Susceptibility to Phytophthora cinnamomi of six holm oak (Quercus ilex) provenances: are results under controlled vs. natural conditions consistent?

Aim of study: Quercus forests are being affected by severe decline and mortality. The oak decline is associated with the soilborne pathogen Phytophthora cinnamomi (Pc), among others. This work aims to determine if Quercus ilex growing in Pc-infested soils show mortality differences according to their provenance in the field. It also evaluates whether the most tolerant provenances are those with the greatest constitutive chemical defences. Area of study: Acorns from six Spanish National Parks with natural presence of Q. ilex were collected for sowing in the greenhouse and later be planted on soils naturally infested by Pc in the surroundings of Plasencia, western Spain. Materials and methods: Seedlings were planted in four field plots located in two areas with oak decline: 153, 156, 157 and 155 plants in plot I, II, III and IV, respectively. The presence and infection of Pc was confirmed before their installation and during the experiment. Symptoms, regrowth, mortality and development was recorded for four years. Main results: There was a high mortality (56.0-80.5%) with differences among provenances. The most tolerant provenances in the field coincided with those identified under greenhouse conditions in a previous test. Provenances with higher constitutive condensed tannins better tolerate the pathogen under both conditions. In the southern provenances, some families with higher tolerance and, therefore, candidates for use in reforestation programs in areas infected by Pc, were identified. Research highlights: The restoration of Pc-affected areas would be possible through the use of Q. ilex plant material with high constitutive defences, more tolerant to the pathogen.