The Janzen-Connell hypothesis proposes the interactions between plants and host-specific natural enemies especially fungal pathogens, explained the coexistence of the enormous number of tree species. However, knowledge of the obligate pathogen along with its host plant and the host specific infection mechanism remains limited. In this study, we investigated the host specificity of root-associated fungi of different plant species in a subtropical monsoon forest south China. We collected 113 entire root systems from four different plant species. For each root individual, we cultured single fungi colony on PDA media. Then we identified the fungal strains and verified their pathogenic effect in a series of inoculation experiments. To evaluate the host specificity of these pathogenic strains, we performed bioassays with six fungi and inoculated to conspecific seedlings as well as other four heterospecific seedlings. Finally, we investigated the host specificity infection mechanism by different plant species infected with GFP-labeled fungal pathogens and this result would provide visualized evidence of host specificity.
Results/Conclusions
In growth-room inoculation experiment, we found six fungi, which isolated from roots and identified by ITS sequencing, had strong pathogenicity on their host seedlings. Host specificity test showed that five isolated fungi had lethal effect on their own seedlings, but caused none or less effect on other four species. Moreover, green fluorescent protein (GFP) was transformed and expressed in four fungi in order to monitor the interaction between pathogens and plants. The inoculation result demonstrated visualized differences in pathogenic mechanism among different hosts. In conclusion, our work provides strong evidences for host specificity of the pathogen and reveals its infection mechanism in subtropical forest.