Inhibitory Effects of Linear Lipopeptides From a Marine Bacillus subtilis on the Wheat Blast Fungus Magnaporthe oryzae Triticum

Abstract

Wheat blast is a devastating fungal disease caused by a filamentous fungus, Magnaporthe oryzae Triticum (MoT) pathotype, which poses a serious threat to food security of South America and South Asia. In the course of screening novel bioactive secondary metabolites, we found that some secondary metabolites from a marine Bacillus subtilis strain 109GGC020 remarkably inhibited the growth of M. oryzae Triticum in vitro at 20 µg/disk. We tested a number of natural compounds derived from microorganisms and plants and found that five recently discovered linear noncytotoxic lipopeptides, gageopeptides A-D (1-4) and gageotetrin B (5) from the strain 109GGC020 inhibited the growth of MoT mycelia in a dose-dependent manner. Among the five compounds studied, gageotetrin B (5) displayed the highest mycelial growth inhibition of MoT followed by gageopeptide C (3), gageopeptide D (4), gageopeptide A (1), and gageopeptide B (2) with minimum inhibitory concentrations (MICs) of 1.5, 2.5, 2.5, 10.0, and 10.0 µg/disk, respectively. Application of these natural compounds has also completely blocked formation of conidia in the MoT fungal mycelia in the agar medium. Further bioassay revealed that these compounds (1-5) inhibited the germination of MoT conidia and, if germinated, induced deformation of germ tube and/or abnormal appressoria. Interestingly, application of these linear lipopeptides (1-5) significantly suppressed wheat blast disease on detached wheat leaves. This is the first report of the inhibition of mycelial growth, conidiogenesis, conidial germination, and morphological alterations in the germinated conidia and suppression of wheat blast disease by linear lipopeptides from the strain of B. subtilis. A further study is needed to evaluate the mode of action of these natural compounds for considering them as biopesticides for managing this notorious cereal killer.

Wheat blast: a new threat to food security

“…Application of these natural compounds have also completely blocked formation of conidia in the MoT fungal mycelia in the agar medium. Further bioassay revealed that these natural compounds inhibited the germination of MoT conidia, and even if conidia germinated, induced deformation of germ tube and/or abnormal appressoria occurred (Chakraborty et al 2020). Application of these linear lipopeptides significantly suppressed wheat blast disease on detached wheat leaves.…”

“…Genomic and laboratory analyses revealed that these bacteria suppressed wheat blast fungus through antibiosis and induced systemic resistance in the wheat plants. Recently, Chakraborty et al (2020) demonstrated that some non-cytotoxic linear lipopeptide isolated from a marine Bacillus subtilis strain 109GGC020 inhibited asexual development (inhibited conidiogenesis and germination of conidia) of the MoT fungus both in vitro and in vivo. Among the 5 compounds identified, gageotetrin B displayed the highest mycelial growth inhibition of MoT followed by gageopeptide C, gageopeptide D, gageopeptide A and gageopeptide B with minimum inhibitory concentrations (MICs) of 1.5, 2.5, 2.5, 10.0 and 10.0 μg/disk, respectively.…”

“…These biocontrol agents may be worth testing for the management of wheat blast. Discovery of novel antagonistic plant probiotic (beneficial bacteria associated with plant) bacteria from the local environment including wheat and their metabolites could be an alternative option to less-effective fungicides for the management of the wheat blast (Surovy et al 2017;Dutta et al 2018;Chakraborty et al 2020).…”

Oligomycins Inhibit Magnaporthe oryzae Triticum and suppress wheat blast disease

“…Therefore, pyriform conidia developed from conidiophores and conidia germination with appressorial development at the germ tube tips are essential steps of the disease cycle of MoT [16]. Disrupting any of these asexual life stages reduces the chance of pathogenesis [21]. Finding of natural bioactive compounds inhibiting any of these phases of asexual life is considered to be the first step in the production of a new fungicide for MoT .…”

“…So far, no report has been demonstrated on the antagonistic impacts of Streptomyces spp., and/or their secondary metabolites to control wheat blast disease. We screened 150 natural compounds belonging to the class alkaloids, terpenoids, macrolides, macrotetrolides, tepenoids, and phenolics isolated from different plants and microorganisms on mycelial growth and asexual development of wheat blast fungus MoT in our laboratory [21]. Among them, two macrolides, oligomycin B and oligomycin F, previously extracted from the marine Streptomyces spp.…”