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Genetic structure of Spanish pea landrace collection using ISSR markers

Landraces or traditional varieties are local populations, maintained and multiplied by farmers. They are simultaneously adapted to local environmental conditions through the process of natural selection, and continuously selected for desirable traits (Zeven, 1998). Their dissemination is not necessarily limited to a particular region, and successful landraces are propagated across natural and political borders through seed exchange and trade. However, increased seed exchange can put the adaptation of landraces at risk (Parzies et al., 2004) Therefore, identification of patterns of adaptation and magnitude of seed exchange traceable in genebank collections are of the crucial importance for developing of appropriate conservation strategy. The Spanish pea landraces collection is conserved in CRF-INIA and ITACyL includes 439 accessions collected in Spain, in a wide geographic area of different ecological conditions. Information of accessions within collection includes passport and characterization data (available at www.inia.es). A subset of 289 accessions (250 of them are analyzed in this contribution) has been also characterized by means of ISSR markers by using 10 ISSR which have produced a total of 112 polymorphic bands. The number of bands per primer ranges from 7 to 15. For measuring inter-populational diversity, DNA was extracted and amplified following the methodology previously published. The diversity of the Spanish landraces has been previously studied by different authors (Lázaro & Aguinagalde, 2006 ; Martín-Sanz et al., 2011). Classification of accessions based on molecular data was carried out by both excluding spatial information (to detect genetic stratification independent of geographic distribution) and including it (to detect assumptive pattern of regionalization). The extent of seed exchange was investigated by a correlogram between geographic distance and genetic coancestry. Both Bayesian model-based clustering (STRUCTURE, Pritchard et al., 2000) and distance-based clustering (UPGMA on Jaccard’s distance matrix) detected two distinct clusters. Neither of inferred clusters was confined to a specific geographic region nor related to any of environmental covariates. Furthermore, spatial model-based clustering using TESS (Durand et al., 2009) failed to detect any spatial cluster of accessions. A correlogram based on geographic distance classes and pairwise kinship coefficients indicates that seed exchange was practically unlimited throughout Spain, because only the most distant accessions were detected to be less related than random.

pea; landrace collection; geentic variability

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