//You can use any type of water-based primer, such as an emulsion paint or an acrylic primer. This base-coat of primer will help give the top coat a truer shade and will prevent it from being affected by the color of the board. The primer also will combat the MDF's tendency to result in a blotchy, uneven finish because of its porous surface.//
Ric ideally use an mdf primer but you can get away with a coat of normal wood undercoat / primer or even emulsion if you sand first - depends on location and what the eventual end useage will be