Epiphytic fungi induced pathogen resistance of invasive plant against .

Background: (L.) Sweet is a destructive invasive weed in South China but rarely infected with pathogens in nature. Its pathogen resistance mechanism is largely unknown at present. Some non-pathogenic isolates of and are prevalent on many plant species and function as pathogen resistance inducers of host plants. The objective of the present research is to investigate whether the symbiosis between the both fungi and is present, and thereby induces pathogen resistance of

Methods: Through field investigation, we explored the occurrence rates of and on leaf surfaces of plants in natural habitats and compared their abundance between healthy leaves and leaves infected with , a natural pathogen. With artificial inoculation, we assessed their pathogenicity to and studied their contribution of pathogen resistance to against

Results: We found that and were widely epiphytic on healthy leaf surfaces of in sunny non-saline shady non-saline and sunny saline habitats. Their occurrence rates reached up to 100%. Moreover, we found that the abundance of and on leaves infected with were significantly lower than that of healthy leaves. With artificial inoculation, we empirically confirmed that and were non-pathogenic to . It was interesting that colonization by , alone and a mixture of both fungi resulted in a reduction of infection to accompanied by lower lesion area to leaf surface area ratio, increased hydrogen peroxide (HO) concentration and salicylic acid (SA) level relative to the control. However, expression, chitinase and β-1,3-glucanase activities as well as stem length and biomass of plant only could be significantly improved by and a mixture of both fungi but not by . In addition, as compared to colonization by and a mixture of both fungi, induced significantly higher jasmonic acid (JA) level but significantly lower β-1,3-glucanase activity in leaves of plants. Thus, our findings indicated the symbiosis of epiphytic fungi and induced systemic resistance of against . played a dominant role in inducing pathogen resistance of . Its presence alleviated the antagonism of the JA signaling on SA-dependent β-1,3-glucanase activity and enabled plants to maintain relatively higher level of resistance against