Abstract
Ragweed (Ambrosia artemisiifolia L.), an invasive species, is well-known for its rapid growth, strong reproductive potential, and high stress tolerance. The evolutionary distinctiveness and strong ecological adaptability of Ambrosia have enabled the endophytic fungi that coevolved with it to become valuable microbial resources. In this study, one of the endophytic fungi isolated from ragweed was named strain V3. Strain V3 was identified as Chaetomium sp. (Ascomycota) based on morphological characteristics and molecular analyses. The strain V3 promotes tomato growth by significantly increasing plant height, root length, the number of lateral roots, and chlorophyll content, effectively enhancing photosynthesis and consequently improving fruit yield. Meanwhile, compared to the control, tomato fruits inoculated with strain V3 exhibited significantly higher levels of vitamin C (VC) and lycopene, indicating a notable enhancement in fruit quality. Additionally, strain V3 is capable of producing phytohormones, including indole-3-acetic acid (IAA), gibberellin (GA(3)), and zeatin, and of regulating the expression of tomato auxin response factor (ARF) genes. This study demonstrates that strain V3 has the potential to promote tomato plant growth.