Abstract
Pythium oligandrum is a unique biological control agent. This soil oomycete not only acts as a mycoparasite, but also interacts with plant roots and stimulates plant defense response via specific elicitors. In addition, P. oligandrum can synthetize auxin precursors and stimulate plant growth. We analyzed the secretomes and biochemical properties of eleven Pythium isolates to find a novel and effective strain with advantageous features for plants. Our results showed that even closely related P. oligandrum isolates significantly differ in the content of compounds secreted into the medium, and that all strains secrete proteins, amino acids, tryptamine, phenolics, and hydrolytic enzymes capable of degrading cell walls (endo-β-1,3-glucanase, chitinase, and cellulase), exoglycosidases (especially β-glucosidase), proteases, and phosphatases. The most different strain was identified as a not yet described Pythium species. The changes in metabolism of Brassica napus plants grown from seeds coated with the tested Pythium spp. were characterized. Enhanced levels of jasmonates, ethylene precursor, and salicylic acid may indicate better resistance to a wide variety of pathogens. Glucosinolates, as defense compounds against insects and herbivores, were enhanced in young plants. Altogether, P. oligandrum strains varied in their life strategies, and either they could perform equally as plant growth promoters and mycoparasites or they had developed one of these strategies better.
Highlights
Biological control agents (BCAs) represent a promising, environmentally friendly approach to protecting plants against a vast array of pathogens
As Pythium oligandrum is well-known for its beneficial features, we searched for other Pythium oomycetes with high potential for use as BCAs
The mycoparasitism tests of the M1 strain as an example are shown in the Supplementary Materials (Figures S1–S4)
Summary
Biological control agents (BCAs) represent a promising, environmentally friendly approach to protecting plants against a vast array of pathogens. These agents include fungi, oomycetes, and bacteria, and their positive effect stems from interactions that prime defense responses and enhance plant resistance to future stressors [1]. A striking number of soilborne diseases of various plants can be controlled by Pythium oligandrum, including ascomycetes, basidiomycetes, and pathogenic oomycetes [3]. P. oligandrum is a nonpathogenic soil inhabitant with worldwide distribution, which belongs to the class of filamentous eukaryotic microorganisms (oomycetes) and stands out among promising licensed biological agents. P. oligandrum has numerous beneficial effects on plant fitness, which result from the synergistic action of direct and indirect mechanisms on plant protection. P. oligandrum competes for nutrients and/or space with its target organisms
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