GENETIC ANALYSIS FOR NITROGEN USE EFFICIENCY AND YIELD ASSOCIATED TRAITS IN BREAD WHEAT

Abstract

Development of nitrogen (N) efficient bread wheat cultivars better suited to limiting nitrogen condition is one of the prime objectives in plant breeding research. Three years (2013/14, 2014/15 and 2015/16) study was carried out to investigate genetic variability, identify traits influencing N use efficiency (NUE) and their pattern of inheritance using Hayman and Griffing approaches at The University of Agriculture, Peshawar Pakistan. During 2013/14, 30 wheat varieties released during 1981 till 2013 were preliminary screened under high nitrogen (Recommended dose, N+) and low nitrogen (N0) conditions as independent experiments. Significant G×E for all traits justified independent analysis. Independent analysis revealed significant genotypic variation for all traits under each level of nitrogen. Significant reductions under N0 condition for all traits signified the role of nitrogen fertilization in crop production. Path coefficient analysis identified biological yield, grain nitrogen content, harvest index and grain growth rate as direct contributors, whereas, tillers m-2 and 1000 grains weight, biological growth rate, total nitrogen uptake and nitrogen harvest index as indirect contributors for the improvement of NUE in bread wheat. Based on stress selection indices, cluster analysis, principal components analysis and 3D biplot analysis Shahkar-13 (Shk), Pirsabak-05 (PS) and Tatara (Tat) were classified as N-efficient, while Hashim-08 (Hsm), Inqilab-91(Inq) and Pak-81 (Pak) were found as N-inefficient varieties. During 2014/15, an objectives-based hybridization program was initiated by crossing two contrasting groups of varieties to generate a 6 × 6 straight diallel. In the following year, 15 F1 hybrids along with six parent cultivars were evaluated under N+ and N0 conditions. Significant GEI for all traits necessitated independent analysis under each nitrogen level, which exhibited significant variation among genotypes justifying genetic analysis for all traits. Diallel analysis of variance exhibited preponderance of non-additive gene action in the inheritance of all traits under both N+ and N0 conditions. However, non-additive genetic effects for days to emergence, anthesis, maturity and grain filling duration were changed to additive genetic control under N0 condition. Pre-dominant role of non-additive genetic effects was further validated by the greater proportion of dominance than additive genetic variance, higher magnitude of H1 than D genetic component, proportion of dominant genes, average degrees of dominance (>1), Wr/Vr graphs and low narrow sense heritability. Position of parents along the regression line expressed that Tatara20 96 and Hashim-08 possessed more dominant and recessive genes, respectively for most of the traits. Heritability estimates both in narrow and broad sense were greater under N+ than N0 condition for most of the traits. Low to moderate ratio of narrow and broad sense heritability for most of the traits exhibited that non-additive variance was predominant than additive variance in the expression of these traits. Combining ability analysis revealed the significance of both GCA and SCA effects for almost all traits. Traits with GCA/SCA ratio less than 1 indicated importance of non-additive genetics effects in phenotypic expression of these traits. Tatara appeared as best general combiner for all important NUE and yield associated traits. Relative ranking of crosses for SCA effects were not the same under both N+ and N0 conditions. The F1 hybrid, Shk × Hsm expressed maximum SCA effects for most of the important traits under both N+ and N0 conditions, whereas, PS × Shk was ranked as top specific combination for most of the traits only under N0 condition. Correlation analysis suggested that mean values of both parents and F1 hybrids predict their suitability as general or specific combiner. Better parent heterosis was exhibited by cross combinations Shk × Hsm and PS × Tat for most of the important traits under N+ and N0 conditions, respectively. Both Hayman and Griffing analyses revealed the involvement of non-additive gene actions in the phenotypic expression of most of the traits. Non-additive genetic variance of traits warranted improvement through delayed selection. Besides exploring genetics of N-efficient lines, this study also identified some indices for selecting N-efficient wheat lines. Cross combinations Shk × Hsm, PS × Shk and PS × Tat with higher SCA and heterobiltiosis may be useful in evolving wheat cultivars with enhanced NUE.