Burkholderia contaminans siderophore-rich supernatants suppress post-harvest anthracnose in avocado fruits

Abstract Siderophores are iron-chelating secondary metabolites that can effectively control fungal diseases in several agronomically important crops. In the present study, the bacterium Burkholderia contaminans MSR2 was found to profusely accumulate siderophores when grown under iron-limiting conditions. Therefore, subsequent experimental procedures were performed to determine whether the siderophore-rich supernatants of B. contaminans MSR2 were effective against anthracnose disease caused by Colletotrichum gloeosporioides in post-harvest avocado fruits. Dual culture assays performed in vitro showed that B. contaminans MSR2 produced an approximate 25% reduction in the radial mycelial growth of C. gloeosporioides. Moreover, cell-free supernatants (CFSs) with a siderophore concentration of 58.08 mM deferoxamine mesylate equivalent caused a 78% reduction of C. gloeosporioides growth under in vitro conditions. In avocado fruits, siderophore-rich CFSs significantly reduced the severity and incidence of post-harvest anthracnose disease, similar to the effect produced by the Captan 4L fungicide (2-(trichloromethylsulfanyl)-3a,4,7,7a-tetrahydroisoindole-1,3-dione) at 2 g/L. Untargeted metabolomic analyses of B. contaminans CFSs obtained under iron-limited conditions revealed the predominant accumulation of the ornibactin C8 and pyochelin siderophores, in addition to numerous other antimicrobial compounds, including secondary siderophores and further biological compounds known to have fungitoxic activity. These results support the proposal that siderophore-rich bioactive CFSs from B. contaminans MSR2 can be effectively employed for biological control of post-harvest anthracnose in avocado fruits. Key points • B. contaminans MSR2 cell-free supernatants (CFSs) inhibited C. gloeosporioides’growth. • CFSs and Captan similarly reduced post-harvest anthracnose damage in avocado fruits. • Pyochelin, pyochelin-like, ornibactin C8, and tetrapeptide siderophores were prominent anti-anthracnose CFSs.