Antifungal volatiles from macrobasidiomycetes inhibits Fusarium oxysporum f.sp. lycopersici

Several macrobasidiomycete fungi have potential biological properties naturally to combat fungal diseases. F.oxysporum f.sp. lycopersici is a soilborne ascomycetous fungus, which causes disease in several vegetable crops. The present study aimed to explore the antifungal activity of VOCs produced by several macrobasidiomycete fungi against F. oxysporum f.sp. lycopersici. The VOCs emitted by macrobasidiomycete fungi were demonstrated by the inverted sealed plate assay against the target pathogen. Among the mushroom isolate tested in vitro, the VOCs exhibited from Coprinus cinereus inhibited 70 % mycelial growth of F. oxysporum f.sp. lycopersici, followed by Ganoderma lucidum (60.28 %) and Lentinus edodes (35.28 %). In addition to inhibition of the pathogen, the headspace volatiles emitted by the effective isolate were trapped by Tenax column and subjected to GC-MS analysis. A total of 15 and 25 VOCs were identified from C. cinereus and G. lucidum, respectively. Among them, Alfa copaene showed a peak area percentage of 7.82 (14.99 RT) in Coprinus cinereus. followed by 2 undecanone. Similarly, trichloromethane and 1- pentanol produced from G. lucidum, showed high relative abundance of 71.5 per cent at 9.84 RT and 70.3 per cent at 2.69 RT, respectively. The VOCs produced by macrobasidiomycete fungi could possess antimicrobial activities against the fungal pathogen. These volatile compounds may be explored as a novel biocontrol agent against soil borne pathogens of vegetable crop.

Microbiota Associated with Sclerotia of Soilborne Fungal Pathogens – A Novel Source of Biocontrol Agents Producing Bioactive Volatiles

Soilborne plant pathogens are an increasing problem in modern agriculture, and their ability to survive long periods in soil as persistent sclerotia makes control and treatment particularly challenging. To develop new control strategies, we explored bacteria associated with sclerotia of Sclerotinia sclerotiorum and Rhizoctonia solani, two soilborne fungi causing high yield losses. We combined different methodological approaches to get insights into the indigenous microbiota of sclerotia, to compare it to bacterial communities of the surrounding environment, and to identify novel biocontrol agents and antifungal volatiles. Analysis of 16S rRNA gene fragment amplicons revealed significant compositional differences in the bacterial microbiomes of Rhizoctonia sclerotia, the unaffected tuber surface and surrounding soil. Moreover, distinctive bacterial lineages were associated with specific sample types. Flavobacteriaceae and Caulobacteraceae were primarily found in unaffected areas, while Phyllobacteriaceae and Bradyrhizobiaceae were associated with sclerotia of R. solani. In parallel, we studied a strain collection isolated from sclerotia of the pathogens for emission of bioactive volatile compounds. Isolates of Bacillus, Pseudomonas, and Buttiauxella exhibited high antagonistic activity toward both soilborne pathogens and were shown to produce novel, not yet described volatiles. Differential imaging showed that volatiles emitted by the antagonists altered the melanized sclerotia surface of S. sclerotiorum. Interestingly, combinations of bacterial antagonists increased inhibition of mycelial growth up to 60% when compared with single isolates. Our study showed that fungal survival structures are associated with a specific microbiome, which is also a reservoir for new biocontrol agents.

Caryolan-1-ol, an antifungal volatile produced by Streptomyces spp., inhibits the endomembrane system of fungi

Streptomyces spp. have the ability to produce a wide variety of secondary metabolites that interact with the environment. This study aimed to discover antifungal volatiles from the genus Streptomyces and to determine the mechanisms of inhibition. Volatiles identified from Streptomyces spp. included three major terpenes, geosmin, caryolan-1-ol and an unknown sesquiterpene. antiSMASH and KEGG predicted that the volatile terpene synthase gene clusters occur in the Streptomyces genome. Growth inhibition was observed when fungi were exposed to the volatiles. Biological activity of caryolan-1-ol has previously not been investigated. Fungal growth was inhibited in a dose-dependent manner by a mixture of the main volatiles, caryolan-1-ol and the unknown sesquiterpene, from Streptomyces sp. S4–7. Furthermore, synthesized caryolan-1-ol showed similar antifungal activity. Results of chemical-genomics profiling assays showed that caryolan-1-ol affected the endomembrane system by disrupting sphingolipid synthesis and normal vesicle trafficking in the fungi.