Fragmentation Zoospores and Conidia
It is that type of asexual reproduction in which the parental body breaks into two or more fragments either by wave action (e.g. sponges) or by death and decay of old parts. Each body fragment develops into an organism. It is found in some flat worms (Microstomum), sea anemones among coelenterates, and echinoderms. In starfish, even one arm with a part of central disc can develop into whole animal.
(a) There is no need of sexual partners.
(b) Rapid rate of reproduction.
(a) No chance of new combinations of genes and variations. So individuals may not be able to adapt to changing environment.
(b) It generally leads to overcrowding and struggle for existence.
Members of kingdom fungi and algae reproduce through special asexual reproductive structures called zoospores (Fig. 1.12). These are flagellated, motile naked protoplasmic bodies. Zoospores are produced in zoosporangium.
Zoospores may be biflagellate (e.g., Ectocarpus), quadriflagellate (e.g., Ulothrix) or multiflagellate (e.g., Oedogonium). They may be uninucleate (e.g., Ulothrix) or multinucleate called synzoospores.
These are non-motile spores produced exogenously by constriction at the tips of special hyphal branches known as conidiophores. The conidiophores may be branched or unbranched. They produce conidia singly as in Phytophthora or in chains as in Aspergillus and Penicillium (Fig. 1.13).
Conidia may be unicellular (e.g., Penicillium) or multicellular e.g., in Cercospora, Alternaria. The conidia may germinate directly to produce mycelium or may produce zoospores which upon germination produce mycelium. The latter type of conidia are called corudiosporangia (e.g.. Albugo).
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