Toxin Accumulation of Three Leymus mollis-associated Endophytic Fusarium Isolates and Their Effects on Growth and Salt Tolerance of Liquidambar styraciflua Seedlings

Objective To evaluate the potential use of endophytes from extreme conditions as novel probiotics in improving salt tolerance of tree seedlings.

Method The effects of three endophytic Fusarium isolates, recovering from the halophytic Leymus mollis, on the growth and salt tolerance of Liquidambar styraciflua seedlings were investigated. The three isolates were identified through morphological description and molecular phylogeny. In vitro toxin production of the endophytic Fusarium isolates were analyzed. The co-culturing system was used to investigate the binary interactions between gnotobiotic seedlings and Fusarium isolates under normal and saline conditions. Tissue staining method was applied to examine the fungal infection structures formed in roots.

Result Two Fusarium isolates were identified to F. culmorum (Class2-1B) and F. pseudograminearum (Class2-1C), and the other one (Class2-3) was not currently identified to the species level. In comparison to two pathogenic Fusarium species, the Class2-1B and Class2-1C only produced very low level of several toxins, while the Class2-3 produced a large amount of enniatine. Both Class2-1B and Class2-1C exhibited an extensive colonization pattern in roots, but the hyphae of the Class2-3 seldom entered the inner root tissues and just distributed around the root surface. Inoculation experiment confirmed that the biomass, seedling height, root length and number of leaves in plants treated with either Class2-1B or Class2-1C were higher than the control group, although not all differences reached the significant level. In contrast, the plant growth was obvious inhibited in the presence of the Class2-3. Under salinity stress, it appeared that most seedlings inoculated with either the Class2-1B or Class2-1C were more salt tolerant, particularly for the Class2-1B treatment, than the control and mixed inoculation groups as evidence by the salt injury index. However, the chlorophyll contents in all treatments did not differ significantly.

Conclusion The degree of endophytic Fusarium-mediated plant growth and salt tolerance mainly depends on different Fusarium species. The result of the study, at least in part, demonstrates that the positive or negative effect of endophytic Fusarium on plants might be related to the type and content of the toxins they produced.