Abstract
The genus Lysobacter includes several bacterial species which show potential for being used in biological control of plant diseases. It was shown recently that several Lysobacter type strains produce volatile organic compounds (VOCs) which controlled the growth of Phytophthora infestans in vitro when the bacteria were grown on a protein rich medium. In the present study, Lysobacter capsici AZ78 (AZ78) has been tested for its potential to produce VOCs that may contribute to the bioactivity against soilborne plant pathogens. To this end, split Petri dish assays of bacterial cultures have been combined with GC-MS measurements with the aim to reveal the identity of the VOCs which inhibit the growth of Pythium ultimum Rhizoctonia solani, and Sclerotinia minor. While AZ78 completely suppressed the growth of P. ultimum and S. minor, the growth of R. solani was still reduced significantly. The GC-MS analysis revealed 22 VOCs to be produced by AZ78, the majority of which were (putatively) identified as mono- and dialkylated methoxypyrazines. Based on additional cultivation and GC-MS experiments, 2,5-dimethylpyrazine, 2-ethyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine were selected as presumable bioactive compounds. Further bioassays employing indirect exposure to standard solutions (1–10 mg per Petri dish) of the synthetic compounds via the gas phase, revealed that each of these pyrazines was able to suppress the growth of the pathogens under investigation. The results of this study highlight the possible future implementation of pyrazine derivatives in the control of soilborne plant diseases and further support the biocontrol potential of L. capsici AZ78.
Highlights
The recent years, the scientific community is increasingly questioning the use of synthetic chemical pesticides in plant disease management, as their impact on human health and the environment are coming to surface (Alavanja et al, 2004; Köhler and Triebskorn, 2013)
At 96 hpi, all three soilborne plant pathogens covered the total surface of the PDA growth medium when grown in absence of L. capsici AZ78 in split Petri dishes
P. ultimum and S. minor mycelium development was totally inhibited as no growth was observed (Figure 1), while Rhizoctonia solani growth was significantly inhibited by AZ78 volatile organic compounds (VOCs), compared to the control (Figure 1)
Summary
The recent years, the scientific community is increasingly questioning the use of synthetic chemical pesticides in plant disease management, as their impact on human health and the environment are coming to surface (Alavanja et al, 2004; Köhler and Triebskorn, 2013). Microbial volatile organic compounds (VOCs) have come into the limelight as potential candidates to substitute the outlawed chemical fumigants (De Boer et al, 2019) Their physiochemical characteristics such as low boiling point, high vapor pressure and low molecular weight (
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