In this article we will discuss about the modes of reproduction in albugo candida which belongs to class phycomycetes.
It is a much-branched, intercellular, coenocytic mycelium with rather coarse hyphae, which bear numerous small, rounded, intercellular haustoria within the neighboring cells.
Albugo reproduces both asexually and sexually. During asexual reproduction, hyphae collect beneath the epidermis and form closely-packed groups of simple or branched, club-shaped structures (conidiophores or sporangiophores) forming a palisade-like layer, which pushes the epidermis outwards to form whitish blister-like areas, called sori.
Each club-shaped structure cuts off successively from its apex, a chain of globular bodies (conidia or sporangia), each with five to six nuclei. They are separated from one another by short neck-like projections of some gelatinous material. As the chains elongate, they press the epidermis above and ultimately it becomes ruptured. The globular structures successively break off and are easily disseminated by the wind.
Each globular body, under favourable conditions, germinates directly by the production of germ tubes and behaves as a conidium or indirectly by the production of zoospores and functions as a sporangium. In presence of water and a low temperature, the zoospores are produced, but in a relatively dry condition the germ tubes are formed. In the latter case, the germ tube may enter into various parts of plants and bring about infections.
When germination takes place indirectly, the contents of a sporangium, by the process of cleavage, form 4-8 zoospores, which either escape, one by one, through a pore formed on the wall of the sporangium, or an adherent mass of zoospores is discharged into a vesicle formed by the sporangium itself. The vesicle eventually disappears and the zoospores are set free. The zoospores are ovate to slightly kidney-shaped in form and each bears two unequal flagella.
After a period of swimming, a zoospore comes to rest, its flagella disappear and a wall is secreted around the protoplast. It then germinates directly by forming a germ tube, which usually enters through a stoma and brings about infection.
Sexual reproduction takes place by oogamy. Both antheridia and oogonia develop within the host tissues, particularly in those of the flowers and axes of the inflorescences. The sexual process is essentially similar to that of Pythium de Baryanum but differing in detail. In this case, more periplasm is formed and the female nucleus lies in a deeply-stainable mass of cytoplasm at the centre of the ooplasm.
After fertilization when the zygote is formed, zygote nucleus divides, soon after its formation, into about 32 nuclei so that the resting oospore is multinucleate. There is evidence that the reduction division takes place during the division of the zygote nucleus.
Under favourable conditions when the oospore germinates, its outer wall ruptures partly exposing an internal transparent sac-like structure containing zoospores. This sac finally ruptures and biflagellate zoospores are set free, which may eventually bring about infection.
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