Pythium oligandrum is an Oomycete. It is a parasite of many fungi and other oomycetes including Botrytis, Fusarium and Phytophthora. It has been licensed as a biocontrol agent in the form of an oospore soil treatment, which reduces pathogen load and concomitant plant disease.
P. oligandrum can grow within the roots of certain plants, including tomato and sugar beet. Production of auxin-like substances stimulate plant growth. Defense responses can be induced in the plant, which primes the plant from further infection by pathogenic fungi, oomycetes or bacteria.
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Le Floch,G., Rey,P., Benizri,E., Benhamou,N. and Tirilly,Y. (2003) Impact of auxin-compounds produced by the antagonistic fungus Pythium oligandrum or the minor pathogen Pythium group F on plant growth. Plant Soil, 257, 459-470.