Abstract: This study investigated the colonization capacity of Beauveria bassiana in peanut plants using green fluorescent protein labeling. The plasmid pCAMB-gfp carrying the gfp gene was introduced into B. bassiana strain B16-5-1 via Agrobacterium-mediated genetic transformation. The transformed fungus exhibited bright green fluorescence under an excitation wavelength of 488 nm, and the gfp gene was stably integrated into B16-5-1, resulting in the construction of the B16-5-1-gfp strain. A pot experiment with root irrigation inoculation was conducted to determine the colonization of B16-5-1-gfp in peanut plants, which was confirmed by nested PCR showing colonization persisting for up to 35 days. Furthermore, laser scanning confocal microscopy observations at 4 hours post-inoculation detected distinct fluorescence in the roots, stems, and leaves, indicating rapid upward translocation of the fungus from the roots to the leaves via the vascular system. Significant spatial and temporal variation in colonization density in different tissues was detected through fluorescence intensity quantification using ImageJ software. . Fluorescence intensity was significantly higher in the roots than in other tissues, peaking at 1988.13 on day 7. Fluorescence in the leaves peaked later, reaching 742.47 on day 21, while intensity in the stems was lower, with a maximum of 305.95 on day 7. By establishing a B. bassiana-peanut symbiont system, the plant growth-promoting effects of the marked strain B16-5-1-gfp were evaluated through measuring above-ground (fresh weight, dry weight, plant height) and below-ground (fresh weight, dry weight, root length) parameters. All inoculation treatments promoted peanut growth, but the effects varied depending on the application timing and method. At the sowing stage, Seed Dressing exhibited the most significant growth-promoting effect on both aboveand below-ground parts. Broadcast Application was the second most effective, significantly increasing plant height and above-/below-ground dry weight compared to the control. The overall efficacy at the sowing stage ranked as: seed dressing>broadcast application. At the seedling stage, Foliar Spraying showed the most pronounced growth promotion. Root drenching was the second most effective, significantly enhancing above-ground metrics compared to the control, with a positive trend also observed below-ground. Broadcast application had a relatively weaker effect; it significantly increased seedling height and above-ground fresh weight but not dry weight compared to the control, and no significant differences were found in below-ground parameters. The overall efficacy at the seedling stage ranked as: foliar spraying>root drenching>broadcast application. This study demonstrates that B. bassiana B16-5-1 can colonize and systemically translocate within peanut plants, indicating strong endophytic potential. Furthermore, different inoculation methods applied at varying growth stages differentially influence plant growth, with seed dressing at sowing and foliar spraying at the seedling stage proving to be the most effective strategies for promoting peanut growth.

Key words: peanut, Beauveria bassiana, green fluorescent protein, colonization, growth promotion