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Disease protection and allelopathic interactions of seed-transmitted endophytic pseudomonads of invasive reed grass (Phragmites australis)

White, JamesF., Kingsley, KathrynI., Kowalski, KurtP., Irizarry, Ivelisse, Micci, April, Soares, MarcosA., Bergen, MarshallS.
Plant and soil 2018 v.422 no.1-2 pp. 195-208
Phragmites australis, Poa annua, Pseudomonas fluorescens, Rumex crispus, Taraxacum, allelopathy, bacteria, biodiversity, branching, damping off, disease resistance, endophytes, haplotypes, invasive species, mortality, pathogens, root meristems, seed germination, seedling growth, seedlings, seeds, soil
BACKGROUND AND AIMS: Non-native Phragmites australis (haplotype M) is an invasive grass that decreases biodiversity and produces dense stands. We hypothesized that seeds of Phragmites carry microbes that improve seedling growth, defend against pathogens and maximize capacity of seedlings to compete with other plants. METHODS: We isolated bacteria from seeds of Phragmites, then evaluated representatives for their capacities to become intracellular in root cells, and their effects on: 1.) germination rates and seedling growth, 2.) susceptibility to damping-off disease, and 3.) mortality and growth of competitor plant seedlings (dandelion (Taraxacum officionale F. H. Wigg) and curly dock (Rumex crispus L.)). RESULTS: Ten strains (of 23 total) were identified and characterized; seven were identified as Pseudomonas spp. Strains Sandy LB4 (Pseudomonas fluorescens) and West 9 (Pseudomonas sp.) entered root meristems and became intracellular. These bacteria improved seed germination in Phragmites and increased seedling root branching in Poa annua. They increased plant growth and protected plants from damping off disease. Sandy LB4 increased mortality and reduced growth rates in seedlings of dandelion and curly dock. CONCLUSIONS: Phragmites plants associate with endophytes to increase growth and disease resistance, and release bacteria into the soil to create an environment that is favorable to their seedlings and less favorable to competitor plants.