Response of Expired Plant Variety Protection Lines and Public Inbred Lines to Nitrogen At Seedling Stage.

Selecting for genotypes with high nitrogen use efficiency (NUE) can reduce nitrogen application rate and hence can address economic and ecological problems. Previous studies showed that genotypes with better root development have good nutrient acquisition and consequently high NUE.  The current study aimed at studying the genotypic variation of 14 root traits possibly having influence on NUE. Moreover this study aimed at setting recommendations for plant breeders to select genotypes with high potential for NUE breeding program depending on root traits at seedling stage. For this purpose, 74 diverse inbred maize lines were screened under two contrasting nitrogen levels (low and high nitrogen) in two independent experimental conditions. Preliminary results showed that there was a significant increase in shoot and root weight by increasing nitrogen level in nutrient solution. However lines responded different under different nitrogen levels. Based on biomass of shoots and roots, the genotypes were classified into four groups: efficient-responsive, efficient-non responsive, non efficient-responsive and non efficient-non responsive indicating high level of genetic variability among studied lines in response to nitrogen application during seedling stage. Significant medium to high associations were found between root and shoot weights and between plant biomass and other shoot and root related traits.  Genetic variance was significantly high for all measured parameters, while genotype×nitrogen interaction was low indicating that lines performing well under nitrogen stress can perform well under optimum nitrogen condition, and vice verse. Combined analysis of variance over experiments and nitrogen levels showed that heritability values for shoot and root biomass were 0.80 and 0.85 respectively. In conclusion, our results showed that the expired plant variety protection lines and public inbred lines are a rich source of variation for seedling root traits related to NUE. Development of single nucleotide polymorphic markers associated with root development is in progress.