Infection and colonization of common bean by EGFP transformants of Fusarium oxysporum f. sp. phaseoli

Fusarium wilt caused by the fungus Fusarium oxysporum f. sp. phaseoli (Fop) is one of the most important diseases of common bean and occurs in many regions of the world. However, there is little available information that could elucidate when and where the fungus attacks common bean plants. To study the colonization of common bean by this fungus, we transformed Fop Brazilian race 2 for egfp gene expression and used these fungal transformants to analyze the colonization process in common bean roots and stems. The combined use of driselase and lysing enzyme was sufficient for Fop mycelium protoplastization. The PEG-CaCl₂ transformation protocol allowed us to obtain stable transformed fungi, with colonies expressing the egfp gene. Regarding colonization by Fop transformants, the fungus grew intercellularly on the root hair epidermis at six days post-inoculation (DPI) and on parenchymal cells at 11 DPI on plants of the susceptible line. At 19 DPI, the fungus reached xylem vessels, blocking water and mineral passage in shoots, resulting in wilt and plant death at 25 DPI. Using fluorescence to mark the fungus revealed details of Fop colonization of common bean tissues.