GENETIC DIVERSITY OF MEDLAR (MESPILUS GERMANICA) GERMPLASM USING MICROSATELLITE MARKERS

Abstract

The medlar (Mespilus germanica) is a pome fruit related to pear (Pyrus sp.) and hawthorn (Crataegus sp.) that has been cultivated for many centuries for its edible fruit. It was also an important medicinal plant in the Middle Ages. The center of origin for Mespilus is the Trans-Caucasus region and traditional uses for the fruit extend through the Middle East, Central Asia and western Europe. The Mespilus collection at the USDA National Clonal Germplasm Repository (NCGR) at Corvallis, Oregon, USA, includes 60 seed and plant accessions with origins in 10 countries. Several ancient cultivars with different names and sources have indistinguishable phenotypes and synonymy has long been suspected. Twenty-one simple sequence repeat (SSR) markers from apple and two from pear were tested for polymorphism in eleven medlar accessions. Nine apple SSRs were polymorphic in medlar. Five easy-to-score SSRs from apple were used to genotype 41 clones of M. germanica and one accession of the intergeneric hybrid species M. canescens growing at the NCGR. Seven very large fruited clones with five different countries of origin were genetically indistinguishable from ‘Monstreuse d’Evreinoff’. Four clones from western Oregon sources with similar phenotypes also produced identical SSR profiles. Two other pairs of synonyms were also documented. One of the five SSRs (NZ05g8) distinguished ‘Marron’ and ‘Macrocarpa’ from the ancient English cultivar ‘Nottingham’. Flow cytometry confirmed M. canescens as triploid and showed all M. germanica accessions to be diploid. The relationships determined in this study document the diverse genetic backgrounds represented in the NCGR medlar collection. These results also will permit the removal of unnecessary duplication and improve the efficient management of this collection.