The Japanese chestnut (Castanea crenata) carries resistance to Phytophthora cinnamomi, the destructive and widespread oomycete causing ink disease. The European chestnut (Castanea sativa), carrying little to no disease resistance, is currently threatened by the presence of the oomycete pathogen in forests, orchards and nurseries. Determining the genetic basis of P. cinnamomi resistance, for further selection of molecular markers and candidate genes, is a prominent issue for implementation of marker assisted selection in the breeding programs for resistance. In this study, the first interspecific genetic linkage map of C. sativa x C. crenataallowed the detection of QTLs for P. cinnamomi resistance. The genetic map was constructed using two independent, control-cross mapping populations. Chestnut populations were genotyped using 452 microsatellite and single nucleotide polymorphism molecular markers derived from the available chestnut transcriptomes. The consensus genetic map spans 498,9 cM and contains 217 markers mapped with an average interval of 2.3 cM. For QTL analyses, the progression rate of P. cinnamomi lesions in excised shoots inoculated was used as the phenotypic metric. Using non-parametric and composite interval mapping approaches, two QTLs were identified for ink disease resistance, distributed in two linkage groups: E and K. The presence of QTLs located in linkage group E regarding P. cinnamomi resistance is consistent with a previous preliminary study developed in American x Chinese chestnut populations, suggesting the presence of common P. cinnamomi defense mechanisms across species. Results presented here extend the genomic resources of Castanea genus providing potential tools to assist the ongoing and future chestnut breeding programs.

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Published in PLOS ONE, v. 12, 9, e0184381, p. 1-13.

This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.

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Authors acknowledge the funding provided by Centro de Estudos Florestais (CEF), which is a research unit funded by Fundação para a Ciência e Tecnologia I.P. (FCT), Portugal (UID/AGR/00239/2013). We acknowledge Fundação para a Ciência e Tecnologia through the project PTDC/AGR-CFL/101707/2008 and the PhD grant SFRH/BD/85140/2012 and also Programa ProDer, Medida 4.1 Refª 45967 “Developing processes and Technologies aiming the production of ink disease resistant. chestnut rootstocks, compatible with national varieties certified with molecular markers” and Programa ProDer, Medida 4.1 Refª 53593 “Innovation in the production chain of chestnut: competitiveness and sustainability”.