Reproduction in Ascobolus | Ascomycetes | Fungi | Botany

In this article we will discuss about the modes of reproduction in ascobolus which belongs to class ascomycetes.

The mycelium of the fungus consists of much-branched, septate, hyphal cells with protoplasm, and a considerable amount of oil drops as reserve foods.

A. magnificus reproduces both sexually and asexually.

Though the fungus is morphologically homothallic and bears both types of sex organs, antheridia and ascogonia, yet it is self-sterile, because union does not take place between the sex organs of the same mycelium; only the sex organs of two complementary mycelia unite with each other.

In this sense, the fungus is phy­siologically heterothallic and cross-fertile. As a result of this union, the fruit body, the apothecium, is formed. The male sex organs, the antheridia, and the female sex organs, the ascogonia, may develop from the hyphae of both the complementary strains. The antheridium is multinucleate, and more or less clavate or cylin­drical in form.

The ascogonium, on the other hand, is also multi­nucleate, and a globose structure with a terminal septate portion, the trichogyne. When the antheridium and the ascogonium of the complementary strains meet, the trichogyne first twists round the antheridium, and a passage is established in between the antheri­dium and the terminal cell of the trichogyne. The male nuclei then travel through the trichogyne, and fuse in pairs with the female nuclei in the ascogonium.

After fertilization, numerous ascogenous hyphae begin to develop from the ascogonium, and a number of paired nuclei enter into them. As the ascogenous hyphae elongate, they undergo septation. The ascus develops from the binucleate penultimate cell of each ascogenous hypha by the usual crozier formation method.

The eight as­cospores of each ascus are ultimately dis­charged, and they ger­minate under favour­able conditions to form new mycelia. During the sexual union, seve­ral vegetative hyphae grow up surrounding the sex organs, unite, and there finally arises a fleshy, cup- or saucer-shaped fruit body, known as the apothe­cium. Common genera are Helvella, Morchella, etc.

A vertical section through an apothecium shows that the concave surface of the cup is lined by hymenium and the basal portion is composed of a mass of sterile hyphal tissue (Fig.180). The hymenium consists of cylindrical asci interming­led with septate hyphae, the paraphyses.

Each ascus contains 8 brown, ellipsoidal and hyaline ascospores, arranged uniseriately. The mature asci, before spore-discharge, stand well above the level of the hymenium (Fig. 180). When the spores attain maturity, the apices of asci usually open by lids, through which the ascospores are liberated. Each ascospore falling on a suitable substratum germinates and gives rise to a new mycelium.