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Diallel analysis for combining ability
over environments in wheat
Iqbal SINGH, R. S. PARODA1) and R. K. BEHL
Department of Plant Breeding Haryana Agricultural
University, Hisar, India
Phenotypic expression of quantitative characters is highly
influenced by environmental fluctuations. Genotype x
environment interaction, depending upon their nature and
magnitude, leads to bias in the estimates of gene effects
and combining ability for various characters sensitive to
environmental modulations. Such traits are less amenable to
selection. It is, therefore, necessary to assess the
sensitivity of estimates of gene effects under variable
environmental conditions so as to ensure better prediction
and gain under selection. Present study deals with such an
endeavours.
Materials and Methods
The experimental material consisted of parental and
F1 generations of a 9 x 9 diallel set (excluding
reciprocals) of spring wheat (Triticum aestivum L.
em. Thell). The experimental material was laid out in a
randomized block design with three replications in two
environments, namely, normal (irrigated) and stress
(rainfed). The nine parents included were WL 711, NP 846, WG
377, HD 1981, UP 262, HD 1925, HD 2122, Raj 821 and
Sonalika. Single seeds were sown in 3m long rows and at 30 x
15 cm row to row and plant to plant distance, respectively.
From each entry (parent and F1) five competitive
plants were randomly selected from each replication in both
the environments for recording observations on characters
days to heading, plant height, tiller number, total biomass,
number of grains/ear, 1000-grain weight and grain
yield/plant. Pooled analysis for combining ability was
carried out following Method 2, Model 1 of Griffing (1956)
as extended by Singh (1973).
Results and Discussion
Pooled analysis of variance over the environments (Table
1) revealed highly significant differences amongst them.
So was true for genotype x environment interactions.
The pooled analysis of variance for combining ability
reflected that both the general combining ability (gca) and
specific combining ability (sca) mean squares were
significant. Thus, both kinds of gene effects figured
important in controlling inheritance of all the characters
studied. Both gca x environments as well as sca x
environments interactions were significant for all the
characters except sca x environments for days to heading,
indicating thereby the sensitivity of both kinds of gene
effects to the environmental variations. However, relatively
higher magnitude of gca x environments interactions as
compared to sca x environments interactions suggested a
higher sensitivity of gca to environments than that of sca.
Similar results were obtained by Paroda and Joshi, 1970a, b;
Paroda and Hays, 1971 and Sharma and Singh, 1982. Perhaps
the heterozygosity per se and physiological
advantages attached hitherto by virtue of heterosis or
enhanced metabolic rates (Sinha & Khanna, 1975) have
contributed to lower sensitivity of sca to environmental
fluctuations as compared to gca.
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