Characterization of the Genetic Diversity Among Cultivated Pears Using SSR Markers

Pear species (Pyrus spp.) is one of the most commercially important fruit tree species in the subfamily Maloideae of the Rosaceae. P. communis (European pear) is commonly cultivated in Europe and temperate regions, while P. pyrifolia is the main cultivated pear species in Asia. Registration of new cultivars either for Plant Breeders Rights or National Listing purposes requires Distinctiveness Uniformity and Stability test to be completed. DUS tests are based on the comparison between candidate cultivars and accessions of the reference collection. Developing new efficient tools to help to manage reference collections is a great concern.

The mains aims of the present study were to characterize the reference collection of pear using SSR markers, and to define a highly discriminating marker set.

Study has been carried out on leaves of 142 pear accessions (P. communis, P. pyrifolia, and P. calleyryana) collected from INRA ex situ collection, including 7 references genotypes recommended by ECPGR. Samples were genotyped with 37 SSR markers publicly available and evenly distributed throughout the genome.

On the 37 SSR markers, 6 were discarded due to weak amplification. The 31 remaining SSR markers were efficient to separate European and Asian pears and identify uniquely 111 accessions. Among the varieties with similar molecular profile, 19 were cultivars and its mutants. Nevertheless for 6 pairs of varieties with a genetic distance equal to 0 (concerning 12 accessions) further analysis are needed. A reduced set of markers was defined with an equivalent discriminatory power compared to the complete set of markers.

In conclusion, the set of 31 SSR markers and the reduced set could be used to establish strategies to manage the reference collection and provide true-to-type analysis.