The Role of Mycangial Fungi Associated with Ambrosia Beetles ( Euwallacea interjectus ) in Fig Wilt Disease: Dual Inoculation of Fusarium kuroshium and Ceratocystis ficicola Can Bring Fig Saplings to Early Symptom Development.

The ambrosia beetle, , is a wood-boring pest and a vector of , a pathogenic fungus causing fig () wilt disease (FWD) in Japan. The ambrosia fungi, and , have been frequently isolated from heads (including mycangia) of wild and reared adult female , respectively. However, the exact mechanisms driving FWD as well as the interactions between and in fig orchard remain unclear. To verify the role of the mycangial fungi in the FWD progression, fig saplings were subjected to inoculation treatments (T1, ; T2, , reference positive control; T3, ; T4, + , realistic on-site combination). T3 and T4 saplings began wilting approximately 12 days after inoculation, leading to eventual death. Median duration from inoculation to death of the T4 saplings was approximately four days significantly faster than that of the T3 saplings. Xylem sap-conduction test indicated that dysfunction and necrosis area were considerably wider in the T4 saplings than in T3 saplings. These results demonstrate that the synergistic action of and contributed to accelerated wilting in the saplings. Based on these discoveries, we proposed a model for system changes in the symbiosis between and its associated fungi in FWD in Japan.