7th Lab Practical Mycology 2021 Phylum: Chytridiomycota (Zoosporic Fungi) (Zoosporic Fungi) Kingdom: Fungi Phylum: Chytridiomycota Kingdom: Straminipila Phylum: Oomycota Protista Phylum: Myxomycota Phylum: Chytridiomycota 1. True Fungi. 2. The most primitive fungi. 3. Aquatic, flagellated fungi. 4. Branching hyphae. 5. Cell wall composed of Chitin. 6. Produce motile spores called zoospores. 7. Remember: these are the only fungi with flagellated cells. 8. Some are saprobes, while others parasitize protists, plants and animals. Main characteristics: Somatic stage Coenocytic hyphae with globular, ovoid or well-develop mycelium. Mostly haploid, but some species are diploid. Cell wall are mainly chitin and glucan. Reproduction Asexual reproduction by production of single posterior whiplash zoospore in ZOOsporangium Sexual reproduction by formation of resting sexual spore by mean of planogametic copulation. Classification 123 genera, 900 species in 5 orders: • Chytridiales - Spizellomycetales • Blastocladiales - Monoblepharidales • Neocallimasticales 1 7th Lab Practical Mycology 2021 Zoospore • Microscopic (2-14 x 2-6 micron), uninucleate, unicellular, flagellated spore lacking a cell wall. • Formed in a zoosporangium by a process involving mitosis and cytoplasmic cleavage. • Zoospores rely on endogenous energy reserves. Flagella: 0.25 microns wide, up to 50 microns long. One to many flagella depending on the taxonomic group. May have only whiplash, whiplash + tinsel, or only tinsel, flagellum may be unequal in length (= heterokont). Zoosporangium • A typically multinucleate structure that produces zoospores by a process called zoosporogenesis. • Zoosporogenesis includes mitosis and cleavage of zoospores from zoosporangium cytoplasm. • Zoospores release through one of several methods: - Breakdown of zoosporangial wall. - Opening of cap-like cover called operculum. - Discharge papillae plugged with gelatinous material. Thallus types relative to substrate • Endobiotic: Thallus produced inside host or substrate. • Epibiotic Thallus produced outside host or substrate; rhizoides formed from thallus to absorb substrate. 2 7th Lab Practical Mycology 2021 Endobiotic Epibiotic Resting zoosporangium in zoosporangium during releasing of Resting zoosporangium in Allomyces zoospore Flagellate zoospore Sporophyte of Allomyces Male and femal gamantagium of Allomyces in Agar culture 3 7th Lab Practical Mycology 2021 Asexual Reproduction • Uniflagellate zoospore One whiplash flagellum inserted in posterior part of zoospore. • Zoospores formed in zoosporangia and released through an operculum or discharge papilla Sexual Reproduction • Plasmogamy and karyogamy results in formation of resting sporangium. Thickened, often pigmented and/or ornamented wall. • Germination of resting sporangium occurs after meiosis by cleavage of cytoplasm into zoospores. 4 7th Lab Practical Mycology 2021 Synchytrium SPP. ◆ S. endobioticum is a parasitic genus causing black wart disease on potato. ◆ Characterized by enlargement of surface cell (hypertrophy) and increase numbers of cell (hyperplasia). Classification • Kingdom : Fungi • Phylum : Chytridiomycota • Order : Chytridiales • Family : Synchytriaceae • Genus : Synchytrium • Species : endobioticum • Common names: Black wart of potato Synchytrium Endobioticum • Does not produce hyphae and is an obligate, endobiotic parasite. • It is a long-cycled chytrid characterized by a short-lived swarm (summer) sporangial stage resulting from host infection by uniflagellate zoospores and a resting (winter) sporangial stage resulting from host infection by conjugated zoospores (biflagellate zygotes). • Both sporangial types germinate to release 200-300 zoospores, which are pear-shaped infective units and motile by means of a posterior flagellum. Resting sporangia are golden brown and spheroidal. • The resting sporangium wall has prominent exterior ridges and contains chitin. Winter (resting)(left) and summer (right)sporangia of Synchytrium endobioticum 5 7th Lab Practical Mycology 2021 Symptoms: Potato wart symptoms can be found on all underground plant parts except roots. 1- Stem – Galls form at the base of the stem; initially white, but turning black when decaying; may be as small as a pin or as large as a fist; surface is rough-warty in appearance. 2- Tubers - Eyes develop cauliflower-like swellings; when formed underground, they are the same color as the potato skin, darkening with age, or green if exposed to light. Typical warts are soft and pulpy and easier to cut than a healthy tuber. 3- Stolons - Symptoms similar to tubers. 4- Aerial buds - Small greenish warts form in the position of the aerial buds at the stem bases. Black wart disease caused by S. endobioticum Cross section of a potato infected with black scab (Synchytrium endobioticum) fungus. The cells balloon out and later turn into sporangia (pink patches), which contain numerous spores. 6 7th Lab Practical Mycology 2021 Disease cycle: 1. In the spring, resting sporangia in decaying warts and soil germinate to release haploid (uninucleate) zoospores. 2. These zoospores migrate in soil water for a limited distance (50 mm or less) via a single flagellum to arrive at epidermal cells of meristematic tissues of growing points, buds, stolon tips, or young leaf primordia. 3. Zoospores are short-lived and must encyst and infect susceptible host tissue within 1-2 hr after their formation. 4. After infection by zoospores, potato host cells greatly enlarge and haploid sori form inside the host cells while neighboring host cells begin to proliferate, resulting in the characteristic warty galls and the increased presence of the meristematic tissue that provides new infection courts for the fungus. 5. Each sorus contains 1 to 9 summer sporangia, which in turn germinate to produce new haploid zoospores which reinfect susceptible tissue (i.e., a secondary disease cycle). 6. zoospores also may conjugate to form uninucleate, diploid, biflagellate zygotes which infect the host tissue to form resting sporangia. 7. Following infection by zygotes, the host cell in which resting sporangia form does not swell but divides to form galls. 8. The host cell wall remains closely attached and forms an outer layer to the resistant, thick- walled resting (winter) sporangium. As these galls decay and disintegrate, they release the thick-walled resting sporangia into the soil environment. Resting sporangia are endogenously dormant and can remain viable for 40 to 50 years at depths of up to 50 cm (20 inches) in the soil profile. 9. Resting sporangia survive passage through the digestive system of animals fed infected potatoes, and contaminated manure also can disperse inoculum. Earthworms have also been found to serve as means of inoculum dispersal, and resting sporangia can be dispersed by wind-blown soil or by flowing surface water. 7 7th Lab Practical Mycology 2021 Synchytrium life cycle 8 .