Zoospores secondary type are liberated from vesicles

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Zoospores (secondary type) are liberated from vesicles formed by multinucleate sporangia Fig. 18: Different Sporangia in the Pythiaceae : A – Filamentous Sporangia, B – Globose/Oval Sporangia, C – Lobulated Sporangia
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Continuation The liberated zoospores lost their flagella and encyst before germinating by germ-tube to produce the thallus Sexual reproduction in the Pythiaceae starts with the development of gametangia. (i) Contact for the purpose of copulation may be monoclinous or diclinous depending on species sexuality. (ii) Matured oogonium differentiates into a central oosphere enveloped by the periplasm , and undergoes meiosis to produce haploid egg cell. (iii) the antheridium multinuclei degenerates to a single nucleus that undergoes meiotic division. (iv) After fertilization oospore is formed and may also act as a resting spore before
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Fig. 19: Atypical life-cycle of Pythiaceae ( Pythium debaryanum ) (v) Germination of the oospore is influenced by environmental temperature and can germinate either by germ tube (directly) at optimum temperature (20 0 C) or by vesicle (indirectly at low temperature (10 0 C – 17 0 C)
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Continuation Pythium spp.: Damping-off (tobacco, tomato, castor, chilli, etc) Rot (ginger, pawpaw, curcurbits, tumeric, hibiscus, etc) Phytophthora spp.: Canker disease Pod rot Leaf fall Blight
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EXERCISES : 1. Label when necessary and describe the oogonial, thallus and copulation variations in the Figures on the right. 2. What are the differences in the life cycle process of both the Sprolegniales and the Peronosporales 3. State the differences between the Chytridiomycetes and Oomycetes based on (a) zoopore habit, (b) zoospore flagella, (c) sporangial structure, (d) sexuality, (e) vegetative body
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Continuation 4. In a tabular form state the differences between Pythium , Peronospora and Albugo. (reading material : B.R.Vashishta and Dr. A.K. Sinha (Revised Edition -2011). 782pp. S.Chang and Company PVT Ltd, New Delhi). 5. Which group of Fungi are referred to by these common names: cellular slime mold, acellular slime molds, egg-fungi, anaerobic slime molds. 6. Mention and describe hypha and mycelium modifications in fungi. 7. Describe the life cycle of Albugo candida, Allomyces arbuscula, Pythium debaryanum.
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Continuation 8. What is the meaning of the following terms; (a) ooplanogametic copulation, (b) amphigynous, (c) coenocytic hypha, (d) planetism, (e) dimorphism, (f) Apophysis, (g) Interbiotic, (h) rhizomycelium, (i) gametangial proliferation. 9. State the economic importance of the DIVISION –Amastigomycotina 10. The life cycle diagrams (a, b, c, d) below belongs to which group of fungi
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a b
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c d
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  • Fall '19
  • Spore, Slime mold, multinucleate sporangia

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