Hybridization and Genetic Diversity in Wild Apple (Malus sylvestris (L.) MILL.) from Various Regions in Germany and from Luxembourg

Abstract

Malus sylvestris is the only apple species native to Central Europe. Its genetic integrity may be threatened by hybridization with the cultivated apple (Malus × domestica). A total of 883 genotypes, 477 putative wild apples in Germany and Luxembourg and 406 old to modern cultivars has been investigated. Wild apples growing in Germany originated from Rhineland-Palatinate, North Rhine-Westphalia, Saxony-Anhalt and Saxony. The genetic structure was analysed at ten isozyme marker loci, and morphology was studied by fruit size, leaf pubescence, and a complex morphological description performed in advance. A model-based cluster analysis applied to all nuclear data resulted in two clearly differentiated gene pools for putative wild and cultivated apples with moderate proportions of admixture in the wild group on average (0.138 total, 0.111 German sample). At the individual level, the percentages of both hybrids and feral cultivars together ranged from 2.3% in Rhineland-Palatinate to 28.8% in Luxembourg. The intraspecific variability in fruit diameter ranged from 21 to 40 mm, and that in leaf pubescence in autumn ranged from score 0 to score 1. No single morphological trait of a specimen appeared to be sufficient for identification. Even the correspondence between the complex morphological and complex genetic determinations for individuals did not exceed 93% in pure wilds and 64% in hybrids. Genetic variation in pure wild apple is high (species level: P = 90%, A/L = 3.1, He = 0.369). Allelic differentiation & was 0.089, pairwise genetic distance (d0) ranged from 0.065 to 0.148 among five samples. Correspondence between genetic and geographic distance of populations was observed to a certain extent.

Crop-to-wild introgression in the European wild apple Malus sylvestris in Northern Britain

“…A higher threshold can result in the misclassification of hybrids as pure and a lower threshold might have the opposite effect and identify a sample as hybrid when it is actually pure. In previous Malus studies values of P ≤0.1 (Cornille et al, 2013b;Cornille et al, 2015), P ≤0.15 (Larsen et al, 2006) and P ≤0.2 (Coart et al, 2006;Wagner et al, 2014;Feurtey et al, 2017) sylvestris and samples with P dom ≥0.85 and P dom ≥0.80 as pure M. domestica. The threshold for the other classes stayed the same apart from the backcross boundaries being adjusted to reflect the altered threshold for purity.…”

“…Not only has this led to discussions whether genuine wild M. sylvestris still exists today (Henning, 1947;Remmy and Gruber, 1993;Wagner, 1996) but has also raised concerns about the genetic integrity of wild apple. This has recently sparked a number of studies which investigated the extent of hybridisation between the two apple species in Europe using molecular markers (Coart et al, 2003(Coart et al, , 2006Larsen et al, 2006;Schnitzler et al, 2014;Wagner et al, 2014;Cornille et al, 2015;Feurtey et al, 2017). Although results varied between studies the overall picture emerged that hybrids may occur at significant frequencies in wild apple populations (7% to 36%, Cornille et al, 2014).…”

Genomics yields fresh insights on plant domestication

“…“It is now fairly certain that rice evolved in this manner, with Indica rice evolving because of hybridization”, Purugganan explained. “Apples are also a very good example , and we have a paper in review that indicates date palms also benefited from interspecific hybridization”.…”

Origen, dispersión y diversidad del chirimoyo (Annona cherimola Mill.) en el continente americano

“…Son codominantes y su principal desventaja es que están limitados por el bajo número de encimas disponibles y por tanto la resolución de la diversidad es limitada (Mondini et al 2009). Han sido usados desde 1970 para analizar la diversidad genética de plantas (Brown 1978) y, por tanto, también de árboles frutales como muestran algunos trabajos recientes en manzano (Wagner et al 2014), avellano (Leinemann et al 2013) o madroño (Takrouni et al 2012 , Ellegren 2004, Parida et al 2009). Se han propuesto varios modelos de mutación para las secuencias microsatélites como el modelo de alelos infinitos (Infinite Allele Model) (IAM), el de mutación paso a paso (Stepwise Mutation Model) (SMM), o el de formación de un número k de alelos (K-Allele Model) (KAM).…”

“…They are codominant, and their main disadvantage is that the number of available enzymes is limited and, thus, their power to analyze diversity is reduced (Mondini et al 2009). They have been used since the 1970s to analyze genetic diversity in plants (Brown 1978), but they can still provide valuable information for diversity studies in fruit trees shown in some recent works in apple (Wagner et al 2014), hazelnut (Leinemann et al 2013), or Arbutus unedo (Takrouni et al 2012). DNA-based markers, commonly known as molecular markers, have been continuously developed since the 1980s and can be associated or not to a functional trait; they can, in general terms, be classified into dominant (such as RAPDs or AFLPs) or codominant (such as RFLPs, microsatellites, or SNPs) markers depending on whether heterozygous and homozygous genotypes can be distinguished.…”