In this article we will discuss about the modes of reproduction in pyronema which belongs to class ascomycetes.
The vegetative body of the fungus is a mycelium which is made up of superficially growing, very sparsely branched hyphae. The hyphal cells are rather short and multinucleate.
Pyronema reproduces both asexually and sexually.
During asexual reproduction some of the hyphae from the vegetative body stand erect and cut off chains of conidia from their tips. Each conidium is capable of giving rise to a new mycelium on germination.
Pyronema is a homothallic fungus with well-developed sex organs. Though the vegetative hyphae are rarely branched, some of them which bear the sex organs, become forked at one or more points. From these forkings lateral branches develop in upward directions forming tufts.
These hyphae then branch repeatedly in a dichotomous fashion, and the ultimate cells of each pair become converted into an antheridium or an ascogonium. The antheridium is clavate in form and is borne upon one or two stalk cells. The stalk cells are uninucleate, while the antheridium is multinucleate. In the female branch, similarly, the balloon-shaped swollen, multinucleate ascogonium is borne on one or two stalk cells.
From the distal end of the unicellular ascogonium a curved, tubular unicellular but multinucleate structure, the trichogyne, is produced. As the sex organs mature, the nuclei in both the antheridium as well as the ascogonium enlarge in size; those in the trichogyne, however, remain minute and do not increase in size, and finally disintegrate.
The trichogyne comes in contact with the antheridium and dissolution of walls at the point of union, takes place. Meanwhile, the nuclei of the trichogyne are degenerated, and the antheridial nuclei with some amount of cytoplasm migrate into the trichogyne. Now the common wall in between the trichogyne and the ascogonium also undergoes disorganization, and the ascogonial nuclei move towards the centre of the ascogonium.
From the trichogyne the antheridial nuclei with the cytoplasm then migrate into the ascogonium and lie in close association with the ascogonial nuclei. Though plasmogamy takes place immediately, the actual fusion of the male and female nuclei in pairs remains a very much debatable point.
Some workers consider that karyogamy occurs within the ascogonium, and as a result the nuclei become diploid, while others are of opinion that the male and female nuclei simply lie in pairs or in small groups in very close proximity but do not fuse. The present-day wokers favour the latter view.
Within a few hours of the aforesaid process the ascogonium becomes invested by peridium, which an envelope is formed by the vegetative hyphae originating form the lower cells of the tuft. Simultaneously, a large number of which develops into an ascogenous hyphae.
From the ascogenous hypha the ascus is developed by the usual crozier formation. Lying intermingled with the asci there are unicellular filamentous paraphyses. Each ascus contains eight haploid ascospores. Each ascospore, on being forcibly liberated from the ascus, forms a new mycelium on germination.
It is to be noted, however, that in P. confluens the mature apothecium is in reality a compound apothecium. This is due to the fact that in this species a large number of sex organs are produced very close to one another, and consequently some of the developing fruit bodies fuse among themselves. The apothecium is of the hemiangiocarpic type.
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