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Accueil du site → Doctorat → Afrique du Sud → 2007 → INHERITANCE OF NITROGEN USE EFFICIENCY COMPONENTS IN SOUTH AFRICAN IRRIGATED WHEAT

University of the Free State (2007)

INHERITANCE OF NITROGEN USE EFFICIENCY COMPONENTS IN SOUTH AFRICAN IRRIGATED WHEAT

Otto, Willem Morkel

Titre : INHERITANCE OF NITROGEN USE EFFICIENCY COMPONENTS IN SOUTH AFRICAN IRRIGATED WHEAT

Auteur : Otto, Willem Morkel

Université de soutenance : University of the Free State

Grade : Philosophiae Doctor 2007

Résumé
In a second experiment, the NUE components of seven parental irrigation cultivars and their F2-offspring were studied in 2004 at a cooler (Bethlehem) and a warmer (Vaalharts) irrigation environment. The genotypes were tested at two N treatments ; a control (LN) and 180 kg N/ha (HN) applied. Agronomic characteristics, N uptake and NUE components were measured. From the analysis of variance, the agronomic characteristics (BM, grain yield, HM, TKM and GP) showed significant genotypic variation. Harvest index, BM, HM and TKM showed no significant genotypic variation at the N treatment. The N uptake and NUE components showed significant genotypic variation with the exception of NutEYld. The HN treatment resulted in significant variation in Ngrain, Ntotal NHI, NUEYld and NutEYld. The HN treatment increased BM, grain yield and GP values, but reduced the HM, TKM, HI and NHI values of the genotypes. The NUE components NupE%, NUEYld and NutEYld were also reduced by the HN treatment. Cultivars responded differently at the two N treatments in measured and calculated agronomic and NUE components. Olifants, Kariega and Marico showed good responses for the agronomic components at the HN treatment. Inia, SST 806, SST 822, Olifants, Kariega and Marico showed high values for NUE components. The crosses Olifants x Steenbras, SST 806 x SST 822, Marico x Steenbras, Olifants x SST 822 and Marico x SST 806 showed positive responses in the measured agronomical and NUE components. The correlation coefficients were calculated to study the phenotypic resemblance between characteristics. The calculated correlation matrixes for the environments indicated positive correlation coefficients between several of the agronomic and calculated components. Biomass and grain yield was highly correlated with the NUE components, NupE%, NUEYld, Ngrain and Ntotal at both environments. Grain protein was negatively correlated to NutEYld, while NHI was positively correlated to this component. This points to the first order importance of grain yield production before grain protein under limiting N availability conditions. The correlation coefficients of components BM, grain yield, NPE, NRE and NUEYld increased at the HN treatment. The effect of N treatments on the calculated GCA and SCA effects was studied from a diallel analysis. Significant GCA effects for the parental cultivars were found for the majority of the agronomic and NUE components at both N treatments. Significant SCA effects for the tested hybrids were also found at BM, grain yield, Ngrain, Ntotal, NupE%, NUEYld, NAEYld, PHE and NRE. The application of N fertilizer (LN versus HN treatments) affected the significance of the calculated combining abilities. For the agronomic characteristics that were measured at Bethlehem, GCA effects for BM, HM, TKM, GP and HI were significant at the HN treatment. Significant GCA effects were found at the LN treatment for TKM and GP. The N uptake components Ngrain, Ntotal and NHI showed significant GCA effects at the HN treatment. For the NUE efficiency components significant GCA effects were calculated for NupE%, NUEYld and NutEYld at the HN treatment. No significant cultivar differences were found for the N uptake and NUE components at the LN treatment. For the agronomic components SST 822, Inia and Kariega generally had the highest GCA values. The cultivars Marico, Olifants, SST 806 and Inia showed the highest GCA values at the HN treatment for the agronomic, N uptake and NUE components. At Vaalharts significant variability for GCA effects for the agronomic components BM, grain yield, HM, TKM and HI were found at both N treatments. For the N uptake components, significant GCA effects were calculated for Ngrain and Ntotal at both N treatments and for NHI at the HN treatment. Significant GCA effects were found for the NUE components NupE%, NUEYld at both N treatments and for NutEYld at the HN treatment. The cultivars Kariega, Olifants, Inia, Steenbras and SST 806 had the highest GCA values for the agronomic, N uptake and NUE components at the LN treatment. At the HN treatment Olifants, SST 806 and Inia had the highest GCA values for these components, as well as for the N uptake and NUE components. The calculated SCA effects at Bethlehem were significant for BM, grain yield, Ngrain, Ntotal, NUEYld at both N treatments, and for NAEYld, NPE, NRE, HM and NupE% at the HN treatment. At Vaalharts significant SCA effects were calculated for BM, grain yield, Ngrain, Ntotal, NupE%, NUEYld at both N treatments and for NHI at the HN treatment. The calculated GCA:SCA ratios for the respective components at Bethlehem showed that the values for most of the components increased at the HN treatment, with only grain yield, Ngrain and NUEYld at values less than one. The calculated NUE components NAEYld, NPE and NRE also showed non-additive gene action. At Vaalharts all the components showed additive gene action at both the LN and HN treatments, except for GP, NHI and NutEYld at the LN treatment. Also, in contrast to the response calculated at Bethlehem, the calculated NAEYld, NPE and NRE showed additive gene action. These differences in responses between the two environments can be attributed to the different growing conditions and N availability scenarios inducing the changes in response of agronomic and NUE components. High broad-sense heritabilities were calculated for BM, grain yield, HM, TKM and HI at the LN and HN treatments at both environments. At Vaalharts the heritability value for GP was high at the HN treatment, and at Bethlehem at both the LN and HN treatments. Broad-sense heritability estimates improved at the HN treatment except for TKM compared to the LN treatment. The heritability values for the N uptake components, Ngrain, Ntotal and NHI were high, and were increased at the HN treatment. With the exception of the NutEYld component at the LN treatment at Vaalharts, the broad-sense heritability values of all the NUE components were high and increased by the HN treatment. At Bethlehem the narrow-sense heritability value of TKM was high at both N treatments, and values of GP, NHI and NutEYld at the HN treatment. At Vaalharts high narrowsense heritability values were found for HM, TKM, NAEYld and NPE at the LN treatment. All the agronomic characteristics and calculated components showed increased narrowsense heritability values at the HN treatment. These responses indicate that the estimation of heritability of the studied components were improved when N were sufficiently available.

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