Abstract:

Low nitrogen is a major environmental stress leading to low yields in maize. Identification of varieties able to perform well under low soil N is of great significance to
the resource poor farmers in the country especially when input costs are high and
fertilizer use is very low (3%). This study was conducted with the following objectives;
(1) to compare the yield performance of Longo 4 families in S, and S2 generations under
low and optimal N conditions, (2) to estimate the heritability of yield in S, & So
generations and (3) predict expected gain under low N conditions for different selection
approaches and to determine the association of yield with key secondary traits for
possible use in indirect selection to improve yield. For this purpose Si, So and SoR (So
random) families derived from Longe 4; a popular early maturing OPV, were evaluated during the 2 growing seasons of 2009A and 2009B at National Crops Resources Research Institute (NaCRRI) under low and optimal nitrogen conditions. Sj-derived S2
families were randomly selected (SoR) to produce an unselected control population using a random number generation procedure. Yield, yield components and other agronomic trails were assessed among families to compare mean performance of generations, to
estimate heritability and the amount of genetic variance in the three populations, and to
determine the magnitude of correlation between traits and between environments. Results
obtained indicated that S, families in both testing environments yielded higher than So
families and gave larger predicted gains from selection. Genetic variances were higher for S1 families in both environments. Therefore, more rapid gains for yield in Longe 4 arc expected from S, compared to S2 selection. The overall yield reduction in the low-N test
was 35% and 34% in 2009A and 2009B, respectively. However, some SI families performed well in both low N and optimum N experiments. Average broad sense herilability estimates under low N were 21% for grain yield, 17% for ASI (S2), 18% for ears per plant, 18% for leaf senescence and 21% for yellowing. Narrow-sense herilability was 0.24 and 0.52 for grain yield and ASI respectively. Genotype means under low N showed correlations between grain yield and: ASI, -0.23; plant height, 0.52; leaf
senescence, 0.15 and leaf nitrogen concentration, 0.12. In conclusion, sufficient amount
of genotypic variation was found for low N tolerance among Longe 4 S, and Si families
which can be improved by selection. Selection should be done at S, to save time and
avoid an extra season of selfing and the associated resources required. Predicted gains were higher for Si families and when ranks of grain yield were averaged across N-levels, therefore both environments should be used in selection of genotypes for low nitrogen
performance if feasible.