Geographic and genetic variation in susceptibility of Butomus umbellatus to foliar fungal pathogens

Authors: HARMS, NATHAN - Us Army Corp Of Engineers (USACE); SHEARER, JUDY - Us Army Corp Of Engineers (USACE); CRONIN, JAMES - Louisana State University; Gaskin, John

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2019
Publication Date: 10/16/2019
Citation: Harms, N., Shearer, J., Cronin, J., Gaskin, J.F. 2019. Geographic and genetic variation in susceptibility of Butomus umbellatus to foliar fungal pathogens. Biological Invasions. https://doi.org/10.1007/s10530-019-02109-3.
DOI: https://doi.org/10.1007/s10530-019-02109-3

Interpretive Summary: Flowering rush (Butomus umbellatus) is an aquatic invasive plant in the U.S. We tested whether the common genotypes differed in disease attack or if different diseases were in different parts of the US. Genotype 1 plants had a lower disease incidence than Gentoype 4 plants in the field (38% vs 70%) but similar fungal richness. Despite these field results, our bioassays revealed that Genotype 1 plants consistently received a higher damage score and produced larger leaf lesions regardless of pathogen used. These results demonstrate that the two widespread B. umbellatus lineages have differential susceptibility to the pathogens and that potential pathogen biological controls may be more effective against G1 plants.

Technical Abstract: Large-scale patterns of plant invasion may reflect regional heterogeneity in biotic (plant competition or natural enemy attack) and abiotic (climate) factors, and genetic variation within and between invading populations. Having information on how patterns of biotic resistance vary spatially can be especially important when implementing a biological control program because introduced agents may have differential impacts through interactions with host-genotype, local environment, or other novel enemies. We conducted a series of field surveys and greenhouse/laboratory studies to determine whether there was evidence of biotic resistance, in the form of foliar fungal pathogens, in two common introduced lineages (triploid G1, diploid G4) of the Eurasian wetland weed, Butomus umbellatus in the U.S. We tested whether lineages differed in disease attack and whether spatial patterns in disease incidence related to geographic location or climate emerged for either lineage. First, we surveyed 27 populations (17 G1 populations, 10 G4 populations) across the US distribution of B. umbellatus to document the proportion of plants with disease symptoms and pathogen species associated with these plants. For a subset of plant populations, we isolated and cultured pathogenic foliar fungi and then tested pathogenicity, ability of the fungi to cause disease, of three different isolates in laboratory (excised-leaf) assays. After accounting for location (latitude, climate), G1 plants had a lower disease incidence than G4 plants in the field (38% vs 70%) but similar fungal richness. Despite these field results, our bioassays revealed that G1 plants consistently received a higher damage score and produced larger leaf lesions regardless of pathogen used. The seemingly contradictory results between pathogen incidence in the field and pathogeneticity in the laboratory/greenhouse may be due to differential susceptibility during B. umbellatus development stages or climatic differences between areas that limit the regional pool of pathogen taxa or their effect on plant lineage. These results demonstrate that the two widespread B. umbellatus lineages have differential susceptibility to the pathogens and that potential pathogen biological controls may be more effective against G1 plants.