Cell-free supernatants from plant growth - promoting rhizobacteria Bacillus albus strains control Aspergillus flavus disease in peanut and maize seedlings

Abstract

Background: Aspergillus flavus, a seed-borne fungal pathogen, can colonize host plants and exploit nutrients, hindering the growth of seedlings such as peanut and maize. This study investigated the effectiveness of cell-free supernatants (CFSs) from plant growth - promoting rhizobacteria (PGPR) Bacillus albus NNK24 and NDP61 in suppressing the growth of A. flavus AF1. Results: The antifungal activity of these CFSs was attributed to their surfactant properties and chemical profile, characterized through rapid chemical assays and UHPLC-ESI-QTOF/MS combined with bioinformatic analysis using GNPS and npatlas. Identified putative antifungal compounds included two diketopiperazines (cyclo(pro-leu) and cyclo(2-hydroxy-Pro-R-Leu)), four macrolactins (7-O-succinyl macrolactin A, 7-O-methyl-5'-hydroxy-3'-heptenoate-macrolactin, macrolactin C, and macrolactin B), two siderophores (bacillibactin and petrobactin), and three lipopeptides (kurstakin 1, 2 or 3, and 4). Both CFSs exhibited strong suppression of the harmful effects of A. flavus AF1 and seed-borne A. flavus on peanut and maize seedlings, as evidenced by significantly reduced Disease Incidence (DI) and Disease Severity Index (DSI) compared to the control. The Disease Control Efficacy (DCE) of CFS treatments was equivalent to that of commercial fungicide treatments. Additionally, all CFS treatments stimulated seed germination, vigor, seedling length, and weight in both peanut and maize, with Vigor Index (VI) values increasing by 222.4%–286% and 181.7%–216.4% relative to the negative control for peanut and maize seedlings at 7 days after treatment (DAT), respectively. Conclusion: These results suggest that the CFSs of PGPR B. albusNNK24 and NDP61 hold promise as effective bioprotection agents in sustainable agriculture.