Introduction: Albizia julibrissin Durazz. is a native species of the plain forests of northern Iran. The fungal disease Fusarium wilt, which is common in A. julibrissin Duraz. has caused significant damage to this valuable species. The causative fungus, Fusarium oxysporum Schltdl., enters through root or crown wounds and leads to disease in the tree. The aim of this study is to investigate and compare the control of Fusarium wilt using Trichoderma fungi and the fungicides carbendazim, tebuconazole, and thiophanate-methyl in laboratory conditions.
Materials and Methods:  Sampling was conducted in the forests of Golestan province to isolate the pathogenic fungus. After disinfection, the samples were transferred to a culture medium (PDA) and placed in an incubator with conditions of absolute darkness and a temperature of 25±2 degrees Celsius. After purification, the samples were transferred to a refrigerator at a temperature of 1±4 degrees Celsius and absolute darkness for species identification. The structure of spores, polyphyllides, monophyllides, macroconidia, microconidia, and chlamydospores were examined. The pathogenicity test involved inoculating the fungi with mycelium tablets into the stems of silk tree seedlings. Three identified Trichoderma isolates from the mycological collection of Gorgan University of Agricultural Sciences and Natural Resources (iso2 T. koningii isolates, 6022 T. atroviridae isolates, and 6011 T. virens isolates) were used to study the antagonistic effect on Fusarium. The percentage of inhibition of pathogen mycelial growth, as well as the diameter growth of fungal colonies in treatments and control, were calculated up to 12 days after treatment. Three fungicides, carbendazim, tebuconazole, and thiophanate-methyl, were used in laboratory conditions at concentrations of 1, 10, and 100 (mg/ml) each to investigate the effect of chemical control on inhibiting Fusarium growth. The experiments were conducted in four replications and three levels in a completely randomized design. Data analysis and statistical analysis were performed using SPSS software, with means compared using the least significant difference (LSD) method at the maximum confidence level.
Results: F. oxysporum was identified from infected samples of nightshade trees, and all three Trichoderma species prevented the complete growth of F. oxysporum. The highest inhibition percentage was observed for T. virens and T. atroviridae species, with 68.87% and 68.12%, respectively, while the lowest inhibition rate was for T. koningii species at 66.75%. In chemical control, thiophanate methyl at concentrations of 1 and 10 (mg/ml) resulted in 19% and 60.5% inhibition, respectively, with complete growth inhibition at 100 (mg/ml). Carbendazim at a concentration of 1 (mg/ml) inhibited pathogen growth by 52%, and at concentrations of 10 and 100 (mg/ml), growth was completely stopped. Tebuconazole also completely halted pathogenic mycelium growth at all three concentrations.
Conclusion: Fusarium fungal disease poses a serious threat to valuable nightshade trees in the plain areas of the northern forests of the country. Given the significant damage to these trees, controlling the pathogen and preserving and developing nightshade trees should be a priority. The study demonstrated that the fungicides carbendazim, tebuconazole, and thiophanate-methyl, along with antagonist fungi Trichoderma (T. virens, T. atroviridae, T. koningii) were effective in reducing and completely controlling the growth of the disease-causing fungus in laboratory conditions. The results indicate a significant difference between chemical compounds and biocontrol agents in combating the Fusarium disease-causing fungus.