Molecular analysis of co-infection of Scots pine seedlings with actinobacteria Streptomyces and Heterobasidion annosum

Heterobasidion annosum is a pathogenic fungus that causes extensive damage to many trees in temperate forests including Scots pine (Pinus Sylvestris). Various microbes have been studied for potential use as bio-control agents to inhibit or reduce the H. annosum infection of trees. This study examined the potential use of bacterial isolates, belonging to streptomyces genus, as a bio-control agent for Scots pine seedlings against H. annosum. Streptomyces species were isolated from surface of mycorrhizal fungi in the forest and they are known to have a mutualistic relationship with mycorrhizal fungi. The goal of this study was to understand the relationship between H. annosum and Streptomyces sp. A11. This was tested in in two settings, in presence of pine seedlings, growing in soil and in dual cultures. In the first setting, seedlings from different treatments were inoculated with Streptomyces sp. A11, H. annosum, co-inoculated with both species or grown in sterile conditions as control. After incubation period, growth and root development of seedlings were analysed. H. annosum grown in dual culture against Streptomyces sp. A11 was utilised for gene expression using quantitative real time PCR method. The results indicated that pine seedlings inoculated with both Streptomyces sp. A11 and H. annosum, had more severe infection compared to the seedlings infected with H. annosum alone. This implies that Streptomyces sp. A11 can interfere with pine’s defence response during interaction with H. annosum. Moreover, Streptomyces sp. A11 suppressed the growth of H. annosum in dual culture. The Suppression of H. annosum was potentially because of antifungal secondary metabolites that were produced by Streptomyces sp. A11. These secondary metabolites caused disruption in glucose metabolism and cell wall integrity of H. annosum. Future experiments should include mycorrhizal fungal species along with species tested in this study. Streptomyces sp. are known to respond differently in presence of specific species. The results for this study should be considered for studies of mycorrhizal associated streptomyces species and can be built upon for broader future investigations