Swiss maize (Zea mays L) landraces. Their genetic diversity and distinctiveness in a global comparison

Abstract

Swiss maize landraces are expected to be genetically diverse, as they have been cultivated in different climatic regions of Switzerland for almost 500 years. A core collection of 35 Swiss maize landraces was recently defined. This core collection was analyzed in the present study, with the objectives (i) to resolve genetic diversity and phylogeny of the core collection, (ii) to relate these results to those obtained in a worldwide collection of maize landraces, thereby (iii) analyzing separation and admixture and (iv) to identify unique alleles that were detected only in Swiss maize landraces (Swiss alleles). A high diversity (HT = 0.61) in an international comparison and many Swiss alleles pointed at the value of this core collection as a plant genetic resource. The genetic differentiation within the core collection was in very good accordance with the geographic separation caused by the Swiss Alps. The accessions grouped into three major clusters, two northern and a southern one. Additionally, landraces from Valais built an intermediate cluster, which is probably the result of hybridization between different European germplasm. Continuous maize cultivation in remote areas may have favored genetic drift and intentional selection by farmers and may have led to this particular cluster. In the international comparison, northern Swiss accessions were related to European and American Northern Flints, whereas southern Swiss accessions were closely related to southern European Flints (e.g. Italian Orange Flints). Some northern Swiss accession combined high diversity with many Swiss alleles, which may be valuable for broadening the European Flint pool.