| Diallel analysis for combining ability over environments
in wheat I. SINGH, R.S. PARODA 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 3 m rows and at 30 x 15 cm row to row and plant to plant distance, respectively. From each entry (prarent 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, 1,000-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 headidg, indicating thereby the sensitivity of both kinds of gene effects to the environmental variations. However, relatively higher magnitude of gca x enviroments 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 & JOSHI 1970a, b ; PARODA & HAYS 1971 and SHARMA & 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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