Histopathological studies of sclerotia of phytopathogenic fungi parasitized by a GFP transformed Trichoderma virens antagonistic strain

The gfp gene from the jellyfish Aequorea victoria coding for the Green Fluorescent Protein (GFP) was used as a reporter gene to transform a Trichoderma virens strain, I10, characterized by having a promising biocontrol activity against a large number of phytopathogenic fungi. On the basis of molecular and biological results, a stable GFP transformant was selected for further experiments. In order to evaluate the effects of GFP transformation on mycoparasitic ability of T. virens I10, sclerotia of Sclerotium rolfsii, Sclerotinia sclerotiorum and S. minor were inoculated with the I10 3.4.10 GFP transformant or the wild type strain. Statistical analysis of percentages of sclerotia decayed showed that transformation of the antagonistic isolate with the GFP reporter gene did not modify mycoparasitic activity against sclerotia. Sclerotium colonization was followed by fluorescent microscopy revealing intra-cellular growth of the antagonist in the cortex (S. rolfsii) and the inter-cellular growth in the medulla (S. rolfsii, S. sclerotiorum). The uniformly distributed mycelium of T. virens just beneath the rind of sclerotia of both S. rolfsii and S. sclerotiorum suggests the sclerotia became infected at numerous randomly distributed locations without any preferential point of entry.