Are cytological parameters of maize landraces (Zea mays ssp. mays) adapted along an altitudinal cline?

María Florencia Fourastié,Lidia Poggio,Alexandra Marina Gottlieb,Graciela Esther González

doi:10.1007/s10265-017-0996-3

Abstract

The Northwestern Argentina (NWA) highland region is one of the southernmost areas of native maize cultivation. We studied variations of different cytological parameters, such as DNA contents, presence/absence of B chromosomes (Bs), and number and sequence composition of heterochromatic knobs in ten accessions of four maize landraces growing along a broad altitudinal cline in NWA. The aim of this work was to assess variations in cytological parameters and their relationship with the crop altitude of cultivation, in an adaptive context. The A-DNA content of the A chromosome complements showed 40% of difference between the lowest (4.5pg) and the highest (6.3pg) 2C value. This variation could be attributed to differences in number and size of heterochromatic knobs. Fluorescent in situ hybridization studies revealed the sequence composition of each knob, with a higher proportion of knobs composed of 180-bp repeats rather than TR-1 repeats, in all accessions. We also found numerical polymorphisms and the highest frequency of Bs reported in maize to this date. These results lead us to propose that the frequencies and doses of Bs are influenced by the landrace genotypical make-up. The Bs might be maintained in higher frequencies in those accessions having lower heterochromatin content, so as to preserve an optimal nucleotype. Furthermore, selective forces acting along the altitudinal gradient might be modulating the cytological parameters studied, as suggested by the significant correlations found among them.

Highlights

Maize (Zea mays ssp. mays L., Poaceae) is widely distributed throughout the American continent, being grown in a variety of agro-ecological areas, from the lowlands up to the highland Andes (Kato et al 2009; McClintock et al 1981)
The aim of this work was to assess the variations in cytological parameters and their relationships with the cultivation altitude of Northwestern Argentina (NWA) maize landraces growing along a broad altitudinal cline, in order to determine the adaptive value of these parameters
We studied the genome sizes (2C values) of 10 accessions of four maize landraces grown along a broad altitudinal cline, ranging from 910 to 3900 m.a.s.l., in Northwestern Argentina

Summary

Introduction

Maize (Zea mays ssp. mays L., Poaceae) is widely distributed throughout the American continent, being grown in a variety of agro-ecological areas, from the lowlands up to the highland Andes (Kato et al 2009; McClintock et al 1981). Previous studies showed great variability in the DNA contents (2C values) of different maize inbred lines and landraces from the American continent, ranging from 4.87 to 7.11 pg (Díez et al 2013; McMurphy and Rayburn 1991; Rayburn 1990; Rayburn et al 1985, 1989, 1993; Rosato et al 1998; Tito et al 1991). The relationships between the DNA contents in maize landraces and their cultivation altitudes were assessed with contradictory results (Díez et al 2013; Rayburn 1990; Rayburn and Auger 1990; Rosato et al 1998). Negative correlations were detected in Southwestern USA populations and in landraces from the Andean NWA (Poggio et al 1998; Rayburn and Auger 1990; Rosato et al 1998), whereas a positive correlation was evidenced in USA populations. The DNA content has been associated with physiological features, such as vegetative period (interval from sowing to anthesis of tassel flowers), and cold and freeze tolerance, for which positive correlations were reported (Greilhuber and Leitch 2013; Poggio et al 1998; Realini et al 2016; Tito et al 1991)

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