Phenotypic Diversity of Root Anatomical and Architectural Traits in Zea Species

We characterized phenotypic variation for root traits in 256 Zea spp. accessions, including maize landraces and Z. mays L. subsp. huehuetenangensis (H. H. Iltis & Doebley) Doebley, subsp. mexicana (Schrad.) H. H. Iltis, and subsp. parviglumis H. H. Iltis & Doebley, Z. nicaraguensis H. H. Iltis & B. F. Benz, Z. perennis (Hitchc.) Reeves & Mangelsd., and Z. luxurians (Durieu & Asch.) R. M. Bird. Anatomical traits included areas of the cross-section, stele, cortex, aerenchyma, and xylem and number of cortical cells and cell files. Architectural traits included diameters of the nodal root system, individual crown roots, and the stem; numbers of seminal and nodal roots; biomass; and nodal root length and branching. Ranges for anatomical traits were similar for teosintes and landraces, except for aerenchyma and xylem areas, and number of cortical cells. Landraces had greater variation for architectural traits except for nodal root number and branching, and had larger mean stele and xylem areas, longer nodal roots, wider nodal systems, and more seminal roots than teosintes. In contrast, teosintes were smaller but had more nodal roots with greater branching. At a common plant size, teosintes would have lower mean values for all anatomical traits, except for number of cortical cells and cell files. Teosintes had greater scaled values for all architectural traits except average root diameter. Cluster analysis divided accessions into eight root phenotypes. Phenotypic diversity for root traits in the genus Zea could be a valuable resource for improving stress tolerance in maize.