Fig tree populations have been in steady decline throughout many countries. Among the many potential causes, fig-wilting disease stands out as a major issue. As previously mentioned, the ambrosia beetle Euwallacea interjectus is responsible for spreading the fungus Ceratocystis ficicola that is responsible for causing the sickness.
Now, researchers from central Japan’s Nagoya University have discovered a second fungus, Fusarium kuroshium, that is harmless on its own but devastating to fig trees when detected in the presence of C. ficicola.
Multiple additional fungi have been hypothesized to have a role in fig-wilting disease alongside recognized pathogens like C. ficicola. Among them is Fusarium kuroshio, often known as F. kuroshio, an infectious agent of fig and avocado plants. Fungi have long been suspected of spreading illness because they are commonly seen on the heads of wild and bred E. interjectus adult females, where they can be stored in a specialized organ.
Dr. Zi-Ru Jiang and Associate Professor Hisashi Kajimura from Nagoya University’s Graduate School of Bioagricultural Sciences collaborated with the Hiroshima Prefectural Institute of Technology, Kobe University, and the Forestry and Forest Products Research Institute to inoculate fig saplings with various combinations of fungi collected from E. interjectus to determine whether or not the fungi are related to the damage of the fig trees.
For comparison, they used Neocosmospora metavorans, a fungus that can live on a variety of plants (including avocado and Robusta coffee). Among the saplings, some received only one of the three fungus, while another group received both F. kuroshium and C. ficicola.
Saplings infected with C. ficicola perished, as predicted, but those infected with either N. metavorans or F. kuroshium alone did not, indicating that these two fungi are not hazardous to fig trees. In contrast, the saplings in the combination group withered less than two weeks after infection and had a greater area of dead wood. The drooping of the saplings appears to have been facilitated by a symbiotic relationship between F. kuroshium and C. ficicola.
The research results were published in Microorganisms.
In the event of widespread beetle infestations and lowered resistance in host trees, fig-wilting disease symptoms may develop as a result of the ambrosia beetle and its fungus. This suggests that research into the interactions between C. ficicola and its symbionts might help inform the design of more effective methods for preventing and controlling illness according to the researchers.
Synergistic effects are caused by their presence with companion fungus, and they have a greater damaging effect on fig trees than the companion fungi alone, according to this study, suggesting that symbiotic fungi do not harm fig trees on their own. This finding opens up new opportunities for intervention and yields useful insights for enhancing pest management strategies in the future.
Sources:
Zi-Ru Jiang et al. (2022). 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, Microorganisms. DOI: 10.3390/microorganisms10101912
