Elucidation of the Biological Function and Early-Infection Cell Cycle Regulatory Mechanism of Avocado-Infecting...

Persea americana (avocado) is a fruit rich in nutrients; however, its industry is facing major threats from pathogen infection. Here, we clearly identified Colletotrichum fructicola as the pathogen causing avocado diseases in Pu'er City, Yunnan Province. However, the biological characteristics, genetic transformation system, and early cell cycle regulation of this pathogen remained unclear. In this study, C. fructicola exhibited a maximum growth rate on complete medium (CM), with the conidial yield reaching 2 × 10⁵ conidia/mL after 24 h in liquid CM. Conidia of C. fructicola had nearly fully germinated at 4 h post-inoculation (hpi), with the appressorium formation rate exceeding 95% at 12 hpi. We also established a PEG-CaCl₂-mediated genetic transformation system. The GFP-tagged transformants showed no significant differences in core biological function from the wild type. Using eGFP labeling, we visually elucidated the early cell cycle regulation of C. fructicola. Furthermore, cell cycle inhibitor assays demonstrated that C. fructicola conidial germination is independent of nuclear division and relies on cytoskeletal modulation, whereas appressorium formation and mycelial expansion require functional cell cycle regulation. This is probably the first study to systematically elucidate the cell cycle regulatory characteristics of C. fructicola isolated from avocado, and to successfully develop its genetic transformation system. These results provide important theoretical and technical support for the formulation of integrated control strategies against C. fructicola, as well as facilitating the sustainable development of the avocado industry.