1 research outputs found
Light and electron microscope studies of host-parasite relations in a mycoparasite
Light microscope studies of the mycoparasite Piptocephalis
virginiana revealed that the cylindrical spores of the
parasite became spherical upon germination and produced 1-4
germ tubes. Generally t"l.vO germ tubes were produced by each
spore. When this parasite was inoculated on its potential
hosts, Choanephora cucurbitarum and Phascolomyces articulosus,
the germ tube nearest to the host hypha continued to grow and
made contact with the host hypha. The tip of the parasite's
germ tube became swollen to form a distinct appressorium. Up
to this stage the behavior of the parasite was similar regardless
of the nature of the host. In the compatible host-parasite
combination, the parasite penetrated the host, established a
nutritional relationship and continued to grow to cover the
host completely with its buff colored spores in 3-4 days. In
the incompatible host-parasite combination, the parasite
penetrated the host but its further advance was arrested. As
a result of failure to establish a nutritional relationship with
the resistant host, the parasite made further attempts to
penetrate the host at different sites producing multiple
infections. In the absence of nutrition the parasite weakened
and the host outgrew the parasite completely. In the presence
of a non-host species, Linderina pennispora the parasite
continued to grow across the non-host 1).yp_hae vlithout establishing
an initial contact. Germination studies showed that the
parasite germinated equally well in the presence of host and
non-host species.
Further electron microscope studies revealed that the
host-parasite interaction between P. virginiana and its host,
C. cucurbi tarum, was compatible when the host hyphae were young
slender, with a thin cell wall of one layer. The parasite
appeared to penetrate mechanically by pushing the host-cell wall
inward. The host plasma membrane invaginated along the involuted
cell wall. The older hyphae of C. cucurbitarum possessed two
distinct layers of cell wall and-showed an incompatible interaction
when challenged vlith the parasite. At the point of
contact, the outer layer of the host-cell wall dissolved,
probably by enzymatic digestion, and the inner layer became
thickened and developed a papilla as a result of its response to
the parasite. The haustoria of the parasite in the old hyphae
were always surrounded by a thick, well developed sheath, whereas
the haustoria of the same age in the young host mycelium
were devoid of a sheath during early stages of infection.
Instead, they were in direct contact with the host protoplast.
The incompatible interaction between a resistant host, P.
articulosus and the parasite showed similar results as with the
old hyphae of C. cucurbitarum. The cell wall of P. articulosus
appeared thick-with two or more layers even in the 18-22 h-old
hyphae. No contact or interaction was established between the
parasite and the non-host L. pennispora. The role of cell
wall in the resistance mechanism is discussed