DMSO is used for dilution purpose, so you can use DMSO without any dilution and prepare 10-100 mg/ml concentration of your plant extract for application.
Which method you are using for your experiment? In my opinion for disc diffusion or well diffusion method you can use 100 micro liter of 10-100 mg/ml plant extract (prepared in DMSO). that will be easy sophisticated.
And if your plant extract (2 gm /100 ml DMSO) are responsible for fungus growth inhibition then try less than concentration you applied.
Hope so this information can helpful for your research.