Resumen
The massive mortality of Castanea sativa in southwestern Europe, which was caused by different species of Phytophthora spp., led to the introduction of seeds of the Asiatic species Castanea crenata and Castanea mollissima and to hybridization to breed for resistance to Phytophthora spp. In Spain, two programmes were developed: one programme, focussed mainly on obtaining first generation hybrids by controlled pollinations, and the other programme, based on selection among open-pollinated progenies collected from first and second generation hybrids, in both cases between sweet and Japanese chestnut. A clone collection of 194 of the clones obtained is conserved at the Lourizán Forest Reseach Centre, and 32 of these were approved as basic material for forest reproduction. A sample of 356 individuals was genotyped using 13 isozyme loci, including the clone collection and several stands of Asiatic species. Only three loci were identified as being diagnostic among these species. The diversity of stands of both Asiatic species was reduced compared to that of C. sativa. Genotype inspection of diagnostic loci and two Bayesian procedures (STRUCTURE and NEWHYBRIDS) were used to classify all individuals into genealogical classes and, thus, reconstruct the history of chestnut hybridization in Spain.