Using whole-genome SNP data to reconstruct a large multi-generation pedigree in apple germplasm

Background Apple (Malus x domestica Borkh.) is one of the most important fruit tree crops of temperate areas, with great economic and cultural value. Apple cultivars can be maintained for centuries in plant collections through grafting, and some are thought to date as far back as Roman times. Molecular markers provide a means to reconstruct pedigrees and thus shed light on the recent history of migration and trade of biological materials. The objective of the present study was to identify relationships within a set of over 1400 mostly old apple cultivars using whole-genome SNP data (~253K SNPs) in order to reconstruct pedigrees. Results Using simple exclusion tests, based on counting the number of Mendelian errors, more than one thousand parent-offspring relations and 295 complete parent-offspring families were identified. Additionally, a grandparent couple was identified for the missing parental side of 26 parent-offspring pairings. Among the 407 parent-offspring relations without a second identified parent, 327 could be oriented because one of the individuals was an offspring in a complete family or by using historical data on parentage or date of recording. Parents of emblematic cultivars such as 'Ribston Pippin', 'White Transparent' and 'Braeburn' were identified. The overall pedigree combining all the identified relationships encompassed seven generations and revealed a major impact of two Renaissance cultivars of French and English origin, namely 'Reinette Franche' and 'Margil', and one North-Eastern Europe cultivar from the 1700s, 'Alexander'. On the contrary, several older cultivars, from the Middle Ages or the Roman times, had no, or only single, identifiable offspring in the set of studied accessions. Frequent crosses between cultivars originating from different European regions were identified, especially from the 19th century onwards. Conclusions The availability of over 1400 apple genotypes, previously filtered for genetic uniqueness and providing a broad representation of European germplasm, has been instrumental for the success of this large pedigree reconstruction. It enlightens the history of empirical selection and recent breeding of apple cultivars in Europe and provides insights to speed-up future breeding and selection

New Insight into the History of Domesticated Apple: Secondary Contribution of the European Wild Apple to the Genome of Cultivated Varieties

The apple is the most common and culturally important fruit crop of temperate areas. The elucidation of its origin and domestication history is therefore of great interest. The wild Central Asian species Malus sieversii has previously been identified as the main contributor to the genome of the cultivated apple (Malus domestica), on the basis of morphological, molecular, and historical evidence. The possible contribution of other wild species present along the Silk Route running from Asia to Western Europe remains a matter of debate, particularly with respect to the contribution of the European wild apple. We used microsatellite markers and an unprecedented large sampling of five Malus species throughout Eurasia (839 accessions from China to Spain) to show that multiple species have contributed to the genetic makeup of domesticated apples. The wild European crabapple M. sylvestris, in particular, was a major secondary contributor. Bidirectional gene flow between the domesticated apple and the European crabapple resulted in the current M. domestica being genetically more closely related to this species than to its Central Asian progenitor, M. sieversii. We found no evidence of a domestication bottleneck or clonal population structure in apples, despite the use of vegetative propagation by grafting. We show that the evolution of domesticated apples occurred over a long time period and involved more than one wild species. Our results support the view that self-incompatibility, a long lifespan, and cultural practices such as selection from open-pollinated seeds have facilitated introgression from wild relatives and the maintenance of genetic variation during domestication. This combination of processes may account for the diversification of several long-lived perennial crops, yielding domestication patterns different from those observed for annual species

La gestion des ressources génétiques des arbres fruitiers à pépins : vers la constitution d'une collection nationale

National audienc

Genetic diversity, Population structure, parentage analysis, and construction of core collections in the French apple germplasm based on SSR markers

In-depth characterization of apple genetic resources is a prerequisite for genetic improvement and for germplasm management. In this study, we fingerprinted a very large French collection of 2163 accessions with 24 SSR markers in order to evaluate its genetic diversity, population structure and genetic relationships, to link these features with cultivar selection date or usage (old or modern, dessert or cider cultivars), and to construct core collections. Most markers were highly discriminating and powerful for varietal identification, with a probability of identity P(ID) over the 21 retained SSR loci close to 10-28. Pairwise comparisons revealed 34% redundancy and 18.5% putative triploids. The results showed that the germplasm is highly diverse with an expected heterozygosity He of 0.82 and observed heterozygosity Ho of 0.83. A Bayesian model-based clustering approach revealed a weak but significant structure in three subgroups (FST = 0.014-0.048) corresponding, albeit approximately, to the three subpopulations defined beforehand (Old Dessert, Old Cider and Moderncultivars). Parentage analyses established already known and yet unknown relationships, notably between old cultivars, with the frequent occurrence of cultivars such as ‘King of Pippin’ and ‘Calville Rouge d’Hiver’ as founders. Finally, core collections based on allelic diversity were constructed. A large dessert core collection of 278 cultivars contained 90% of the total dessert allelic diversity, whereas a dessert sub-core collection of 48 cultivars contained 71% of diversity. For cider apples, a 48-cultivars core collection contained 83% of the total cider allelic diversity

Mean proportions of assignment to each of the two species in species pair comparisons (K = 2) including <i>M. domestica</i> (Genepool 1) and each of the four wild <i>Malus</i> species (Genepool 2).

<p>Mean proportions of assignment to each of the two species in species pair comparisons (K = 2) including <i>M. domestica</i> (Genepool 1) and each of the four wild <i>Malus</i> species (Genepool 2).</p