Oomycete communities in lowland tropical forest soils vary in species abundance and comprise saprophytes and pathogens of seeds and seedlings of multiple plant species

Authors: Broders, Kirk; CAPADOR-BARRETO, HERNAN - Smithsonian Tropical Research; Iriarte Broders, Gloria; WRIGHT, S. JOSEPH - Smithsonian Tropical Research; ESPINOSA, HILARIO - Smithsonian Tropical Research; BAUER, MORITZ - Smithsonian Tropical Research; PERALTA, MAYRA ALEJANDRA - Smithsonian Tropical Research; ROJAS, ENITH - Smithsonian Tropical Research; SPEAR, ERIN - Smithsonian Tropical Research

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2024
Publication Date: 11/13/2024
Citation: Broders, K.D., Capador-Barreto, H.D., Iriarte, G., Wright, S.J., Espinosa, H., Bauer, M., Lemus-Peralta, M.A., Rojas, E., Spear, E.R. 2024. Oomycete communities in lowland tropical forest soils vary in species abundance and comprise saprophytes and pathogens of seeds and seedlings of multiple plant species. American Journal of Botany. https://doi.org/10.1002/ajb2.16425.
DOI: https://doi.org/10.1002/ajb2.16425

Interpretive Summary: Soils in tropical forests are full of microbial life which can impact plant diversity through both pathogenic and symbiotic relationships. However, oomycetes which are fungus-like brown algae that produce swimming spores, may have a greater influence on plant diversity because these microbes favor tropical environments with increased precipitation and temperature. An ARS scientist in Peoria, IL, collaborated with scientists at the Smithsonian Tropical Research Institute to assess the diversity and pathogenicity of oomycete species found in a lowland tropical forest in Panama. The study showed that oomycetes are everywhere throughout the Panamanian tropical forest and 2 - 5 time more abundant than oomycetes in U.S. and Mediterranean forests. We identified 24 distinct oomycetes from the soil of which 15 are likely new species. These oomycete species can infect multiple tree species and some species caused greater disease and mortality. These findings demonstrate that oomycetes are widespread pathogens of seeds and seedlings of multiple plant species and have the potential to impact seed and seedling survival in lowland tropical forests. This work will be of interest to foresters, ecologists, plant pathologists and conservationists around the world.

Technical Abstract: The soils in lowland tropics are teeming with microbial life which can impact plant community structure and diversity through plant-soil feedbacks. While bacteria and fungi have been the focus of most studies in the tropics, the oomycetes may have an outsized effect on seed and seedling health and survival, given their affinity for environments with increased precipitation and temperature. Here, we assessed the diversity and pathogenicity of oomycete species present in a lowland tropical forest in Panama using both culture dependent and independent methods to quantify zoospore abundance and species diversity. We found that oomycetes are ubiquitous and common members of the soil microbial community and while less diverse than in temperate forests, they were far more abundant in lowland tropical forests. We also observed variation in oomycete species ability to infect host plants. Species of Pythium were more aggressive, while species of Phytopythium caused less disease but were more diverse and commonly isolated from the soil. Finally, we found that individual hosts accumulate a distinct oomycete community and was the only factor that had an effect community structure. Collectively, these finding demonstrate that oomycetes are ubiquitous, host-generalist pathogens and saprophytes, that have the potential to impact seed and seedling survival in lowland tropical forests.