Inheritance of nitrogen use efficiency components in maize

English: The general objectives of this research were to study the genetic variability for nitrogen use efficiency components, to identify suitable inbred parental lines with out standing nitrogen efficiency characteristics, to calculate the inheritance of nitrogen use efficiency (NUE) components and to develop a strategy for the development of nitrogen efficient maize hybrids. Four parental lines (AC8342, CML394, K64R and M162W) were individually crossed to each tester (CML351, CML202 and CML216) in a Line x Tester fashion to produce FI hybrids seed. The FI hybrids were evaluated in two different environments each under two different nitrogen levels. Six agronomic and yield characteristics and three nitrogen use efficiency components were measured. The data were analysed using the computer program' AGROBASE 2000'. Analyses such as Line x Tester, additive main effects and genetic correlations were performed. In the combined ANOVA, significant differences between locations were found for all characters measured. The nitrogen levels differed significantly for PLHT and GNC. The FI hybrids differed significantly for PLHT, GY, SDW, SDN and GNC. Significant differences were also found among the FI hybrids for PLHT, GY, SDW, SDN, HI, GNC and SNC at Doompan. Similar significant differences were observed at Bethlehem except for HI and SNC. Significant variability between FI hybrids was observed for yield efficiency, recovery efficiency and physiological efficiency. There was a large'" environmental difference between locations for the nitrogen use efficiency components. In the simple ANOVA, significant differences between FI hybrids were observed for yield efficiency, recovery efficiency and physiological efficiency at Doompan. Significant differences were also . found between the FI hybrids for yield efficiency and recovery efficiency at Bethlehem. With a few exceptions in the Bethlehem trial, the selection indices of the F, hybrids for PLHT were less than one. The selection index for GY exceeds the value of one in three and nine of the F, hybrids in the Doornpan and Bethlehem trials respectively. For SOW three of the F, hybrids in the Doornpan trial had values above one and nine of the F, hybrids in the Bethlehem trial. The selection index values for SDN were lower than one in the Doornpan trial. In the Bethlehem trial the values of three of the crosses were larger than one. The selection indices for HI in both trials were relatively high. At Ooornpan the F, hybrids responded significantly different to the two N-Ievels for PLHT, GY, SDW, SDN, HI and GNC. Significant differences between the F, hybrids at the low N-Ievel were found for all characters measured except for SNC. At the high N-level the F, hybrids differed significantly for PLHT, GY, SDW, SDN, HI and GNC. At Bethlehem, FI hybrids responded significantly different to the two N-levels for GY, SON and HI. Significant differences were found between the F, hybrids at both N-levels for PLHT, GY, SDW, SDN and GNC. At Doornpan significant differences existed between the F, hybrids for yield efficiency, recovery efficiency and physiological efficiency. At Bethlehem significant variability was found between the FI hybrids for all three nitrogen use efficiency components. The two N-Ievels had a significant effect on the GCA-values of the lines and testers for PLHT and SDN in the Doornpan trial. Significant variability was also found between the GCA-values for PLHT, GY and SDN at both N-levels. The GCA-values of the inbred lines in the Bethlehem trial responded differently to the two N-Ievels for GY and SON. Significant differences were found between the GCA-values of the inbred lines for PLHT at both N-Ievels and for GY only between the testers at the high N-Ievel. At Doornpan significant differences between the GCA-values of the lines were found only for physiological efficiency and between the testers for yield efficiency and recovery efficiency. At Bethlehem the GCA-values for testers differed significantly for yield efficiency and recovery efficiency. No significant differences were found between. the GCA-values of the lines for nitrogen use efficiency components at Bethlehem. The FI hybrids responded differently with regard to their SCA-values for GY, SOW. HI, GNC and SNC in the Doornpan trial. Significant differences for SCA-values were found for PLHT, GY, SOW, SON and SNC at both N-Ievels. In the Bethlehem trial the two N-levels had only an effect on the SCA-values of a few of the hybrids for SON and GNC. Significant differences were found between the SCA-values of the FI hybrids for PLHT, GY, SOW, SON and GNC at both the low and the high N-Ievels. The F I hybrids showed significant differences between the SCA-values for all three nitrogen use efficiency components in the Doornpan trial and only for yield efficiency and recovery efficiency in the Bethlehem trial. The GCA:SCA ratios differed significantly at the two N-levels for PLHT in the Doornpan trial. With the exception of SON the additive variance components of SOW, GNC and SNC were higher at the high N-level. In the Bethlehem trial the GCA:SCA ratios for PLHT, SDW and GNC were higher at the high N-level. SOW had the largest GCA:SCA ratios under both N-levels. The GCA:SCA ratios for recovery efficiency was larger than that of yield efficiency. In the Doornpan trial the narrow-sense heritabilities for PLHT and GNC were the largest under the high N-level. The narrow-sense heritabilities for nitrogen use efficiency components were very low. The narrow-sense heritabilities of PLHT, GY, SOW, GNC and SNC were much larger at the high N-Ievel at Bethlehem. Again the heritabilities obtained for nitrogen use efficiency components were very low. Significant phenotypic correlation coefficients were found between GY and PLHT at the high N-Ievel in the Doompan trial. Significant correlation coefficients were also found between GY and SDN at both N-Ievels. In the Bethlehem trail significant correlation coefficients existed between GY and PLHT and between GY and SON at both N-levels. GNC was significant but negatively correlated with GY at the high N-level. The genotypic correlation coefficients in the Doompan trial were significant between GY . and SDN and between GY and SNC at both N-Ievels. HI and GY were significantly correlated at the high N-Ievel. In the Bethlehem trial SDN was highly correlated with GY at both N-levels. GY was significantly correlated with PLHT at the high N-level, negatively correlated with SDW at the low N-Ievel and negatively correlated with GNC at the high N-Ievel. In the Doompan trial GY at the low arid the high N-levels was significantly correlated with yield efficiency. It was also significantly correlated with recovery efficiency at the high N-level. In the Bethlehem trial GY was significantly correlated with the three nitrogen use efficiency components at the high N-level. Recovery efficiency was significantly correlated with GY at the low N-level.