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Intracellular plant defense against pathogens is mediated by a class of disease resistance genes known as NB‐LRRs or NLRs (R genes). Many of the diseases these genes protect against are more prevalent in regions of higher rainfall, which provide better growth conditions for the pathogens. As such, we expect a higher selective pressure for the maintenance and proliferation of R genes in plants adapted to wetter conditions. In this study, we enriched libraries for R genes using RenSeq from baits primarily developed from the common sunflower (Helianthus annuus) reference genome. We sequenced the R gene libraries of Silphium integrifolium Michx, a perennial relative of sunflower, from 12 prairie remnants across a rainfall gradient in the Central Plains of the United States, with both Illumina short‐read (n = 99) and PacBio long‐read (n = 10) approaches. We found a positive relationship between the mean effective annual precipitation of a plant's source prairie remnant and the number of R genes in its genome, consistent with intensity of plant pathogen coevolution increasing with precipitation. We show that RenSeq can be applied to the study of ecological hypotheses in non‐model relatives of model organisms. [ABSTRACT FROM AUTHOR]

Empirical evidence of the influence of climate on plant–pathogen coevolution is limited but crucial to understand, as anthropogenic pressures including fragmentation and climate change threaten biodiversity. In this study, we tested patterns of plant–pathogen coevolution using Silphium integrifolium Michx., a native tallgrass prairie species that is undergoing domestication, and its foliar pathogens. We collected seeds from four native prairie remnants from each of three regions along an east–west precipitation gradient in central North America and used these to create three common gardens in each region. In common gardens and remnant prairie populations, we measured symptoms of foliar disease (leaf rust and leaf blotch, both caused by fungal pathogens, and Silphium clear vein (SCV), which we have evidence is associated with a virus). While we did not observe greater disease in the East common garden, we did find that on average the East populations had greater resistance to disease than West populations, consistent with an evolutionary legacy of more rapid coevolution with high precipitation. We also found strong interactions between source region and region of planting for all diseases. The Silphium rust, caused by the specialist pathogen Puccinia silphii, was better able to infect plant populations from the same region. These patterns are consistent with local adaptation of specialist pathogens to their local hosts as expected from Red Queen dynamics. For the generalist fungal pathogen driving leaf blotch, we did not observe evidence of local adaptation. However, we observed a positive correlation in the average level of leaf blotch symptoms observed in individual populations in common gardens with the levels of disease in the S. integrifolium individuals in the prairie remnants of origin, consistent with S. integrifolium genetics determining symptoms in the field. Our results are consistent with pathogen ecology being a major driver of coevolutionary dynamics along productivity gradients. As S. integrifolium is being domesticated for oilseed production, our results identify distinct targets for resistance alleles in breeding efforts and can guide pathogen management strategies. [ABSTRACT FROM AUTHOR]

Ongoing domestication of whole‐leaf rosinweed, Silphium integrifolium Michx., as a perennial oilseed and forage crop aims to increase yields while limiting decreases in other desirable traits (i.e., trade‐offs). Two changes to plant architecture, increasing pistillate ray florets head−1 (= feminization) and reduced lateral branching of stems, have been considered for their potential to improve oil yields but with limited understanding of potential trade‐offs. Field tests with genets that vary for feminization failed to show that increasing the number of female florets head−1 had any effect on pollinator visitation and seed set (%) but revealed that feminization reduced embryo mass achene−1. In general, tripling the number of ray florets head−1 reduced the mass of individual embryos by 50% or more, which suggests feminization still provides a net benefit for oil yields. Clipping (bud removal) used to simulate reduced branching in S. integrifolium affected components of yield in ways that were generally predictable; heads (receptacles) became larger and mass achene−1 increased. However, the large number of buds removed to achieve modest increases in head size and achene mass make reduced branching appear undesirable. Ultimately, S. integrifolium genets with genetically reduced branching are needed to make the best evaluation of this potential change. Both sets of experiments reveal plasticity in S. integrifolium yield components and suggest that efforts to improve the quality of phenotypic data are important to efficient selection. Core Ideas: Silphium integrifolium genets with ≈30–90 female florets head−1 did not vary in seed set (%).Genets with more female florets had lighter embryos, but still improved yields head−1.Bud removal used to simulate reduced branching increased mass achene−1 by almost one‐third.The number of buds removed to increase achene mass makes reduced branching appear undesirable.Achene mass (or embryo mass) and receptacle diameter are plastic traits in S. integrifolium. [ABSTRACT FROM AUTHOR]