Life cycle of phytopthora

1. Life Cycle of
Phytophthora
BY
JAVED AHMAD
Department of Biotechnology, JMI

2. Mycelium of Phytophthora:
 It is profusely branched and consists of
aseptate, hyaline, profusely branched,
coenocytic
 Moderately thick hyphae about 4-8µ in
diameter.
 Glucans is the predominant material in the
hyphal wall. Cellulose is a minority
component or even lacking altogether.
 The plasma membrane is distinct and is seen
as a dark line at the periphery of the hyphal
protoplasm.

3. The cytoplasm contains scattered
nuclei, dictyosomes, lomasomes,
mitochondria, endoplasmic
reticulum, ribosomes and many large
vacuoles with lipid inclusions.
The fungal hyphae ramify in the
intercellular spaces between the cells
of the host tissue. These are called
the intercellular hyphae.

5. Haustoria of Phytophthora:
The haustoria are variously shaped
intracellular feeding structures. In P. infestans
they are small globes, occasionally short,
straight or curved pegs. There may be one or
more haustoria in each host cell. The
intracellular haustorium relates to the
intercellular hypha by a neck-like constriction
at the penetration site. Thus the long
haustorial stalk or neck usually associated
with this organ is lacking.

6. ASEXSUAL REPRODUCTION
Because P. infestans is a host-specific parasite, it needs plant
tissue to grow in.
Usually, as was the case in Ireland, P. infestans reproduces
asexually.
Its life cycle usually begins as the sporangia are carried by
the wind, land on plant tissue, and release their zoospores.
 This will happen when the conditions are wet and cool and
is called indirect germination.
These spores are biflagellated—having both a tinsel and
whiplash flagellum which is characteristic of oomycota and
will swim until they encyst in the host.
When conditions are warmer, P. infestans will infect the
plant by direct germination—that is a germ tube will form
from the sporangium and will penetrate the host tissue
allowing it to gain nutrients from its host.

7. Sexual reproduction, can and does
occur when both mating types are
present. The antheridium and oogonium
(the only haploid parts in the life cycle of P.
infestans) nuclei will fuse together
(karyogamy) when the antheridium enters
the oogonium. They will form a diploid
oospore, which will develop into a
sporangium and the cycle will continue as is
would asexually.