In agriculture, plant resistance to pathogens is typically short-lived, lasting on the order of a few years. In contrast, resistance in natural plant populations seems to persist for millions of years. Why is resistance ephemeral in agriculture, but seemingly indefinite in natural populations? We address this question by studying the coevolution of natural populations of A. thaliana with natural populations of their pathogens using molecular, genomic and ecological techniques.
Our results led us to a hypothesis about what maintains resistance polymorphisms in natural populations: A. thaliana, unlike plants in agriculture, is rarely challenged with one dominant pathogen. Instead, A. thaliana populations are exposed to thousands of microbes, all at low to intermediate abundances, each with different mechanisms of persistence and/or pathogenicity. A. thaliana seems to evolve resistance in response to this diverse microbial community, and not to one pathogen factor. In short, the heterogeneity of the microbial community selects for heterogeneity in resistance traits.