The forest in a changing climate: identifying mildew-resistant oaks and using them for forest regeneration
A white coating on the upper side of the leaves reveals mildew, which mainly affects young oaks and deprives them of vital nutrients. This makes the fungal disease a challenge for forest regeneration measures. In the joint project "MetaEiche", researchers from the Technical University of Kaiserslautern (TUK) are now working with the Research Institute of Forest Ecology and Forestry (FAWF) in Trippstadt to investigate how resistant oaks can be specifically selected. The Forest Climate Fund of the Federal Ministry of Food and Agriculture (BMEL) and the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) is funding the project with around 500,000 euros.
The native oak species English oak(Quercus robur) and sessile oak(Quercus petraea) characterize the face of German mixed forests. "Throughout Germany, they make up around 10 percent of the tree population; in Rhineland-Palatinate, they even account for a good 20 percent," explains Prof. Dr. Matthias Hahn from the TUK's Biology department. "Oaks are among the most valuable forest trees, both because of the high quality of the wood and because of the great biological diversity of organisms that live in oak habitats. In addition, oaks are better able to adapt to climate change than other forest trees due to their resistance to drought. It is therefore a long-term goal of forestry to increase the proportion of oaks."
Dr. Stefan Seegmüller, Hahn's project partner, is investigating a natural method of forest regeneration at the FAWF in Trippstadt, which takes the form of light cone felling. "We open up the canopy of forest stands, which are often dominated by beech as the oak's biggest competitor, in small areas just enough to allow enough light to reach the ground for regrowing trees. The oaks remain standing and can drop their fruit on the exposed areas. Vital young oaks prevail over the equally upwardly striving beeches with the help of fast-growing shoots. However, if the young leaves and shoot tips are infested with mildew, they lose the competition. That's why it's important for a climate-stable forest that we promote mildew-resistant oaks."
In recent years, Seegmüller has planted oak seedlings of various origins in a wooded area near Trippstadt. These are transferred to climate chambers and then tested by TUK biologists for their susceptibility to mildew using a specially developed infection method. The scientists are looking for defense mechanisms that are anchored in the trees' genetic material. "We often observe clear differences in the infestation of directly neighboring trees or young plants," says Hahn. "These differences are apparently based, at least in part, on heritable traits that give some trees partial resistance to mildew. A key aim of the project is to clearly demonstrate and utilize these genetically determined resistance mechanisms in order to be able to select the vital and less susceptible individuals when regenerating oak stands."
The final goal of the project partners is to decipher the infection process of the powdery mildew fungus and the defense reactions of the oak seedlings in detail. On this basis, the researchers want to develop a quick and reliable test to determine the powdery mildew defense potential of the plants for silvicultural practice - initially in climate chambers in the laboratory and subsequently on demonstration plots in the forest.
The "MetaEiche" project is also thematically linked to another research project currently being financed by the Forest Climate Fund to promote oaks: The 'Survivor Oaks' project, which is being led by researchers at the Thünen Institute of Forest Genetics near Hamburg and the Helmholz Center in Munich, is primarily aimed at selecting and growing oaks that are particularly resistant to insects and drought. "Due to the overlaps between the two projects, we have agreed to cooperate and will support each other," adds Hahn.
Questions answered:
Prof. Dr. Matthias Hahn
Department of Biology at the TU Kaiserslautern
Tel.: 0631 205-2402
Email: hahn@biologie.uni-kl.de
Infection mechanisms, fungicide resistance and genetic diversity of Botrytis cinerea and related Botrytis spp.
Our research focuses on the grey mould fungus, Botrytis cinerea, a major pathogen of more than 200 fruits, vegetables, ornamental flowers and other crop plants. By using molecular genetic, cytological and genomic/ transcriptomic approaches, we are studying the molecular tools that enable B. cinerea and related Botrytis spp. to colonize their host plants. Another focus is the investigation of fungicide resistance mechanisms and the problem of massive fungicide resistance development of B. cinerea in agricultural environments.
1. infection mechanisms of Botrytis cinerea and the role of the phytotoxic secretome
Botrytis cinerea attacks hundreds of mostly dicotyledonous plant species, causing serious pre- and postharvest losses in fruits, vegetables, ornamental flowers and other crop plants. As a necrotrophic pathogen, B. cinerea rapidly kills the host cells and colonizes the dead host cells. Several components have been identified that contribute to infection, including the phytotoxins botrydial and botcinin (Dalmais et al., 2011), cell wall degrading enzymes (Kars et al., 2005; Nafisi et al., 2014), and various phytotoxic proteins (Arenas et al., 2010; Noda et al., 2010; Zhang et al., 2015; Gonzalez et al., 2017; Zhu et al., 2017). B. cinerea induces cell death by triggering the plant hypersensitive response, thus exploiting a host defense mechanism for infection (Govrin & Levine, 2000). However, different plant suicide pathways exist, which differently promote resistance and susceptibility to necrotrophic fungi (Lai et al., 2011; Kabbage et al., 2013), and it is still unclear how B. cinerea overcomes the suicide- associated host defenses. Secretion of oxalic acid (OA) and host tissue acidification have been suggested to contribute to virulence of B. cinerea (Prusky et al., 2013). A recent investigation of an oahA mutant lacking did not clearly support a role of OA in acidification and infection (Müller et al., 2018). As described above, the secretome of B. cinerea contains a mixture of phytotoxic components, however, none of them alone has proven to be critical for the infection process. We therefore assume that B. cinerea has adopted a host killing strategy involving the release of a redundant mixture of phytotoxic metabolites and proteins. In order to assess the relative importance of each of these components, a comprehensive approach involving sequential ablation of the phytotoxic potential, as well as determining the role of each individual component is required. We are currently developing improved strategies for mutagenesis of B. cinerea, including optimizing the simultaneous use of different resistance markers for selection, and CRISPR-Cas-based methods that enable the generation of multiple mutants and the introduction of site-specific changes in the B. cinerea genome.