Cytogenetic diversity in maize landraces shaped by long-term cultivation and ecogeographic adaptation.

This study characterizes the cytogenetic diversity of maize landraces from Northern Argentina, a region comprising Northwestern Argentina (NWA) and Northeastern Argentina (NEA). New data from four NWA landraces were analyzed using DAPI banding, fluorescence in situ hybridization, and flow cytometry. Intra- and inter-populational variation was detected in heterochromatin content (2.06%-12.6%), as well as in the number (3-15), size, and chromosomal position of knobs. Genome size (2C value) ranged from 5.27 to 5.74 pg, and numerical polymorphism (0-2) of B chromosomes was observed. Consensus idiograms were constructed for each studied landrace. A quantitative analysis combining these data with previously published information on Argentine maize revealed a negative association between knob heterochromatin content and cultivation altitude. In NWA landraces, genome size was also negatively associated with altitude, whereas no such relationship was detected when NWA and NEA data were analyzed together. In NEA landraces, which grow within a narrow altitudinal range, genome size variability may be influenced by local farmers selection practices, whereas in NWA landraces cytogenetic variation may reflect multifactorial anthropogenic and environmental influences. B chromosomes were recorded exclusively at altitudes above 2000 m.a.s.l. The observed cytogenetic patterns are discussed in the context of ecogeographic differentiation among maize landraces.