Ascomycota salient features

Contents
Reproduction types and fructifications
General characteristics
Classification
Economic importance

1. ASCOMYCOTA Darshan SALIENT FEATURES OF

2. CONTENTS Introduction General characteristics Reproduction Classification Economic importance Conclusion Reference

3. INTRODUCTION Also called as “sac fungi” because their sexual spores, called ascospores are produced inside a sac or ascus Monophyletic group Largest and most diverse group of fungi Includes yeasts, molds and edible mushrooms Saprobes, parasites Economically important – baking, brewery, antibiotics production

4. GENERAL CHARACTERISTICS Ascus- a cell in which two haploid nuclei of different mating types come together and fuse to form a diploid nucleus, followed by meiosis to produce haploid sexual spores, the ascospores In many species the meiotic division is followed by single round of mitosis, leading to production of eight ascospores within each ascus In more advanced members of the group, many asci are produced within a fruiting body, the ascocarp Production of asexual spores by mitosis Asexual ascomycetes in deuteromycota

5. MORPHOLOGY Single celled, mycelial or dimorphic Cell wall composition: filamentous forms- chitin, yeasts β- 1 ,3- glucans (chitin restricted to bud scars) Dimorphism- Saprophytic molds inside host (25°C), unicellular yeasts outside hosts (37°C) Hyphae septate and perforated septa Woronin bodies – Spherical double membranous structures Plectenchyma, prosenchyma and pseudoparenchyma

6. REPRODUCTION Vegetaive Asexual Sexual Parasexual

7. VEGETATIVE REPRODUCTION Fragmentation, fission and budding

8. ASEXUAL REPRODUCTION Through formation of spores- conidia (Gr, conia = dust) Asexual, haploid spores, also known as conidiospores and mitospores Contain one nucleus and are products of mitotic cell divisions Genetically identical to the mycelium from which they originate Formed at ends of specialized hyphae, the conidiophores

9. CONIDIOMATA Conidiophores may be produced inside conidiomata known as pycnidia (sing. pycnidium) or acervuli (sing. acervulus) A pycnidium is a globose or flask-shaped pseudoparenchymatous structure that is lined on inside with conidiophores An acervulus is typically a flat or saucer- shaped bed of short conidiophores growing side by side and arising from a more or less stromatic mass of hyphae

10. ASEXUAL SPORES

11. SEXUAL REPRODUCTION Involves nuclear fusion and meiosis, occurs only in those ascomycetes which possess asci Mating behaviour may be homothallic (mycelium served from single ascospore) or heterothallic (includes outcrossing) Plasmogamy of different mating types followed by karyogamy Gametangial fusion : Two morphologically similar gametangia touch at their tips or coil around each other and fuse.The fusion cell develops into ascus

12. C O NT D . Gametangial contact : Production of morphologically differentiated uninucleate or multinucleate gametangia called antheridia and ascogonia Spermatization : Attachmentt of single detached male cell to female reproductive organ (trichogyne or somatic hypha) and empties it’s nucleus into receptive cell Somatogamy : Fusion of unspecialized somatic hyphae of two compatible mycelia with nuclei migrating to the ascogonium through septal perforations

13. DEVELOPMENT OF ASCI

14. A S CI Cleistothecium: A small hollow, more or less globose, indehiscent (prototunicate) ascocarp without an opening. The asci are scattered inside the structure. The fruit wall is called peridium which is pseudoparenchymatous Covered by hyphal outgrowths called appendages

15. C O N T D ,. Perithicium: A small rounded or flask shaped ascocarp At maturity it has a definite apical pore or opening, the ostiole The ostiolar canal is lined by slender, short, delicate, hair-like sterile growths called periphysis The perithcial wall is called peridium. It encloses a cavity lined by hymenium which consists of club shaped or cylindrical asci

16. C O N T D . Apothecium : A disc or saucer-shaped or even a cup-like structure Apothecial ascospores produce an exposed hymenium at maturity The hyphae are interwoven to form a structure called hypothecium located immediately below the hymenium Both these structures are given structural support by a fleshy part of ascocarp called exipulum

17. C O N T D . Pseudothecium : Asci are formed within locules of a preformed ascostroma Asci are bitunicate with two seperable wall layers that contribute to dehiscence Ascostromata can be multilocular or unilocular When they are unilocular it is extremely difficult to distinguish them from a true perthicium. Such unilocular ascostroma are called pseudothecium

18. CLASSIFICATION Ascomycetes are classified into 3 subphyla Pezizomycotina Sa cch a r o m yc o t ina Taphrinomycotina Discomycetes Pyrenomycetes Lorchels Caterpillar fungi 3 sub groups Archaeascomycetes (includes fission yeasts) Hemiascomycetes (possess naked) Euascomycetes

19. ECOLOGY AND SIGNIFICANCE Important decomposers in land ecosystem Fruiting bodies can be food source for insects, snails and rodents Many form mutualistic relationship with algae and cyanobacteria Symbiosis with plants- mycorrhizal ascomycetes Commensal association with plants- endophytic fungi Harmful interactions Dutch Elm disease caused by Ophiostoma ulmi has led to death of many elms in Europe Asian Cryphonectria parasitica is responsible for attacking American Chestnut and virtually eliminated the once-widespread American Chestnut

20. C O N T D . Mycotoxins produced by ergot ( Claviceps purpurea) and Aspergillus flavus are carcimogenic Aspergillus and Candida can cause infection in humans

21. CONCLUSION Most diverse and largest phylum of lingdom fungi Characterized by sexually produced ascospores contained within ascus Includes yeasts, molds and edible mushrooms Vegetative reproduction by fragmentation budding and fission Asexual reproduction is by means of conidia Sexual reproduction involves various type of somatogamy Some ascomycetes form crozier to maintain dikaryotic stage High economic importance

22. REFERENCES Alexopoulas C J and Mims C W, 2002 Introductory Mycology 4 th edition, Wiley Eastern ,New Delhi John Webster and Roland Weber, 2007. Introduction to Fungi 3 rd edition, Cambridge University Press David Moore, Geoffrey D. Robson, Anthony P. J. Trinci (2011) 21st Century Guidebook to Fungi . Cambridge University Press. B.R.Varishta,A.K Sinha, 2011. Botany for degree students: Fungi. S Chand https://cals.arizona.edu/classes/plp427L/lab8.html https://study.com/academy/lesson/the-economic-importance-of-ascomycota.html www.wikipedia.com