Pseudomonas fulva HARBPS9.1: candidate anti-Fusarium agent in South Africa

Phytopathogens causing mycotoxicoses in maize are a potential threat to grain quality and availability in many maize producing countries including South Africa. The use of natural biological agents for controlling maize fusariosis and many other such plant diseases, as opposed to the more traditional use of chemicals, is growing in popularity globally, as a greater emphasis gets placed on public health. In this study, nine Fusarium inhibiting isolates representing a subset of 200 native Pseudomonas isolates from the maize rhizosphere of 10 different farms in the North West Province of South Africa were further evaluated for their in vitro biocontrol potential. Although few of the isolates (PS1.1, PS1.22, PS2.2, PS6.4, PS6.8, PS7.2, PS8.3, PS8.6, and PS9.1) had impressive in vitro biosuppressive effects against Fusarium graminearum and Fusarium culmorum, while also producing biosurfactants, only isolate HARBPS9.1 showed consistent antifungal capacity along with maize seed bioprotection capability. The candidate antagonist HARBPS9.1 was molecularly characterized as a Pseudomonas fulva strain and was found to harbor multiple functional biosynthetic gene clusters after FTIR, NMR and ESI-Q-TOF-MS metabolomics investigation. P. fulva HARBPS9.1 bioprotective mechanism is attributed to the possible presence of hydrogen cyanide, pyrrolnitrin, and rhamnolipids.