RT Journal Article T1 Selecting cork oak and holm oak trees for stable tolerance to combined drought and Phytophthora cinnamomi stress A1 Mata Pombo, Raul de la A1 Alcaide Romero, Francisco A1 González González, Rubén A1 Cuenca Valera, Beatriz A1 Tapias Martín, Raúl A1 Pérez Martín, Felipe A1 Solla Hach, Alejandro AB Using trees tolerant to drought and Phytophthora cinnamomi (Pc) infection is the most promising approach to restore Quercus suber and Q. ilex forests under decline. Breeding programs require heritability estimates for tolerance to combined stress. Moreover, the genetic variation underlying genotype-by-environment (G × E) interactions in oak tolerance to combined stress has not been explored. We evaluated life expectancy of approximately 10,400 seedlings from 87 Q. suber and 90 Q. ilex half-sib families from Spain under Pc, Pc + drought, and drought + Pc scenarios. Intraspecific variation in tolerance across scenarios, additive genetic variance, and G × E interactions were analyzed. To ensure optimal selection strategies, family genotypic stability was quantified. Under well-watered conditions, Q. suber showed higher tolerance than Q. ilex to Pc, but under the Pc + drought scenario, mortality was similar between species. Geographic variation was detected in cork oak, with populations from eastern Spain showing greater susceptibility. Both species exhibited significant additive genetic variation under the Pc and Pc + drought scenarios, and narrow-sense heritability estimates (hi2) ranged from 0.10 to 0.16, indicating potential for selective breeding. We report a relevant G × E interaction, primarily due to family rank changes across scenarios. Genotypic stability analyses enabled selection of families with increased and stable tolerance, and the Pc + drought scenario was deemed optimal for selection. A backward selection strategy targeting the 20% most tolerant parents would allow genetic gains of 18% in both oak species. This is the first time oaks have been screened for enhanced and stable tolerance to combined stress. PB Springer SN 1612-4669 SN 1612-4677 (electrónico) YR 2026 FD 2026 LK https://hdl.handle.net/10272/27985 UL https://hdl.handle.net/10272/27985 LA eng NO Mata, R.de la, Alcaide, F., González, R., Cuenca, B., Tapias, R., Pérez, F., & Solla, A. (2026). Selecting cork oak and holm oak trees for stable tolerance to combined drought and Phytophthora cinnamomi stress. European Journal of Forest Research, 145(2). https://doi.org/10.1007/s10342-025-01857-3 NO Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. Junta de Extremadura, 2352999ER003, 2352999ER003, 2352999ER003, Fundación Española para la Ciencia y la Tecnología,RTA2014-00063-C04-04, RTA2014-00063-C04-04, RTA2014-00063-C04-04, RTA2014-00063-C04-04 DS Repositorio Institucional de la Universidad de Huelva RD 30 may 2026