Physiological and Morphological Changes Associated with Recurrent Selection for Grain Yield in Maize Under Low and High Nitrogen Conditions.

Increase in grain yield of maize in West Africa can be achieved by developing maize varieties tolerant to low nitrogen (N) and improving soil fertility. Six maize populations were evaluated in two locations in Nigeria  under low-N (45kgN/ha) and high-N (90kgN/ha) conditions to identify morphological and physiological traits that changed in genotypes that had undergone some cycles of recurrent selection for tolerance to low soil nitrogen and to determine the relationship between physiological and yield traits in both nitrogen environments. Results revealed that improved cycles of three populations displayed longer leaf area duration (LAD), larger leaf area index (LAI) and higher crop growth rate (CGR) at silking than their earlier versions at 45kgN/ha and 90kgN/ha . Net assimilation rate (NAR) increased significantly with response to selection in three out of six populations at 45kgN/ha. Significant yield changes were observed in response to selection in three populations at 45kgN/ha and four populations at 90kgN/ha, accompanied by increments in 100 grain weight in three populations and number of kernel per row in one population. Grain yield and 100 kernel weight reduced by 31% and 5% respectively in response to N-stress. Among physiological traits, only CGR and SPAD readings had significant positive relationship with grain yield under low and high nitrogen conditions. Hence, CGR and SPAD values at silking could be utilized in selecting for tolerance to low-N in maize for this region.

Key words: Grain yield, physiological traits, recurrent selection, nitrogen, maize