Identification and Functional Verification of Differences in Phenolic Compounds Between Resistant and Susceptible Populus Species.

Poplar canker, mainly caused by Botryosphaeria species, is a serious disease that has resulted in the reduced productivity and death of poplar worldwide. Different Populus species have varied resistance levels to poplar canker; however, whether phenolic compounds in poplar are involved in this resistance remains uncertain. Here, we determined the concentrations of phenolic compounds and their antifungal activities in canker-resistant P. tomentosa and canker-susceptible P. beijingensis. We identified 29 phenolic compounds with significantly different concentrations between the two species. Salicylic acid (SA), tremuloidin, salicin, and poplin were dominant in P. tomentosa, while benzoic acid (BA) and catechol were dominant in P. beijingensis. These six phenolic compounds were further tested for antifungal activities. SA, BA, and catechol showed significant antifungal activities against Botryosphaeria dothidea, while the other three compounds showed no activity. As BA or catechol can be converted in plants to SA, which is a remote signaling molecule that plays an important role in plant defenses, we presumed that the resistance of P. tomentosa was initiated by SA, while the susceptibility of P. beijingensis resulted from the absence of SA. Further studies are required to confirm this hypothesis. These results provide a foundation for future research on the disease-resistance mechanisms of poplar.