) forming two diverse single
(RAHH102 (A X B) and RAHH136 (C x D)) crosses which are found to be veiy
diverse from each other based on predicted double eross performance.
Twenty six random F4 lines derived from these two single crosses were
selected for use in assessing the variability for combining ability. These lines are
crossed with three common testers viz., AACHH1065 (T3), 435308 (T4) and ZCH-
21045 (T5). Another two different testers were used as uncommon/reciprocal
testers where RAHH136 (Ti) hybrid serves as a tester for evaluating F4 lines of
RAHH102 lines and vice versa te., RAHH102 (T2) hybrid serves as a tester for
testing combining ability of F4 lines of RAHH136 lines.
The magnitude of variability for combining ability was assessed in terms
of range, variance, coeflieient of variance and mean seed cotton yield of these
derived Fis (26 dFis per tester) in comparison with straight crosses (crosses of
parental lines A, B, C and D with tester concerned) and commercial check. By
comparing dFis with superior straight crosses, the magnitude of transgressive
segregation for combining ability was determined. Efficiency of testers were also
determined based on the mean and variances of the derived Fis. Based on this
435308 (T4) was found to be most efficient in distinguishing the F4 lines of the
both crosses,
A sizeable portion of derived Fis was significantly superior over
commercial check. Among F4 lines R-2 (102) (of RAHH 102) and R-5 (136) (of
RAHH 136) lines showed highest improvement in combining ability for seed
cotton yield and with regard to fibre properties R-1 (136) and R-6 (102) are the
potential combiners. Based on weighted per cent gea method R-11 (102), R-18
(102), 1^21 (136) and R-3 (136) F4 lines were found to be potential combiners
with higher pooled scores. The SCA variance for seed cotton yield- was high
confirming the role of non-additivity including dominance in governing the
expression of seed cotton yield. This also confirms the role of dominant
favourable alleles in influencing the seed cotton yield. The combining ability
status of most productive crosses in this study helped in drawing the inference
about handling the best crosses. Apart from sea, gea effects also contributed to
superiority of these crosses justifying the emphasis on developing these Fis into
commercial hybrids.
In general, the correlation between genetic distances through RAPD
among parents and the heterosis shown by their hybrids was non-signifieant
may be because the molecular markers used to calculate genetic distances are
not linked to the genes controlling seed cotton yield.
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