Genotypic variation and relationships among traits for root morphology in a panel of tropical maize inbred lines under contrasting nitrogen levels

A strategy to increase nitrogen (N) use efficiency in maize is the genetic improvement of N acquisition through root morphology. Here, we quantified the genetic variation of 150 tropical maize inbred lines for root morphology and shoot traits and investigated the relationships among traits. We evaluated the inbred lines at the seedling stage in a greenhouse experiment under two treatments: high N and low N supply. A mixed model approach was used to estimate variance components. Canonical correlations were estimated between root- and shoot-related groups of traits, and the genetic diversity among inbred lines was determined. Our inbred line panel showed huge genetic variability for all traits and presented large genetic diversity under both N levels. Root dry weight (RDW) was associated with shoot dry weight (SDW) at high N, and RDW and total root length (TRL) were positively associated with SDW at low N. Based on SDW, RDW and TRL, we selected a set of the top 15 maize inbred lines to be used in maize breeding programs focusing on N-use efficiency. We therefore concluded that there is a significant diversity in tropical maize inbred lines, which have the genetic potential to produce N-efficient hybrids and maize breeding populations for N stress conditions.