Abstract:

Objective: In this study, we investigated the influence of different host tree species on the types of symbiotic fungi of Sirex nitobei, and the antagonistic effect of dominant fungi on the body surface of the dead S. nitobei larvae in the host Pinus sylvestris var. mongolica on symbiotic fungi of S. nitobei, in order to explore the causes of death of S. nitobei larvae in the host tree from a microscopic perspective, so as to offer new ideas and basis for biocontrol of S. nitobei. Method: According to morphological characteristics and ITS sequences, the species of symbiotic fungi in different host tree species were identified, and the antagonistic ability of dominant endophytic fungi of Phlebiopsis gigantea and Trichoderma viride against symbiotic fungi (Amylostereum chailletii and A. areolatum) of S. nitobei was determined by plate confrontation, fermentation broth test and microscopic observation. Result: The symbiotic fungi of A. chailletii and A. areolatum were isolated from different host tree species, but the detection rates of two symbiotic fungi of S. nitobei were significantly different. The wasps in P. sylvestris var. mongolica were more likely to carry A. chailletii, while the wasps in P. tabulaeformis were easier to carry A. areolatum. The growth rate of the two endophytic fungi was faster than that of symbiotic fungi, of which Trichoderma viride had the fastest growth rate and symbiotic fungus of A. areolatum had the slowest growth rate. Both Trichoderma viride and Phlebiopsis gigantea were able to inhibit the growth of symbiotic fungal hyphae, and they wrapped, parasitized or interspersed on the symbiotic fungal hyphae, resulting in the distortion, deformation and abnormal expansion of symbiotic fungal hyphae. Eventually, the two endophytic fungi completely covered the colonies of symbiotic fungi, which caused the symbiotic fungi to be unable to grow and die. The fermentation broth of two endophytic fungi inhibited the conidial germination of symbiotic fungi of A. chailletii and A. areolatum. The inhibitiory effect of Trichoderma viride fermentation broth was higher than that of Phlebiopsis gigantea fermentation broth, furthermore, the higher the dilution ratio of fermentation broth, the worse the inhibitory effect. Conclusion: The two endophytic fungal species have strong antagonistic effects on the symbiotic fungi of S. nitobei, and these endophytic fungal hyphae can completely inhibit and kill the symbiotic fungal hyphae. The research results would provide available fungal strains for the biological control of S. nitobei.

Key words: Sirex nitobei, symbiotic fungi, endophytic fungi, inhibitory effect