Microevolution of fungal plant parasites by means of adaptation to host and climate - a case study using the Acacia rust genus Ravenelia

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Most of the major crop diseases are caused by fungal plant parasites like rice blast fungus, coffee rust or soybean rust. However, besides their destructive effects in agriculture, in more natural ecosystems they are supposed to play important roles in maintaining genetic diversity of their host plants. Host-parasite interactions are among the most studied systems in terms of molecular analysis of the underlying genetic interactions between the two partners. But still, the evolution of host-parasite interactions is only poorly understood. The strong host specificity of some fungi like the rust or smut fungi have been discussed as a result of close coevolution, but so far it seems that several competing theories can explain these observed patterns of host-parasite distribution with similar support and an all-embracing explanation is lacking. While many studies have focused on the long-term effects of coevolution in terms of parallel evolution, the a better understanding of the differential effects of biotic (host genotype) and abiotic factors (e.g. climatic conditions) in shaping the evolutionary outcome of a host-parasite interaction is urgently needed. Thus, in the proposed project we aim to disentangle the influence of host specificity and climate on the microevolution of an Acacia-rust in South Africa using a population genetics approach. The rust fungus Ravenelia macowaniana infects two distinct tree species of the genus Vachellia (Acacia s.l.) distributed in two different climatic regions in South Africa, where both habitats are linked by transition in two isolated localities. A circular sampling design spanning both host species in their major distribution ranges will allow us to separate the different effects on the population level.We will use low coverage genome sequencing of four specimens of Ravenelia macowaniana collected on both host species in distinct regions to develop highly variable microsatellite markers for a population genetic analysis. Based on a dense sampling of 24 populations in total we want to analyse whether the host or the environment exert the higher impact on a plant pathogens genotype. The experimental setup of separated as well as overlapping populations of host tree species in contrasting environments is designed to allow an interpretation with respect to both scenarios, separately and combined. Thus, our project will provide basic information on the evolution of host specific plant parasites in a natural environment. This will allow understanding microevolutionary processes like speciation, host shifts and coevolution much better and our results could serve as a model for agriculture and forestry as well.