Francisco J. Ruiz Gómez reports on the Spanish oaks breeding programme.
Holm oak and cork oak are the most representative trees of the Iberian Peninsula. These two species cover more than half of the forest territory of Spain, spanning 3.4 million hectares across Spain and Portugal. For decades, their sustainability has been compromised by forest decline, with severe episodes of tree mortality linked to root rot, threatening the environmental and socioeconomic stability of key rural areas in the southwest of the peninsula.
In response to this challenge, the Spanish Ministry for the Ecological Transition and the Demographic Challenge developed a programme for the preservation and plant breeding of cork and holm oaks in the face of oak decline. In 2017, the General State Administration promoted a coordinated group for the inventory and management of the decline, as well as the genetic breeding of the two main affected species. This initiative led to the establishment in 2019 of the “Programa Nacional de Mejora y Conservación de la Encina y el Alcornoque frente al Síndrome de la seca”, which involves 15 different institutions, including state and regional government bodies, public universities, and public research organizations.
The programme, coordinated by TRAGSA (Empresa Pública de Transformación Agraria, S.A., S.M.E.), completed its first phase between 2019 and 2024 with significant advances. Among these, the programme identified and characterized tolerance to Phytophthora cinnamomi and drought stress in both species, and developed the techniques and protocols necessary to provide forest reproductive material tolerant to “La seca” for afforestation purposes. Among the main activities accomplished, extensive fieldwork was conducted, characterizing more than 350 trees across 53 disease foci located in the regions of Andalucía, Extremadura, and Castilla-La Mancha. Furthermore, large-scale trials for tolerance assessment were conducted on the progeny of the selected trees, micropropagation protocols were tested for both species, the relationship between the microbiome, disease impact, and tolerance was studied using high-throughput sequencing techniques, and breeding populations, source material plantations, and in-field tolerance experiments were established.
Last year, a second phase of the programme was launched, aiming to continue this ambitious initiative with the following objectives: i) to complete the number of components for the seed orchards (breeding plantations for the production of acorns); ii) to create a national database of genetic materials of holm and cork oak for conservation purposes; iii) to continue advancing the development of clonal propagation techniques for both species and to standardize these protocols; and iv) to promote technical and scientific knowledge regarding the management of these two species and the decline syndrome affecting them.
The activities related to the first and second objectives have been carried out during 2025 and the spring of 2026. In these tasks, the TRAGSA group and the University of Córdoba (UCO), with the support of the Universities of Extremadura and Huelva, have located and characterized the additional parentals required. The researchers from UCO, who are members of the OAK-HOPE consortium, are in charge of several activities, including a task of ex-situ conservation focused on the development of grafting techniques, the microbiome characterization, and the identification and characterization of putatively tolerant parentals in Andalucía. During recent months, fieldwork has been completed, with 360 additional trees identified in disease foci. In this second phase, most of these were cork oak individuals, completing the selection in areas where the first phase failed to collect reproductive material due to decline status and climatic conditions.
This year, for the first time in the last decade, acorn production in the cork oak forests of Andalucía has been excellent, allowing the collection of genetic material from a relevant part of Los Alcornocales Natural Park and the peripheral population of Huelva, which belongs to provenance region 7 (RP7).
In the coming years, the programme aims to approve and register the basic materials for the production of forest reproductive material (seed orchards and mixtures of clones), including the publication of the molecular profiles of the clones for their identification, and continue advancing knowledge regarding the dieback syndrome to halt its spread, as it causes invaluable ecological impact and millions in economic losses in rural areas of the southwestern Iberian Peninsula. This is an excellent example of how collaborative research and coordinated efforts—including public administration, technicians, academia, and researchers—can deliver applied solutions to solve complex challenges within the framework of environmental management.
Acknowledgements: To all members of the working group on breeding of Mediterranean Quercus, for their dedication, collaboration, and valuable contributions throughout this project.