Microscopic observations of strawberry plant colonization by a GFP-labelled strain of Fusarium oxysporum f. sp. fragariae

Fusarium oxysporum f. sp. fragariae, the causal agent of Fusarium wilt in strawberry (Fragaria ananassa Duch.), is a serious threat to commercial production. To understand the interaction between strawberry and Fusarium oxysporum f. sp. fragariae, we transformed the pathogen with a green fluorescent protein as a labelled gene and Hyg as a selectable marker gene using the Agrobacterium tumefaciens-mediated transformation method. The transformants obtained were stable with strong and uniform fluorescence. A green fluorescent protein-tagged strain with similar phenotype and pathogenicity as the wild-type strain was used to study the infection process on strawberry. The observations indicated that the spores attached to the root surface and infected the roots from germ tubes, while the hyphae produced suction cup-like structures from the hyphal tips to infect the strawberry plants. Once inside, hyphal growth was observed mainly in the epidermal and cortical tissues with only a few hyphae detected in the vascular tissues after colonization.