Verification of wild apple ( <scp> <i>Malus sylvestris</i> </scp> ) nursery stock sold in the United Kingdom

Crop wild relatives are plant taxa that the progenitors of commercial crops and an important genetic resource for improving these making them more resilient in face environmental change. They play role food security it is vital to maintain their natural diversity. However, crop-to-wild gene flow may reduce fitness threaten integrity species long run. Here we investigate purity European apple (Malus sylvestris), a rare tree Europe frequently hybridises with domesticated (M. domestica), sold by UK nurseries. Malus sylvestris (Rosaceae), (or crab) apple, has contributed substantially cultivated genome, domestica (Suckow) Borkh., during domestication history Central Asian progenitor M. sieversii (Ldb.) Roem. (Cornille et al., 2012, 2014). Hybridisation between widely planted been going on time, such hybrid trees now common extent recent studies have raised concerns about (Feurtey 2017; Kišek 2021; Ruhsam 2019; Schnitzler 2014; Wagner Since publication our ongoing research into northern Britain academic specialist literature (Ruhsam Worrell 2017, 2019), as well popular British Wildlife magazine (Worrell 2021), made aware instigation local community-led conservation programs had numerous queries reliable sources pure United Kingdom. Awareness possible negative effects exotic native flora rising (Cordeiro 2020; Novoa 2017), interest activity planting increasing people becoming discerning seed they plant. Commercial nurseries supply practically all stock urban planting, landscape transport infrastructure, farmers general public. Nurseries forestry generally need be Forest Reproductive Material (FRM) registered adhere set industry standards, instance regarding quality provenance (https://www.gov.uk/guidance/marketing-forest-reproductive-material-for-forestry-purposes#frm). It not clear how when sourcing stock, is, able locate or plants entering trade accidentally? For example, Feurtey al. (2017) genotyped 13 seedlings from three nurseries, each located different country (France, Belgium Kingdom). Their results indicated samples companies substantial levels ancestry none could classified pure. Although small numbers this study might reflect wider situation, nevertheless raises questions accurate identification nursery stock. There also anecdotal evidence (2019) majority collected along roads, field borders hedges Scotland were origin. likely many ‘crab’ but actually parentage. syvlestris often alternative pollenisers domestic fruits used historically animal fodder cider, up present jelly (Cox & Beaton, 2002, p. 101). larger intentionally favoured greater productivity. Scottish variety trees, lowlands where common. therefore high frequency hybrids certain areas necessarily sign hybridization events simply reflection mixed origin 2019). Given concern demand Kingdom, aim project was assess We searched internet sites various ordered required minimum amount 12 one supplier November 2019 (Table 1). All came form apart supplier, offered seeds. Upon arrival, potted Royal Botanic Garden Edinburgh. Leaves spring 2020 silica gel DNA extraction. extracted dried leaves using DNeasy Plant kit (Qiagen, Hilden, Germany), following manufacturer's protocol. Before material processed, brown outer layer (testa) seed, which only consists maternal tissue, manually removed under stereomicroscope, leaving white embryo result union paternal gametes assayed 14 microsatellite loci four multiplex reactions (MP1, 2, 3, 4 Cornille (2012), excluding locus CH04e05 MP2 due scoring difficulties) detailed (2019). Numerous shown suitable differentiation sylvestris, 2013, 2015; STRUCTURE v.2.3.4 (Pritchard 2000) admixture 134 plus 104 reference samples, including (nR) newly (nn) (nR = 46), cultivars 26, nn 20, total 46 samples), orientalis 2), hupehensis 3) baccata 5). This software uses Bayesian algorithm infer number distinct groups K data set. The analyses carried out 1–4 100,000 MCMC iterations after burnin 20,000 steps repeated 10 times K, ‘admixture’, ‘correlated allele frequencies’ ‘Separate ? Population’ options selected (see 2019, explanation last option). To identify most dataset, Kfinder (Wang, 2019) calculate parsimony index PI aims populations (K) consistently yield minimal estimates sampled individuals. estimated individual membership coefficients 2000), proportions P identified clusters individual's genomic makeup 2000). A sample if proportion pool PDom ? 