Lunes, 14 Enero 2019 12:00

Drought determines Holm oak defense strategies Destacado

Research at the University of Cordoba underscores the importance of water stress on the response of Holm oaks facing Phytophthora infection

Holm oak decline is threatening the sustainability of the dehesas, making it one of the most worrisome problems in the field of forest health for the scientific community. Depsite considering the pathogen Phytophthora cinnamomi the main trigger for this situation, external conditions, such as extreme drought, are also determining factors in the process of dying woodland. 

In the context of global change, the dehesa is not only threatened by pests and diseases, but also drought and extreme rainfall are becoming some of the main disturbances that will have to be faced in the future. To this end, a group of researchers from the Departament of Forest Engineering at the University of Cordoba made up of Francisco Ruiz, Alejandro Pérez de Luque, Rafael Sánchez, José Luis Quero and Rafael M. Navarro, have been studying the different physiological responses of Holm oaks when dealing solely with this pathogen versus when doing so under the condition of water stress. 

Holm oaks infected with Phytophthora cinnamomi growing in conditions without water stress (optimal watering), respond to the pathogen physiologically with strategies of reducing biomass and reallocating resources. That is to say, as a defense mechanism, the plant with infected roots activates its secondary metabolism and stops its growth, but other parameters, such as photosynthetic efficiency, are not affected. Thanks to these mechanisms, this group of plants was able to cope with the disease, and in doing so, avoid irreversible root damage and recover after the first cycle of infection. 

However, the response is drastically different when the infection comes on top of water stress due to drought. In this case, photosynthesis decreases and the plant is unable to respond to the infection, and even die from it. In this way, the study demonstrates the influence of water stress as a trigger for Holm oak decline that when added to the pathogen, exemplifies the worst case scenario for dehesa oak groves.

The most innovative aspect of this study is the combined assessment of the physiological and growth responses in plants under biotic and abiotic water stress, considering the issues derived from the Holm oak’s natural variability. By using only one population in the study, and seedlings from the same parental tree, the variability in the response is reduced, thus strengthening the study’s results.

As extreme drought is becoming more and more common in Andalusia, the results of this research indicate that not only must the pathogen be dealt with but that managing strategies must be incorporated in order to stop the pathogen from spreading and to reduce the impact of climate change and severe droughts upon Holm oaks, by improving its own defense mechanisms when facing root rot.

Ruiz Gómez, FJ; Pérez-de-Luque, A; Sánchez-Cuesta, R; Quero, JL; Navarro-Cerrillo, RM (2018) Differences in the Response to Acute Drought and Phytophthora cinnamomi Rands Infection in Quercus ilex L. Seedlings. Forests, 9, 634; doi:10.3390/f9100634


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