Chemical Ecology of Rathayibacter toxicus and Associated Bacteria: Profiling Volatile Compounds for Insights into Annual Ryegrass Toxicity Causative Agent

The study involved the isolation of bacteria from the surface of Rathayibacter toxicus infested ryegrass seeds, followed by an analysis of volatile organic compounds (VOCs) to identify biomarkers associated with each bacterial species. Among the four isolated bacteria (a species of Pantoea, two species of Pseudomonas and R. toxicus ), three were evaluated for their antibiosis potential against R. toxicus. The main objective of this research was to characterize the volatile compounds produced by R. toxicus and to assess the capability of the other three bacteria to serve as biological control agents. The volatile chemicals were identified by using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC–MS) in the aforementioned bacterial species. The identified compounds such as 1-nonanol, geraniol, decanoic acid and 2-decanone may serve as biomarkers for R. toxicus. Additionally, obtained information on VOCs may facilitate chemical communication between bacteria and the nematode which is responsible to carry it to the ryegrass plant. During the antibiosis assay, Pantoea agglomerans and Pseudomonas cedrina, among the endophytic/epiphytic bacterial species, produced compounds that significantly inhibited R. toxicus growth in vitro, with capacity values 22.7 ± 2.3 and 20.0 ± 2.0, respectively. In conclusion, this study's findings have significant implications for the management of annual ryegrass toxicity (ARGT), as they highlight the promising potential of P. agglomerans and Ps. cedrina as viable candidates for biological control strategies in ARGT management.