Single nucleotide polymorphism-based parentage analysis and population structure in garden asparagus, a worldwide genetic stock classification

Knowledge of genetic diversity and population structure in breeding material could be of great importance for crop improvement. Inheritance of molecular markers has been proved to be a powerful tool for verifying or discovering the parentage of cultivars in several crops. The present study aimed to undertake an extended parentage analysis using a large sample of garden asparagus (Asparagus officinalis L.) cultivars based on single nucleotide polymorphism (SNP) markers. In the past, asparagus cultivars began to be classified according to the countries and towns where they were grown. Among them, Violet Dutch is one of the oldest asparagus cultivars, considered to be the genetic stock from which several modern cultivars were derived. Starting from Violet Dutch, the breeding programs branched in two directions, yielding Argenteuil and Braunschweiger varieties in France and Germany, respectively. These lines became very important in all breeding programs, replacing older populations and landraces. This could account for the narrow genetic basis of cultivated asparagus, but in fact very few molecular marker studies have confirmed this hypothesis to date. In the present paper, using a new set of 144 SNPs, genetic relationships were investigated within an important collection of anther donor asparagus genotypes and a large panel of Italian double haploids (DHs) extensively used in the Italian and international breeding programs over the last 30 years. The results were useful for confirming the narrow variability of modern asparagus germplasm and for comparing the pedigree notes with genetic analyses. The results of this work showed that the DH collection includes two main and distinct genetic backgrounds, likely derived from Argenteuil and Braunschweiger genetic stocks, as expected. Moreover, the genetic analyses showed that the cv. Mary Washington, previously indicated as being derived only from Argenteuil, has a mixed origin from the two main genetic stocks. In addition, the present study underlines how this cultivar plays a central role in the pedigree of many modern cultivars/hybrids, giving new impact to the pedigree notes already described taking into account the large number of DHs derived from Mary Washington.