In this article we will discuss about Sexual life cycle phytophthora infestans life cycle of phytophthora with the help of suitable diagrams. The hyphal wall is approximately 0. It is electron transparent except for a thin, electron dense outer surface. Glucans is the predominant material in the hyphal wall.
Cellulose is a minority component or even lacking altogether. Hunsley and Burnett reported that in Sexual life cycle phytophthora infestans hyphal wall of P. The plasma membrane is distinct and is seen as a dark line at the periphery of the hyphal protoplasm. It is undulating and frequently forms lomasomes.
It is appressed to the inner surface of the hyphal wall. The cytoplasm contains scattered nuclei, dictyosomes, lomasomes, mitochondria, endoplasmic reticulum, ribosomes and many large vacuoles with lipid inclusions. Scattered throughout the cytoplasm are the lipid bodies more numerous in the old hyphae. Septa remain suppressed in the vigorously growing hyphae. They, however, appear here and there in the old hyphae or in connection with the formation of reproductive organs.
The fungus spreads through tissues of leaves, stems and tubers. The fungal hyphae ramify in the intercellular spaces Sexual life cycle phytophthora infestans the cells of the host tissue. These are called the intercellular hyphae. In addition there are hyphae that penetrate, traverse and eventually leave the cell. These are called the intracellular or transcellular hyphae. The transcellular hyphae emerge from the host cell into an intercellular space directly into a Sexual life cycle phytophthora infestans host cell.
The intercellular and transcellular hyphae have similar ultrastructure. Haustoria develop on the intercellular hyphae when the latter come in intimate contact
Sexual life cycle phytophthora infestans primary walls of the host mesophyll cells. The hyphal wall is tightly pressed against host cell wall in this region which is called the penetration site.
Coffey and Wilson found prior to haustorial development lobed hemispherical deposit of moderately electron-dense amorphous material termed the penetration matrix is laid in this region of incipient penetration.
The bulging hyphal wall is intact in this region. The fibrillar network of the host wall, however, is no longer seen. It is replaced by the penetration matrix which is bounded by the host plasma membrane next to which is a thin band of host cytoplasm. An infection peg arises from the hyphal bulge. It makes its way into the host cell pushing in front the host cell plasma membrane and the host cytoplasm.
Within the host cell the infection peg expands at its tip to form the haustorium. The haustoria are variously shaped intracellular feeding structures. There may be one
Sexual life cycle phytophthora infestans more haustoria in each host cell.
The intracellular haustorium is connected with 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. The electron-transparent haustorial wall is continuous with that of the Sexual life cycle phytophthora infestans hypha and so is the haustorial plasma membrane which encloses the anucleate haustorial cytoplasm containing a few mitochondria, lipid bodies and sparse endoplasmic reticulum.
Surrounding the Sexual life cycle phytophthora infestans, in close association with the haustorial wall, is a sheath of electro-dense amorphous material. It separates the haustorial wall from the host cytoplasm and thus forms the pathogen host interface between the fungal parasite and the host plant. The nature, origin and function of sheath matrix is still uncertain. extra haustorial sheath is delimited from the host cytoplasm by a tightly pressed unit membrane termed the extra haustorial membrane.
The latter is considered the invaginated host
Sexual life cycle phytophthora infestans membrane. Hohl and Stosselhowever, found some haustoria covered by an additional layer of electron-transparent wall material between the extra-haustorial matrix and the extra-haustorial membrane. It is termed the wall apposition A. The wall apposition is continuous with the host cell wall at its base.
It may partially or completely surround the haustorium. Hohl and Sutter supporting Hohl and Stossel observed that wall apposition may or may not be formed. Coffey and Wilson reported that at an early stage the haustoria do not possess Sexual life cycle phytophthora infestans or encasements.
The haustoria are more commonly found in the tubers. In severe cases of infection the entire plant above the ground is killed. The fungus passes winter in the form of mycelium in infected potato tubers.
With the onset of favourable conditions of warm, damp weather in spring a tuft of slender, branching hyphae arise from the internal mycelium. They push their way out either through a stoma A or by piercing through the epidermal cell on the lower surface of Sexual life cycle phytophthora infestans leaf.
In the case of the tubers they push their way through the lenticels or injured portions of the skin. These aerial hyphae are hyaline, and sympodially branched and are of indeterminate growth.
