Dataset of the publication: Selecting cork oak and holm oak trees for stable tolerance to combined drought and Phytophthora cinnamomi stress

To explore patterns of inter- and intra-specific variation in tolerance to different scenarios of drought and Phytophthora cinnamomi (Pc) infection combinations, acorns were collected from nine Quercus suber and nine Q. ilex populations across their natural distribution in Spain. The cork oak populations were from nine different provenance regions and the holm oak populations were from eight.In fall 2019, acorns were collected from seven to 11 (average of 10) open-pollinated, asymptomatic and unrelated mature wild mother trees per population. Collected seeds were divided into three batches and sent to the three locations where the experiment was conducted . Each batch was handled and sown in mid-January 2020, following the same protocol. The experiment was conducted in three greenhouses in Maceda (NW Spain), Huelva (SW Spain) and Plasencia (W Spain). In Maceda, open pollinated seeds from 87 Q. suber and 90 Q. ilex mother trees (half-sib families) were arranged in a randomized complete block design replicated in 42 blocks. In each block, the two species were intermixed and one seed per family (177 seeds/block) was placed at random. Each root trainer comprised 48 cells, such that four root trainers were required to complete one block. In Huelva and Plasencia, seeds from a subsample of 70 Q. suber and 73 Q. ilex mother trees were arranged in a randomized complete block design replicated in 19 and 21 blocks respectively. Again, species were intermixed and one seed per family (143 seeds/block) was placed at random. Thus, three 48-cell root trainers were needed to complete one block. The total number of emerged seedlings was 6,072 in Maceda, 2,120 in Huelva and 2,139 in Plasencia. In each greenhouse, seedlings were subjected to a different treatment of drought and Pc infection combination. A single stress scenario of Pc was applied in Maceda. On 2 July 2020, seedlings in Maceda were soil infested with a highly virulent Pc strain. After inoculation, trays were flooded for three days to promote sporangia production and zoospore release, and inoculated plants were waterlogged three more times in summer to stimulate the effect of Pc. Apart from the four waterlogging periods, seedlings were periodically watered to field capacity to avoid drought stress. The same treatment was applied again in the following growing season. A combined Pc+drought scenario was applied in Plasencia. On 2 July 2020, seedlings were soil infested with Pc and trays were flooded for three days after inoculation. Trays were waterlogged three times in summer and watered to field capacity only once a month until the end of October. This treatment simulated a typical dry summer scenario. The same treatment was applied again in the following growing season. A combined drought+Pc scenario was implemented in Huelva. On 1 June 2020, irrigation was stopped for one month at this location, simulating a typical dry spring. On 2 July 2020, seedlings were soil infested with Pc. Trays were flooded for three days after inoculation and waterlogged three times in summer, following the same protocol as for the Pc scenario. The same treatment was applied again in the following growing season. Seedlings were kept under natural light and optimal growing conditions, and therefore no other source of mortality was expected. The experiment lasted two growing seasons and ended on 20 November 2021.