ISSR analysis of cultivars of pear and suitability of molecular markers for clone discrimination

Inter-simple sequence repeat (ISSR) markers were used for cultivar identification and for determination of the phenetic relationships among 24 pear cultivars (Pyrus communis L.). The ability of several molecular marker systems including randomly amplified polymorphic DNA (RAPD), amplified fragment length polymorphisms (AFLP), inter-simple sequence repeats (ISSR), simple sequence repeats (SSR), and selective amplification of microsatellite polymorphic loci (SAMPL) to detect variation among clones of the most significant Portuguese cultivar, Rocha, was also investigated. Each of the eight ISSR primers tested was able to distinguish the 24 pear cultivars. The ISSR primers generated 337 markers, 79.5% of which were polymorphic. The cultivar dendrogram obtained with the ISSR marker data was very similar to that obtained with previous RAPD+AFLP analysis, confirming the genetic divergence of 'Perola','Carvalhal' and 'Lawson' from the other cultivars. Eight out of 15 apple [Malus sylvestris (L.) Mill. var domestica (Borkh.) Mansf.] SSR primers tested also amplified microsatellites in pear. None of the five molecular marker systems analyzed (with a total of 1082 markers) detected reproducible polymorphisms among the nine 'Rocha' clones, in spite of the presence of clear phenotypic differences.