Pyricularia oryzae is the most important fungus causing blast of rice at different growth stages.

You can also use Magnaporthe oryzae, the fungus that causes rice blast disease

Rice sheath blight (Rhizoctonia solani Kuhn) is the most important soil-borne rice fungal disease you can also use this for antifungal activity in your expariment

Rice blast disease caused by Magnaporthe grisea is one of the world wide distributed and damaging fungi. This fungus poses a high rate of genetic variability. You can use this fungus.

Maqsood Ahmed Khaskheli in some region rice sheath blight (Rhizoctonia solani Kuhn) is also a major problem for rice cultivation.

Abu Barkat Md Gulzar you should focus on the most important rice fungus for your country that will bring benefit for rice grower in your locality.

You can also use Fusarium and Pythium which affects rice at seedling stage.