0.1 discussion thresholds). output files processed R package ‘pophelper’ (Francis, 2017). Raw scores Dataset S1. compare diversity Excel add-in Genalex v6.501 (Peakall Smouse, 2012) observed (Ho) expected (He) heterozygosity, alleles (Na) effective (Ne). based (total n 238) 3 (Figure consisted group, domestica–M. group (‘Domestica’) containing hupehensis, (‘Orientalis’), consistent distribution surveyed random, cases, particular predominantly origin—either hybrid, domestic, 2). About 31% (4 13, FRM registration) at least 90% analysed two (15%) tested More than 50% (7 53.8%) ‘M. sylvestris’ contained equal (FRM registered) mainly (80%) Remarkably, (N12) 80% 100% its found (n 46) 57) standardised randomly deleting 11 pool. no significant difference heterozygosity Ho (0.734 vs. 0.741, respectively), He (0.750 0.749, Na (9.7 8.6) Ne (4.4 4.5, respectively) (Dataset S3). suggests represented trees. verified markers. Our showed 42.5% (PSyl ? 0.9). (57.5%) either (0.1 0.9), genetically (PDom 0.9) species. clearly customers who supplied wrong species, inadvertently sell potentially serious longer term impacts misidentified wilder places countryside. These introduced outnumber area likelihood being pollinated produce offspring. Misidentification uncommon (Bandelj Javornik, 2007; Lindén Iwarsson, Pinczinger Smith 2007) little those interested buying attractive ornamental garden. misidentification limited (and sometimes difficult identify) same Zaya 53% marketed Celastrus scandens midwestern States invasive C. orbiculatus 64% vendors 11) plants. Another concluded there extensive aquarium genus Myriophyllum, some countries (Thum 2012). In forestry, known problems counterparts hazel (Corylus avellana) cherry (Prunus avium) (Shearer R., 25.3.2022, pers. comm Russel K. 5.4.2022, comm.) woodland creation. obviously agencies mistakenly believe suggested range main reason apparently chain. ‘crab apple’ does exclusively refer (crab) seems any producing fruits. large crab varieties choose from, nothing do obscure parentage (Fiala Daniels, 1994). can daunting task, considering hundreds recognised 1994) even very specialist. If buy wholesale suppliers knowledge, risk getting fruited labelled order distinguish domestica. explain why 5 (38%) background five part imported unknown contrast, (all six originated seeds (?80%) samples. albeit perfect, currently source One among collecting guarantee mother accurately because hard morphological characters Furthermore, still lot fertilising pollen comes pureness depend surrounding donor travel kilometres, half pollination occur within <42 m 75% <101 m. density pure, around crucial importance. Nursery N13, derives (90%) mixture surrounded roughly 50:50 contributions F1 domestica, 75:25 25:75 backcross respectively, sylvestris. Similarly, N2 N6 registered), obtained Additionally, crop vary years depending location tree, happen flower year, chance wind direction pollinator behaviour time. demonstrates collections Currently, seem wholly guaranteed commercially available although (one suggest raise offering provenance. recommend consider paper take appropriate action. undertaking should make efforts carry localities true Seed collectors improve skill identifying nearby potential father trees; far ruling obvious Useful information topics provided (2019), Stace term, establishment orchards stands grown together densities, away best way forward sectors, Work establish type progress Scotland. thank Mary-Ann Smyth providing additional Rodney Shearer Karen Russell comments previous version manuscript. Edinburgh supported Government's Rural Environment Science Analytical Services Division. authors declare conflicts interest. Markus Ruhsam, Rick James Renny jointly created developed procured MR work drafted commented agreed it. Additional supporting findings article supplementary article. microsatellie loc S2. S1 input S3. Genetic Please note: publisher responsible content functionality authors. Any (other missing content) directed corresponding author