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Wheat Information
Service
Number 80: 12 - 19 (1995)
Heterosis
and combining ability estimates in diallel crosses of six cultivars
of spring wheat
A.S.
Larik1, A.R. Mahar2 and H.M.I.
Hafiz3
Department of Plant Breeding and Genetics, Sindh Agriculture
University, Tandojam-70060, Pakistan
Department of Botany, Shah Abdul Latif University, Khairpur,
Pakistan
Department of Botany, Quaid-e-Azam Campus Punjab University,
Lahore-54590 Pakistan
Summary
The present research programme was conducted to study heterosis
and combining ability for yield and its primary components in a 6 x 6
complete diallel cross involving six varieties of spring wheat. These
genetic parameters were studied in F1 generation for eight
quantitative traits in a randomized block design during the year
1990-92. All the traits exhibited considerable level of relative
heterosis (MP) and heterobeltiosis (BP). The extent of heterosis was
appreciably influenced by the hybrid genotype, the direction of the
cross and the trait concerned. Eight F1's displayed
heterotic values more than 60% for yield per plant. The analysis of
combining ability indicated that a large portion of the total genetic
variation for five out of eight traits was associated with genes
which were additive in their effects, while nonadditive gene action
was strong for single plant yield. The estimates of SCA were
significant for four out of eight traits indicating the presence of
epistasis and dominant gene effects in these traits. The parents,
Z.A.77 and T.J.83 were good general combiner for grain yield.
Magnitude of GCA variance was more pronounced than SCA variance for
all the traits. Therefore, selection has been advocated on the basis
of GCA's of hybrids and breeding method should be designed to exploit
both additive and nonadditive gene action.
Introduction
One of the most important developments in plant breeding in
recent years has been the use of heterosis particularly in allogamous
crops (Baloch et a]. 1991; Larik and Hussain 1990), and has also
been observed in autogamous crops (Larik et al. 1992). Heterosis is
the biological phenomenon and may be due to factors such as
heterozygosity, allelic and non- allelic interaction, epistasis,
dominance or overdominance. Breeding for yield includes genetical
manipulation of the yield components which are polygenetically
inherited exhibiting additive and non-additive genetic variation. On
the contrary, combining ability analysis of cultivars is necessary to
exploit the relevant type of gene action for a breeding programme. If
SCA is predominant, it can be used in hybrid breeding programme.
In this context the present study was undertaken to study heterosis
and combining ability in F1 generation of wheat
(Triticum aestivum L).
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