Ascobolus: Habitat and Reproduction | Ascomycotina

In this article we will discuss about Ascobolus. After reading this article you will learn about: 1. Habit and Habitat of Ascobolus 2. Vegetative Structure of Ascobolus 3. Reproduction.

Contents:

1. Habit and Habitat of Ascobolus
2. Vegetative Structure of Ascobolus
3. Reproduction of Ascobolus

1. Habit and Habitat of Ascobolus:

Ascobolus is represented by 48 species. It is coprophilous fungus growing on dung of herbivorous animals. A furfuraceus grows on old dung of cow while A. carbon Arius grows on old bonfire sites. In India, Ascobolus is represented by 12 species. Some common Indian species are A. magnificus, A. virdis etc.

2. Vegetative Structure of Ascobolus:

Thallus is represented by mycelium. It is well developed, perennial and consists of profusely branched hyphae. Hyphae are septate and the cells are multinucleate. The hyphae ramify within the substratum and form a complex system which helps in the absorption of the food material for the aerial fruiting bodies called apothecia (Fig. 1). The apothecia are yellowish or greenish when young and purplish brown at maturity.

3. Reproduction in Ascobolus:

Ascobolus reproduces by two methods:

(i) Asexual reproduction

(ii) Sexual reproduction.

(i) Asexual Reproduction:

Formation of Chains of oidia or arthrospores has been seen but these are not of frequent occurrence.The oidia can germinate to from a new mycelium (fig.2.). oidia serve both as sexual spore and male cells.

(ii) Sexual Reproduction:

Sexual reproduction is oogamous (fig. 3). The species of Ascobolus may be heterothellic (A. stercovarius A. immersus) or homothallic (A. crenulatus). Male and female sex organs are called antheridia and ascogonia respectively.

Antheridium:

The antheridium on maturity is club shaped and multinucleate. Antheridial branches which bear antheridia are cylindrical and remain erect.

Ascogonium:

The mature ascogonium is globose and multinucleate (100 or more nuclei). It cuts off terminally a long trichogyne which by separations becomes 5-8 celled structure.

Fertilization:

The trichogyne coils around the body of the antheridium and reaches at the anthcridial tip. The walls of contact between two (tip of antheridium and trichogyne) dissolve (plasmogamy) and the male nuclei pass into the apical cell of trichogyne from which they finally reach the ascogonium. The male and female nuclei arrange themselves in pairs towards the periphery of the ascogonium.

Apothecium or Ascocarp or Fruiting Body:

After plasmogamy the ascogenous hyphae are produced from the fertilized ascogonium. The paired nuclei migrate into these hyphae and transverse walls are then laid down dividing them into several cells. The dikaryotic cell at the tip of ascogenous hyphae divides to form four nuclei.

Walls are formed in such a manner that a terminal or ultimate uninucleate hook cell, a bi-nucleate arch cell (penultimate cell) and a uninucleate stalk or anti-penultimate cell is formed (crozier formation). The two nuclei of the penultimate cell fuse and thus young ascus is formed. The diploid nucleus in the young ascus divides by meiosis and then mitosis to form eight haploid nuclei which get organised into ascospores (Fig. 4).

Mature asci are long, calavate with eight ascopores. The ascopores are one-celled, double-walled, ellipsoidal or spherical, purple or dark brown. Some vegetative hyphae grow up among the ascogenous hyphae and give rise to slender paraphysis. Sheath of sterile hyphae surround the asci and paraphysis and ultimately a cup shaped yellow structure develops. It is called apothecium.

In Ascobolus the development of apothecium is of two types:

(a) Angiocarpic or Cleistohymenial Type:

Hymenium is enclosed in earlier stage and at maturity asci are exposed e.g. A. furfuraceus.

(b) Gymnocarpic or Gymnohymenial Type:

Hymenium is exposed in early stage e.g., A. magnificus

Liberation of Ascospores:

Each ascus has lid like operculun at its apex. Ascospores are liberated through operculum and on germination form the germ tube to form new mycelium.

Graphic Life Cycle of Ascobolus

Family―Helvellaceae:

1. The family includes the morels (spong mushroom), bell morels and saddle fungi.

2. Ascocrap (apothecium) is fairly large and clearly distinguishable into a basal stalk (strip) and upper head (pileus) region.

3. Hymenium extend over the convoluted or folded surface of pileus.

4. Sex organs are absent but stomatogamy and autogamy is common.

5. Asci are operculate.