SSR diversity and hybridization of wild apples (Malus spp.) growing in the Guadarrama and Ayllón mountain ranges (Central Spain)

Abstract

Aim of study: The crab apple tree (Malus sylvestris (L.) Mill.) is a wild crop relative of the apple tree (M. domestica Borkh.). Hybridization and genetic exchange between these species has been studied in some European regions, but there is no record in Spain. This work aimed to characterise a set of 330 feral and crab apples. Area of study: Guadarrama and Ayllón mountain ranges (Central Spain). Material and methods: We used 12 microsatellites to detect intermediate profiles. To do so, diversity, multivariate and population structure Bayesian analyses were performed on the sample, adding a total of 28 crab apples, feral and widespread apples varieties as references. Main results: We found a large molecular diversity in this Malus germplasm, scoring a mean of 28.58 alleles per locus (A); an observed heterozygosity (Ho) of 0.80 and a very low value of inbreeding coefficient (Fis =0.06). On the other hand, we found from our Bayesian population analysis three populations (one per species and a third one very admixed) apparently not spatially correlated and a substantial level of intermediate genetic profiles, as around 47% of the feral trees and 35% of crab apples may be hybrids. Research highlights: Connectivity in the crab apple genetic pool is still functional and interspecific gene flow may be relevant. Nevertheless, further conservation measures and research must be carried to understand the population dynamics between both species.