Investigation on the mechanisms of wilting and host defenses in mass mortality of oaks

接种病原菌的橡树幼苗在接种部位附近电导率明显降低，而远端电导率变化不明显。接种苗和离体苗在向远端供水时，枯萎病的发育都被延缓，这表明局部水分堵塞是枯萎的机制。接种真菌后，枯萎前期蒸腾作用下降。未观察到木材变色/真菌的轴向传播与枯萎病发生之间的关系。虽然接种部位附近的水分含量有所下降，但无导水区距离干燥区较远，表明该病没有发生明显的空化现象。在通过无水传导区域的血管中观察到泰洛氏杆菌作为汁液上升阻塞的因素。防御反应尽管提取物的抗真菌活性在…中没有增加较多的反应区屏障、沉积衬里或遮挡木质部成分的现象显著。木质素类化合物和果胶分别是纤维区、小导管和管胞区域的主要成分。还观察到了酚类、对苯二酚和脂类。接种后3d，木质部纤维闭塞，1周后形成空间连续屏障。2周后，类固醇损失、胞化和酚类物质积累显著增加。反应区势垒处木质素含量增加。木质素含量增加的主要原因是凝聚木质素，可能来源于富含愈创木酰基的木质素。感病和抗病树种的反应特征为研究壳斗科树种间防御反应的差异。只有锯缘栎苗和皱叶栎苗枯萎。敏感度的差异与木材变色的切向传播一致，但与轴向传播无关。较少

Mechanisms of wiltingWater conductivity was conspicuously reduced near the inoculation site of oak seedlings inoculated with the pathogenic fungus Raffaelea quercivora, while the conductivity did not change in the distal part. Wilt development was delayed in both inoculated seedlings and excised seedlings when water was supplied to the distal part, suggesting local water blockage as the wilt mechanism. Transpiration decreased in the early stage of wilting after the fungal inoculation. No relationship was observed between axial spread of wood discoloration / fungi and wilt development. Although water content decreased in very adjacent area to the inoculation site, the area without water conduction extended further from dry zone, suggesting that no marked cavitation occur in this disease. Tyloses were observed in vessels which passed through the area without water conduction as the factor of sap ascent blockage.Defense responsesAlthough antifungal activity of extracts did not increase in … More reaction zone barrier, deposits lining or occluding xylem elements were remarkable. Lignin-like compound and pectin were major constituents in fiber region and in small vessel and tracheid region, respectively. Phenols, quinones and lipids were also observed. Fiber occlusion in the xylem was observed 3 days after the inoculation, and spatially continuous barrier was formed after one week. Tyloses, suberization and phenols accumulation became remarkable after 2 weeks. Lignin content increased at the reaction zone barrier. Most of increased lignin was attributed to condensed lignin, probably originated from guaiacyl-rich lignin.Characteristics in the responses of susceptible and resistant treesTo investigate the differences in defense responses among Fagaceae species, seedlings of several species were inoculated with R.quercivora. Only Quercus serrata and Q.crispula seedlings wilted. Differences in susceptibility coincided with tangential spread of wood discoloration, but not with the axial spread. Less