Chytridiomycota characters, taxonomy, life cycle of synchrium and major diseases

Fundamentals of Plant Pathology

1. CHYTRIDIOMYCOTA : CHARACTERS, TAXONOMY, LIFE CYCLE OF SYNCHRIUM AND MAJOR DISEASES COURSE TEACHER: Dr. PARTHASARATHY. S Asst. Prof., (Plant Pathology) COLLEGE OF AGRICULTURAL TECHNOLOGY Affiliated to Tamil Nadu Agricultural University, Coimbatore Kullapuram,Via Vaigai dam, Theni-625 562 STUDENTS: Mr. MOHINDAR AMARNATH. R Mr. ROHITH. S

2. CHYTRIDIOMYCOTA (CHYTRIDS) The word “ chytrids” comes under Kingdom Fungi and phylum Chytridiomycota . Chytrids – Greek word - Chytridion , meaning “ little pot”. Bartnick - Garcia(1970) classified the members of Chytridiomycota as true fungi based on the presence of chitin the cell walls, aminoacid lysine synthetic pathway and storage of carbohydrates as glycogen. Barr considered chytrids as a transitional group between Protista and Fungi based on production of motile zoospores.

3. General characters: Cell wall contains chitin and glucan. Thallus is coenocytic with oval multinucleate cell or elongated hypha or a well developed mycelium. Monocentric thallus made up of single globose or oval sporangium, while polycentric consists of multisporangia on network of rhizoid termed rhizomycelium . Thallus may be epibiotic, endobiotic, interbiotic . Reproduction: Asexual: Zoospore Sexual: Resting sporangium

4. Order: Chytridiales Most of them are water or soil inhabiting Endobiotic : Synchytrium Epibiotic : Rhizophydium Thallus - Eucapic , Endogenous monocentric : Rhizophydium Halocarpic and exogenous polycentric : Synchytrium Zoospore - released through papilla : Rhizophydium pore : Synchytrium Sexual spore is resting sporangium , formed by planogametic copulation.

5. Order: Spizellomycetales Thallus – Halocarpic , monocentric endogenous and exogenous. Sexual reproduction - unknown Includes plant pathogenic genus Olipidium acts as vector for plant virus disease. Zoospore are amoeboid particularly during both swimming and encystment , Nucleus is closely associated with kinetosome from which microtubules radiate into cytoplasm.

6. Synchytrium endobioticum - Potato wart Systematic position: Phylum : Chytridiomycota Class : Chytridiomycetes Order : Chytridiales Fam : Synchytriaceae Genus : Synchytrium Species : endobioticum

7. Symptom: It occurs as an obligate parasite in the epidermal cells of potato. Early infection shows rapid cell division in the host cell division in the host tissue. The cell become enlarged due to hypertrophy and assume the shape of galls and forms warty out growth.

8. Life cycle of Synchytrium endobioticum

9. Life cycle: Asexual Reproduction Large number of uniflagellate zoospore are released from the infected portion of the tuber. After swimmimig for two hours they come to rest on the surface of potato eye or on young tuber. Uniflagellate zoospore penetrate through pores in epidermis. Flagella is shed and entered the host and takes the amoeboid shape. This increase in size and develop a golden brown thick walled prosus . The matured porus starts germinating within the daed host cells. The nucleus undergoes repeated mitotic division to form 32 nuclei.

10. Asexual Reproduction At this stage the entire multinucleate prosorus gets divided into 4-9 multinucleate chambers with help of thin hyaline walls. The nuclei keep on dividing repeatedly to form as many as 200-300 nuclei. Each of the multinucleate chambers represents a sprorangium . The group of sporangia is spore. At cleavage, nuclei surrounded by dense cytoplasmic contents develop in uninucleate and uniflagellate zoospore, if water is present they swim for some time get attached to host.

11. Sexual reproduction If there is scarcity of water the release of zoospore are delayed and uniflagellate bodies function as body. They behave as planogamets and copulation is isogamous. Karyogamy and plasmogamy take place and diploid biflagellate zygote is formed. The diploid zygote enlarge ang get enveloped in resting sporangium as rest spore or winter spore. The multinucleate protoplast of resting sporangium undergoes cleavage, from many uninucleate daughter protoplast converted in to haploid zoospore. The haploid zoospore are liberated by the rupturing of the infected host and life cylcle is repeated.

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