plant surface microbiology.pdf

15 Interaction of Piriformospora indica with Diverse Microorganisms and Plants 259
From 10 days after inoculation on, some hyphae formed irregular, globular
swellings, which were called coralloid hyphae (Fig. 16). These hyphae preceded
the production of chlamydospores, which were produced terminally.
Mature spores could be found from 17 days after inoculation on. On the surface
of rhizodermal cells occasionally slightly swollen hyphal tips could be
observed. In some cases an imprint in the host cell wall was visible, probably
caused by mechanical pressure in combination with enzymes, indicating an
appressorial function of these hyphal tips (Fig. 16). In some host cells intracellular
hyphae could be found and at the penetration point, the hyphae had
generally reduced their diameter. Host cell wall thickenings as an answer to
the penetration could never be observed. Like hyphae of the external
mycelium, intracellular hyphae formed coralloid swellings and sometimes
also produced chlamydospores. A necrotrophic potential of P. indica could be
demonstrated by vitality tests. Control roots and regions, which were free
from mycelium were always stained bright green, which indicated the vitality
of the corresponding cells. Root areas that were covered with hyphae often
showed weaker or no fluorescence (Fig. 16). This indicates that the fungus is
able to cause local damage to the root cortex of this host.
4.10 Root Organ Culture
Root organ culture of Daucus carota L. (carrot) was prepared as described by
Bécard and Piche (1992). P. indica interacted with the root organ culture of
carrot in the same way as was found in other plants tested. The infection rate,
as a portion of infected root length, has been calculated to be 17 % 9 weeks
after inoculation, 50 % in the most successful culture and 40 % after pro-
Fig. 17a–c. Interaction with transformed Daucus carota (Queen Anne’s-lace) root. Root
organ cultures were inoculated with P. indica and grown for 20 days. a Dark circles represent
the place for inocula; b hyphae and chlamydospores on the surface of the roots; c
intracellular sporulation as seen with the LM