| Combining ability anaiysis over environments in spring
wheat M.S. YADAV and I. SINGH Department of Plant Breeding, Hayana Agricultural University, Hisar, India Environmental fluctuations highly influence the phenotypic expression of quantitative traits. Genotypic 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 be improved through selection. There are few reports available regarding the environmental effects on the estimates of gene effects and combining ability in wheat. The present investigation was, therefore, undertaken to drive information on the nature of gene effects and combining ability operative in the inheritance of different economic traits and also to detect the role of environmental components on the sensitivity of estimates of gene effects so as to ensure better prediction and gain under selection. Materials and Methods The eight genetically diverse lines, originating from different agro-climatic zones, included in the present investigation were HD 2285, WH 147, WH 291, WH 283, CPAN 1907, CPAN 1830, HD 2009 and HW 517. These lines were crossed in all possible combinations (excluding the reciprocals). The 36 genotypes (8 parents and 28 F1 s) were grown durinrg the winter of 1984-85 in a randomized block design providing three replications in two environments i.e., normal (irrigated and timely sown) and stress (irrigated and late sown). The plant to plant and row to row spacings were kept at 15 and 30 cm, respectively, and the length of the row was 3 m. The data were collected on five randomly selected plants from each replication in each row for days to heading, plant height, tiller number, total biomass, number of grains/ear, 1000-grain weight, grain yield/plant and harvest index (ratio between the economic and biological yields). The combining ability analysis was carried out following GRIFFING (1956) and the combining ability in environment interaction effects were computed following SlNGH (1973). Results and Discussion Analysis of vairance over the environments showed highly significant differences due to environments for all the characters, indicating sufficient diversity among the measured environments. The genotypes and environment x genotypes were also significant for all the characters (Table 1). 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 i.e., additive and non-additive appeared to be important in controllinrg the inheritance of all the characters. This warrants some kind of population improvement approach as earlier suggested by JENSEN (1970). Both gca x environments as well as sca x environments interactions were significant for au the characters except gca x environments for 1000-grain weight, indicating thereby the sensitivity of both kinds of gene effects to the environmental variations except for 1000-grain weight for which only non-additive gene effects were sensitive. For the characters days to heading, plant height, number of grains/ear and grain yield/plant, there was higher magnitude of gca x environments interactions as compared to sca x environments interactions, suggesting a higher sensitivity of gca to environments than that of sca for these characters. Similar results were reported by PARODA & JOSHI 1970, PARODA & HAYS 1971, SHARMA & SINGH 1982 and SINGH et al. 1986. Perhaps the heterozygosity per se and physiological advantages attached hitherto by virtue of heterosis or enhanced metabolic rates (SINHA & KHANNA 1975) has contributed to lower sensitivity of sca to environmental fluctuations as compared to gca. While, rest of the characters i.e., tiller number, total biomass, 1000-grain weight and harvest index exihibited higher sensitivity of sca to environments than that of gca. |
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