[Biology Class Notes] on Ascocarp Pdf

Ascocarp is a kind of fungus that is also called ascoma. The plural form of ascocarp is ascomata. The Ascocarp is a fruiting structure of fungi. It belongs to the family phylum Ascomycota. If the ascocarp is in a bowl-like structure it is known as apothecia. If it takes a spherical or flask-like structure and forms an opening to release spores is known as perithecia. If the ascocarp does not have openings it is known as cleistothecia.  

Geopyxis cacabus produces the largest apothecium, which has a stalk height of 1 metre and a cup height of 50 centimetres. In ascocarp, after sexual reproduction, the vegetative filament hyphae are developed. 

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Types of Ascocarps

There are a number of fruit bodies in Ascomycota. Most of the ascomycetes are surrounded by hyphae to form an Ascocarp and Ascoma. The ascocarp is classified according to its placement, but it does not depend on the basics of taxonomy. The Types of Ascocarps are

• Apothecium

• Cleistothecium

• Gymnothecium

• Perithecium

• Pseudothecium

Apothecium 

An apothecium is a fleshy and sessile fruiting body with wide opened saucer-shaped or cup-shaped fungi. The structure of Apothecium consists of three parts namely Hymenium, excipulum, and hypothecium. Usually, asci are present in the hymenium layer and are freely exposed at maturity. For example, Dictomycetes. The fertile layer is free so many spores are dispersed widely. The edible ascocarp is Morchella. It is not a mushroom, it is favoured by gourmets. Mass of apothecia is in the form of a single large structure or cap.  Helvella and Gyromitra are in similar genera. 

Cleistothecium 

The cleistothecium is a globose structured fruity body, which means completely closed with no special opening to move outside. The ascomatal wall consists of strongly interwoven hyphae or pseudoparenchyma cells called peridium. It is covered by hyphal outgrowth called appendages. The asci are globose, tender flesh scattered throughout the interior cavity. 

Eurotium in tufts from the basal region of ascocarps is raised as Erysiphe. So, the ascocarp emerged as a hymenium enclosed round. Here spores do not release automatically. The fungi with cleistothecia fight attract animals like wild boars, it breaks open the ascocarps through this method it disseminates their spores and reaches a wide area. Cleistothecia can commonly be encountered in fungi, which will have little room for their ascocarps. These types of ascocarp are widely live under barks of trees or underground.

Gymnothecium

Like a cleistothecium, a gymnothecium pearl-shaped completely enclosed structure. It contains globose and tender asci. But, the wall of gymnothecium has a loosely packed tuft of hyphae. These are ornamented with coils or spines to attract insects. Examples of gymnothecium are Talaromyces, Gymnoascus, and dermatophyte Arthroderma. 

Perithecium

Perithecium is a flask-shaped fruity body fungus. It has an opening in the form of pore or short papilla opening (ostiole), through which ascospores can escape. The ostiolar canal is lined by the hair-like structures called periphyses. It contains cylindrical-shaped unitunicate asci, which are borne on a stipe and released from a pore.  Asci has a well-developed inner wall of perithecium that arises from a basal plectenchyma-centrum.  Perithecia are widely found in Xylaria, Nectria, members of Sphaeriales, Claviceps, Hypocreales, and Neurospora.

Pseudothecium

Pseudothecium is much similar to perithecium. Pseudothecium is a double-wall structure, which expands to take water and shoots the enclosed spores. This will happen when the pseudothecium needs to disperse spores. But the asci are not organised well inside the hymenium in Pseudothecium. An example is Apple scab and Guignardia aesculi.

Reproduction in Ascocarp

Both the sexual and asexual reproductions are common in ascocarp. The ascocarp undergoes asexual reproduction frequently and involves in the production of haploid conidiophores. This occurs during the presence of single gametes. Likewise, the ascocarp starts sexual reproduction after arising vegetative filaments called hyphae. This is common for both male and female mating strains.

During the reproduction stage, the male strain releases an antheridium, and the female strain develops an ascogonium. At the time of fertilisation, the antheridium, and ascogonium combine in plasmogamy without nuclear fusion. The dikaryon gives rise to the special dikaryotic autogenous hyphae, in which the nuclei get paired. Those nuclei are from male and female strains.

During karyogamy, the two nuclei are fused together. The fruiting body is covered with thousands of asci, which is called ascocarp. The diploid nucleus present in each ascus gives rise to the development of haploid nuclei by meiosis and spore walls are developed around each nucleus. The spores in each ascus have meiotic products that are with a single diploid nucleus. These ascospores are released, developed, and form hyphae, which are disseminated over the environment and start to develop new mycelia. 

The image shows the complete reproduction cycle of the ascocarp. The lifecycle of an ascomycete is characterized including the production of asci during the sexual phase. During this life cycle, the haploid phase is predominant.