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.
Pine wilt disease is a devastating forest disease worldwide caused by the pinewood nematode (PWN; Bursaphelenchus xylophilus). Esteya vermicola is widely recognized as a promising bio‐control agent effective against PWN. During a survey of associated microorganisms of Pinus yunnanensis in Southwest China, a novel isolate of E. vermicola was obtained. This isolate produced two types of conidia. One type of conidia was hyaline, unicellular, bacilloid, and non‐adhesive. The second type of conidia is solitary, hyaline, unicellular asymmetric elliptic or lunate, concave inward, ending slightly apiculate, adhesive on the concave surface, and contained an ovoid endospore‐like structure. Only the lunate conidia showed infection activity against PWN. This novel isolate produced a high proportion of infective lunate conidia and exhibited high adhesion and infection activity against PWN by adhering to the nematode within 48 h and killing 74.5% of the tested PWN individuals within 4 days. Given that the isolate was obtained from P. yunnanensis, it may be well adapted to the endogenous environment of pine trees. The isolate shows potential as a bio‐control agent against a plant‐parasitic nematode in the field.
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