Genetic determinants of aerial root morphology in Sierra Mixe-derived maize

We mapped key regions of the maize genome that influence the formation of aboveground (aerial) roots, which in some varieties have been associated with symbiosis with nitrogen-fixing bacteria. Modern agriculture relies heavily on chemically synthesized nitrogen fertilizers, which ensure high yields but also carry high economic and environmental costs. Biological nitrogen fixation (BNF) supplies high amounts of nitrogen to legumes, and several avenues of research are underway to extend it to cereal crops. In maize, aerial roots formed in Sierra Mixe landraces have been associated with BNF. However, much of the genetics underlying aerial root morphology remains unknown. Here, we evaluate aerial root morphology traits associated with BNF in three segregating populations derived from crosses between two Midwest-adapted inbred lines and three landraces. Inclusive composite interval mapping (iCIM) with flowering time as a covariate identified 37 quantitative trait loci (QTL) for three aerial root traits (nodes with roots, root size, and roots per node) which exhibit moderately high heritability (H² = 0.65 to 0.83). The combined proportion of phenotypic variance explained by the detected QTL ranged from 23 to 51%, depending on the trait and population, and potential candidate genes were identified through literature searches, macrosynteny, and gene expression analyses. Introgressing the most relevant aerial root-associated QTL into elite genotypes may provide a path toward achieving meaningful levels of BNF-associated traits in maize, but further work is needed to assess this approach's viability under field conditions.