Lsystem.animate() shows a blank PlantGL window in Python 3

I recently ported my Python2 code involving OpenAlea mtg and lpy libraries into Python3. With Python3, the Lsystem.animate() now can't invoke PlantGL viewer to show the Lpy animation, instead it shows a blank PlantGL canvas. It was working just fine in Python2 though. Any advice on how to resolve this?    
FYI, Lsystem.plot() plot the image just fine in both Python 2 and Python 3 version. 