Table 2.

Comparison of Blast Hyphal Types Involved in Biotrophic Invasion of Rice

Biological Features	Primary Hypha	Bulbous IH	Filamentous IH
Growth style	Filamentous	Pseudohyphal and filamentous	Filamentous
Hyphal diameter	3 to 5 μm	>5 μm	3 to 5 μm
Differentiates from	Appressorial penetration peg	Primary hypha or filamentous IH	IH peg that crosses internal walls
Internalizes FM4-64	Yes	No	No
Has membrane cap	Yes	No	Yes
Viability maintained during lesion formation	No	Yes	Yes

Primary hyphae differentiate into bulbous IH as described by Heath et al. (1990). Bulbous IH include the pseudohyphal forms in the first-invaded cell and the enlarged filamentous to pseudohyphal forms in subsequently invaded cells. Filamentous IH are the thin transient hyphae that grow in cells directly after crossing of internal walls.