Did you tray growing with light/dark cycles? We use CM medium and 12h dark/12h light into a 25ºC chamber. Oatmeal agar is algo a good sporulation medium. All the best.

Dear Julio, thanks foy your answer. 

Generally, we leave the plates for 8 days on continuous light at 25ºC , later we stress manually to accelerate the sporulation. The culture medium is agar-oats.

In M. oryzae, asexual development and conidiation is highly controlled by light conditions. May be you should be careful with it. We never have too much problems but we use to work with Guy11 strain. In other strains or natural isolated strains would be hard to get a strong conidiation. http://www.sciencedirect.com/science/article/pii/S1087184506000867 

You can also write to Prof. Ning Zhang at Rutgers Un. She works with Magnaporthe.

Dear Janson, Thnks for your information.