S1 and S2 selection of Longe 4 maize variety for tolerance to low soil nitrogen in Uganda

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%). For this purpose S1, S2 and S2R (S2 random) families derived from Longe 4; a popular early maturing OPV, were evaluated. Yield, yield components and other agronomic traits were assessed among families to compare mean performance of generations, to estimate heritability and the amount of genetic variance in the three samples, and to determine the magnitude of correlation between traits and between environments. Results obtained indicated that S1s in both testing environments yielded higher than S2s and gave larger predicted gains from selection. Genetic variances were higher for S1s in both environments; therefore, more rapid gains for yield in Longe 4 are expected from S1 compared to S2 selection. The overall yield reduction in the low-N test was 35% and 34% in 2009A and 2009B, respectively. Average broad sense heritability estimates under low N were 21% for grain yield, 17% for ASI (S2); narrow-sense heritability 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 S1 and S2 families which can be improved by selection. Selection should be done at S1 to save time and avoid an extra season of selfing and the associated resources required. Predicted gains were higher for S1 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.