The morphology of infection structure development of Puccinia
recondita f. sp. tritici on and in susceptible and resistant
wheat lines
inoculated with urediospores was examined by SEM. The germ-tube
extends over the leaf surface and elongates perpendicularly to
the long axis of the leaf. When the germ-tube encounters the stomatal
lip, an appressorium forms over the stoma and the pore is
entered by an infection peg produced on the surface of the appressorium
in contact with the host leaf. At 6 h post-inoculation (hpi),
infection pegs develop terminally substomatal vesicles (SSVs) in the
substomatal chambers of all wheat lines. A septum separates
each SSV from its interconnective tube. A primary infection hypha forms
terminally from the elongated SSV either parallel to the
long axis of the stomatal slit or perpendicular to the leaf surface. When
a
primary infection hypha attaches to a host cell, a septum
forms cutting off the tip of the hypha, delimiting a terminal haustorium
mother cell (HMC) by 12 hpi. Secondary infection hyphae
arise from a position proximal to, and in the proximity of, the HMC septum.
Additional HMCs are formed when a secondary hypha
or a tertiary hypha adheres to a plant cell. Infection sites with HMCs
were
observed at 24 hpi and at subsequent sampling stages.
There were no significant differences between the infection processes on
the
three wheat lines examined in this study.