These special branched aerial hyphae are called sporangiophores conidiophores. Phytophythom, Sexual life cycle phytophthora infestans, differs from other members of the family in having sporangiophores distinct from the somatic hyphae.
The sporangium is formed by the inflation of Sexual life cycle phytophthora infestans tip of the side branch of the sporangiophore B 1. The multinucleate inflation is then off by a transverse septum basal plug as a sporangium. The hyphal branch bearing the young terminal sporangium continues to grow B As the sporangium reaches maturity, the branch tip swells slightly just below the sporangium and proliferates pushing the sporangium to the side as the elongation proceeds B4.
The process may be repeated. The sporangia are, thus, borne terminally but are subsequently Sexual life cycle phytophthora infestans to a lateral position. The mature sporangia are lightly attached, the sporangiophore of Phytophthora is, therefore, sympodially branched. It bears nodular swellings B5 Sexual life cycle phytophthora infestans denote the points of detachment of sporangia. These swellings give the branched sporangiophore a jointed appearance characteristic of the genus.
According to Crosier temperature and humidity govern sporangial production. Under continuous light conditions no sporangia are produced
Sexual life cycle phytophthora infestans the fungus. He found that the inhibiting effect of light was temperature dependent.
High temperature increased it. The mature sporangium is a hyaline, oval to elliptical, thin-walled spore sac with a basal plug. It has a small stalk and an apical papilla.
The sporangial wall is nearly 0. Within the wall is the plasma membrane. It is closely appressed to the sporangial well and encloses the multinucleate cytoplasm which contains the usual cell organelles such as mitochondria, dictyosomes, endoplasmic reticulum and ribosomes. In addition the cytoplasm of the mature sporangium contains Paired basal bodies associated with the nuclei membrane bound packets of microtubules and several types of vacuoles.
The chief among these latter are the cleavage and flagellar vacuoles. The former which are considered to originate from the dictyosomes are randomly distributed in Sexual life cycle phytophthora infestans cytoplasm. The flagella containing vacuolese are arranged along the sporangial wall.
The mature lemon-shaped, pappilate sporangium with a basal plug is readily detachable. Wind, rain splashes or contact with other leaves detach and spread or scatter the ripe sporangia on to the leaves of other potato plants. They may also be washed into the soil The sporangia lose their viability if they fail to germinate within a few hours. Landing on the healthy leaf of a host plant, the sporangia germinate. The main factors governing germination are moisture and temperature. The sporangia are adversely affected by Sexual life cycle phytophthora infestans. According to Cochrane, they perish if the relative humidity falls much below per In the presence of moisture provided by rain or dew, the sporaniga of phytophora infestants germinate either indirectly by producing zoospores and thus functioning as zoosporangia or directly by a germ tube and functioning as conidia.
The ability to germinate directly or indirectly is by temperature. The sporangia lose their vitality to germinate indirectly with increasing age. Young sporangia commonly reproduce by zoospores more readily than
Sexual life Sexual life cycle phytophthora infestans phytophthora infestans sporangia.
Wet, cool soil favours indirect germination of sporangia. According to Hohl
Sexual life cycle phytophthora infestans Hama moto the cleavage —cleavage vesicles which are randomly distributed in the cytoplasm become arranged radially equidistant from the neighbouring nuclei approximating the future planes of cytokinesis.
The flagellar vacuoles are arranged along the sporangial wall axially enjoined to the paired basal bodies. At the time of differentiation of zoospores, the margins of flagellar vacuoles fuse with the coalescing cleavage vacuoles.
The membranes of this system eventually fuse with the plasma membrane delimiting the multinucleate sporangial protoplast into uninucleate daughter protoplasts B and freeing the flagella which Lie between the plasma membrane and sporangial wall.
Each subsequently metamorphoses into a biflagellate zoospore which is reniform. Sexual life cycle phytophthora infestans the two flagella one is of whiplash type and the other tinsel. Ferus reported the development of paddle-like structures at their tips. The flagella arise Sexual life cycle phytophthora infestans the depression on the concave side. The zoospores are set free in a group by the bursting of the apical papilla into a vesicle in P.
Indirect germination of sporangium through the intervention of zoospores is an example of the retention of an ancestral character. Phytophthora is a terrestrial fungus.