Secrets of the soil: random or programmed association of benign microbes on plant roots?
Date
2024
Authors
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Publisher
University of Delaware
Abstract
Loss of crops to pests and diseases is an issue that urgently requires our attention, especially in the face of an ever-growing population with mouths to feed. Biocontrols in the form of plant growth promoting rhizobacteria (PGPRs) serve as an alternative to chemical treatments that can persist in the environment and be hazardous to human health. Bacillus subtilis is one form of PGPR found in the soil, that attached to plant roots via communication through secondary metabolites in the soil. This attachment is also important for the activation of induced systemic resistance (ISR) which is one type of plant defense against pathogens like Psuedomonas syringae pv. tomato (PstDC3000). We investigated whether the presence of surfactin or B. subtilis PY79’s ability to produce it impacted its ability to attach to plant roots and subsequently activate ISR. We found that exogenous surfactin in media did appear to increase root attachment. In contrast, a surfactin over producing strain did not trigger root attachment. The addition of the amino acid glutamate (which is crucial for a variety of plant functions) did increase root colonization by both surfactin-null and surfactin producing strains. When placed in abiotic environments in the form of pellicle assays, a surfactin over producing strain formed similar pellicles to those of the undomesticated strain UD1022 whereas PY79 was unable to form complete pellicles. We also noted that when the foliar pathogen PstDC3000 was introduced, root attachment occurred among all three B. subtilis strains regardless of their ability to produce surfactin. However, neither PY79 nor the surfactin over producing strain seemed to decrease the foliar pathogen titers. All the above functions of root attachment or induced systemic resistance (ISR) mediation appear to be surfactin independent. Further studies must be conducted with other secondary metabolites to determine which are important for root attachment and subsequent activation of ISR.
Description
Keywords
Promoting rhizobacteria, Plant roots, Pests, Induced systemic resistance, Root attachment