Genetic relationships and hybrid vigour in olive (Olea europaea L.) by microsatellites I RIS B ITON 1 ,S OFIA S HEVTSOV 1 ,O REN O STERSETZER 1 ,Y AIR M ANI 1 ,S HIMON L AVEE 1,2 , B ENJAMIN A VIDAN 1 and G IORA B EN -A RI 1, 3 1 Institute of Plant Science, Volcani Center, ARO, P.O. box 6, Bet-Dagan, 50250, Israel; 2 The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 76100, Israel; 3 Corresponding author, E-mail: giora@agri.gov.il With 3 figures and 4 tables Received December 10, 2011/Accepted July 20, 2012 Communicated by J. Léon Abstract The olive (Olea europaea) is one of the most important oleaginous crops of the Mediterranean basin. Increased demand for olive oil creates a need for new olive varieties to help meet the requirements of the global market. However, olive breeding has been handicapped by such varied challenges as a prolonged juvenile period, agrotechnical problems and insufficient genetic knowledge. The use of DNA markers has the potential to over- come these problems and increase the effectiveness of classical breeding programmes. In this study, co-dominant polymorphic simple sequence repeats (SSRs) were used as markers to analyse the genetic relationships between several local and other ‘non-native’ olive cultivars. Cluster analy- sis revealed four major groups among the 15 cultivars examined in this study. Table and oil cultivars were clustered in different groups. However, the clusters did not differentiate between cultivars of different geographi- cal origins. In addition, we used the data gathered to analyse genetic rela- tionships to evaluate the effects of heterosis in agricultural traits. Genetic distances between cultivars were determined based on the SSR genotype data and were used for evaluating the possible effects of heterosis in vari- ous F 1 populations. Interestingly, phenotypic data of F 1 progenies from crosses between different cultivars indicated the potential effects of hetero- sis as expressed in several traits. Genetic distance between parents was significantly correlated to F 1 performance for three traits: percentage of dry fruit weight, oil content and commercial oil production. Thus, crosses between olive cultivars exhibiting relatively extensive genetic distances one from the other are expected to result in better progeny performance in future Olea breeding programmes. Our study linked assessment of biodi- versity of commercial olive cultivars with the application of this informa- tion in olive breeding programmes for selection of specific parents to generate superior new cultivars. Key words: microsatellites — olive — breeding programme — heterosis The olive (Olea europaea L.), which is native to the eastern Mediterranean region, has been commercially cultivated in the Mediterranean basin for about 6000 years and has since spread to many other parts of the world. The olive is a predominantly allogamous species showing a high degree of out-crossing, which has resulted in considerable levels of heterozygosity and DNA polymorphism among individuals (Angiolillo et al. 1999, Rallo et al. 2000). Different strategies have been employed to evaluate the genetic diversity among different olive cultivars, including morphological, agronomical and biochemical character- izations. The introduction of DNA markers in past decades has provided a valuable discriminatory system, independent of envi- ronmental conditions. Recent advances in plant genomics may point the way to linking genes and specific traits and thereby lead to more efficient and predictable breeding programmes. DNA markers can be applied in a variety of ways, such as DNA fingerprinting, genetic screening and chromosome mapping. DNA markers have been used in plant breeding programmes for various purposes in addition to their role in the identification of genes of interest and the development of marker assisted selection. These applications include identification of individual plants and plant populations, assessment of genetic distances (phylogeny), identifi- cation of parental lines for the production of hybrid seeds and a significant decrease in the number of backcross generations needed to achieve gene introgression. The major applications of DNA markers for the improvement of classical breeding projects include conserving the genetic diversity of parental stocks, selecting suit- able parents for the generation of heterosis, decreasing the number of backcross generations in gene introgression projects and pyram- iding various genes in the same cultivar. In olives, DNA markers have been used in the characterization of germplasm collections, in breeding programmes, in paternity testing and cultivar traceability (Bracci et al. 2011), by restriction fragment length polymorphism (Besnard and Berville 2002), ran- dom amplified polymorphic DNA (RAPD) (Wiesman et al. 1998, Bronzini de Caraffa et al. 2002, Martins-Lopes et al. 2008, Awan et al. 2011), amplified fragment length polymorphism (Angiolillo et al. 1999, Baldoni et al. 2006, Albertini et al. 2011), single- nucleotide polymorphism (Macedo et al. 2009, Muleo et al. 2009) and others (Busconi et al. 2006, Besnard et al. 2007). More recently, SSRs have proven to be suitable markers for cultivar identification in olives, because they are transferable, highly polymorphic and co-dominant (Rallo et al. 2000, Carriero et al. 2002, Cipriani et al. 2002, Beghe et al. 2011, Corrado et al. 2011, Ercisli et al. 2011, Rotondi et al. 2011). Almost all olive-producing countries have recently implemented active olive breeding programmes with the aim of establishing new olive cultivars that are more suitable for the modern olive oil industry (Lavee 1990). Conventional breeding techniques, which include clonal and varietal selection, as well as induced mutagene- sis, are still widely used for the improvement of olive cultivars (Panelli et al. 1990, Lavee and Avidan 2000). The establishment of olive cultivar collections and the efforts being made to diversify olive germplasm in many olive-growing countries have encour- aged genetic studies on the molecular level and their application in wileyonlinelibrary.com Plant Breeding doi:10.1111/pbr.12001 © 2012 Blackwell Verlag GmbH