Variation in agronomic characters among high and low nitrogen S_2 maize (Zea mays L) lines grown in high and low nitrogen environments

摘要

Poor soil fertility, especially with low levels nitrogen (N), is a major constraint to productivity and the production of maize in Sub-Saharan Africa (SSA). This phenomenon has raised the need to combine the breeding goals of yield improvement for conditions with low levels of N and yield improvement for conditions with high input of N fertilizer. The objective of this study was to evaluate variation in agronomic characters, heritability, genotype x environment (GxE), and predicted gains from selection of high and low N S., maize breeding lines in both high and low N environments. Fertilizer was not applied in low N environments, while the high N environments were fertilized at the rate of 150 kg N, 75 kg P_2O_5 and 75 kg K_2O per hectare. The highand low N S_2 progenies were evaluated under high and low N environments respectively in the research farms of the Nigerian Institute for Oil Palm Research (NIFOR), near Benin City (Latitude 6o 33' N and Longitude 5°33'E), Edo State and Delta State College of Agriculture, Ozoro (latitude 6°13'E and longitude 5°33'N). Both locations are situated in the rainforest ecological zone of Nigeria with average rainfall of 2,500 mm. The experimental designs used for both high and low N environments were 10x10and 8x8 lattices respectively. The mean squares for the two high N environments were significant for all agronomic traits evaluated. Moreover, the mean squares for the high N S_2 progenies were significant for all the observed agronomic characters exceptear height and leaf senescence. The high N progenies x environments interaction was significant in most of the observed agronomic characters except leaf area, ear height and leaf senescence. On the contrary, the mean squares for the two low N environments were significant for all the observed agronomic characters except leaf senescence. Significant mean squares were observed among low N S_2 progenies in leaf area, ear height, leaf senescence and grain yield. However, there was no low N x environment interaction for all the observed agronomic characters. Grain yield of low N S2 progenies was only 5.46% of the yield obtained among high N S_2 progenies. Nitrogen stress resulted in reduction of growth (height) and yield of low N S_2 progenies by 52.3% and94.5%, respectively. Low N environments resulted in lower broadsense heritability than high N in most of the observed agronomic characters except plant height, leaf senescence and ear height. Heritability estimates in low N and high N ranged from -9.8 to 53.9% and -7.8 to 59.5%, respectively. The results indicated that the magnitude of genetic variance, heritability, and gains from selection are dependent on the nature of the crop environment. In spite of lower heritability under low N stress conditions, selection under low N would be more efficient than selection under high N for targeting low N stress environment.