Rice blast is caused by the Ascomycete fungus, Magnaporthe
grisea Barr (anamorph Pyricularia grisea Sacc., synonym P.
oryzae Cav.). Pyriform macroconidia, ca. 20 ´ 10 mm, (Figure
1) are produced on conidiophores which protrude from
lesions on plants. These germinate and develop an appressorium
(Figure 2) at the tip of the germ tube, which attaches to
the surface of plant tissues; an infection-peg from the
appresorium penetrates into plant tissues. The wall of conidiophores
and appressorium are pigmented by melanin.