The continuous cropping obstacles inmonoculture fields are a major production constraint for peanuts.Application of the endophytic fungus Phomopsis liquidambarihas increased peanut yields.Further studieshave found that nodulation and N2fixation increasesfollowingP.liquidambari infection were important factors for improving peanut yield.However,the mechanisms involved in this process remain unknown.This work showed that compared with only Bradyrhizobium inoculation,co-inoculation with P.liquidambari significantly elevated endogenous H2O2 and NO levels in peanut roots.Pre-treatment of seedlings with specific scavengers of H2O2 and NO blocked P.liquidambari-induced peanut nodulation and N2fixation.H2O2 scavenger not onlysuppressed the P.liquidambari-induced nodulation and N2fixation but also enhanced H2O2 and NO generation.Nevertheless,the NO scavenger did not significantly inhibit the induced H2O2 biosynthesis,implying that H2O2 acted upstream of NO production.These results were confirmed by observations that exogenous H2O2 and NO reversed the inhibition of P.liquidambari-increased peanut nodulation and N2fixation.The transcriptional activities of the symbiosis-related genes SymRK and CCaMK also increased significantly in response toP.liquidambari,H2O2 and NO treatments.The pot experiment further confirmed that the P.liquidambari infection-enhanced H2O2 and NO signalling pathways were significantly related to the increase in peanut nodulation and N2fixation.This is the first report that P.liquidambari acts as an endophytic elicitor to increase peanut-Bradyrhizobium interactions via enhanced H2O2/NO-dependent signalling crosstalk,which is conductive to the alleviation of continuous cropping obstacles via an increase in nodulation and N2 fixation.