Teosinte in Europe - Searching for the Origin of a Novel Weed

Abstract

A novel weed has recently emerged, causing serious agronomic damage in one of the most important maize-growing regions of Western Europe, the Northern Provinces of Spain. The weed has morphological similarities to a wild relative of maize and has generally been referred to as teosinte. However, the identity, origin or genetic composition of 'Spanish teosinte' was unknown. Here, we present a genome-wide analysis of single-nucleotide polymorphism (SNP) data for Spanish teosinte, sympatric populations of cultivated maize and samples of reference teosinte taxa. Our data are complemented with previously published SNP datasets of cultivated maize and two Mexican teosinte subspecies. Our analyses reveal that Spanish teosinte does not group with any of the currently recognized teosinte taxa. Based on Bayesian clustering analysis and hybridization simulations, we infer that Spanish teosinte is of admixed origin, most likely involving Zea mays ssp. mexicana as one parental taxon, and an unidentified cultivated maize variety as the other. Analyses of plants grown from seeds collected in Spanish maize fields and experimental crosses under controlled conditions reveal that hybridization does occur between Spanish teosinte and cultivated maize in Spain, and that current hybridization is asymmetric, favouring the introgression of Spanish teosinte into cultivated maize, rather than vice versa.

Figure 1

PCA of maize, teosinte and hybrid samples collected in Spain. Samples were collected from plants growing in the field (black labels), from seeds collected in the field and subsequently grown in a climate chamber (grey labels) or from reference material (grey labels). Labelled symbols represent own data that were compared to other publically available data (without labels) (27′476 SNPs and 662 individuals).

Figure 2

PCA of teosinte samples grown from the seeds obtained as a reference material. Labelled symbols represent own data that were compared to other publically available data (without labels) (27′476 SNPs and 280 individuals).

Figure 3

STRUCTURE analysis of Spanish maize varieties, hybrids, Spanish teosinte, Z.m. ssp. mexicana and ssp. parviglumis. Bar plot of assignment proportions at K = 6 combining own SNP data and other publically available data (27′476 SNPs and 360 individuals).

Figure 4

PCA of simulated hybridization between Spanish maize varieties and Z.m. ssp. mexicana. Coloured symbols represent empirical data (27′476 SNPs and 360 individuals) and black symbols represent simulated data.

Figure 5

Basic morphological differences between Spanish commercial maize, hybrid and Spanish teosinte plants. Plants were grown in a climate chamber from seeds collected in the field in Spain.