MYCOLOGY- CHYTRIDIMYCOTA

CLASS CHYTRIDIMYCETES

The  lowest  fungi  ever  studied  are  the  chytrids  of  the  family  Chytridiaceae  and  order Chytridiales. These are fungi that produce motile spores called zoospores (planogametes). The zoospores have a single posterior whip-lash like flagellum. The coenocytic thallus is made up of  simple  hyphae  and  the  thallus  is  well  developed.  The  conjugating  zoospores  soon develop/convert into a resting sporangium.

HABITAT:  They  are  prevalently  aquatic  but  some  are  found  in  soil,  while  a  good  number are  parasitic  in  the  tissue  of  angiosperms.  They  can  be  collected  and  cultivated  easily  using baits like fruits, pollen grain, boiled grass blades, egg albumen, cellophane, nectars of flowers, petals, insect excuvia, dead insects etc. Colonies are often inside or outside the bait

SOMATIC STRUCTURES OF CHYTRIDS 

In every primitive chytrids, the somatic structures are unicellular and holocarpic in fungi with holocarpic  somatic  structures,  the  same  somatic  structure  serves  for  both  vegetable  and reproductive purposes. Such fungi do not have respectable mycellium. In slightly higher ones, there  are  few  rhizoids  for  anchorage  and  nutrition.  The  sporogenous  part  of  the  thallus  is separated from the rest by a septum. On  the  evolutionary  trend  of  chytrids  the  somatic  structures  range  from  simple holocarpic  to  eucarpic.  It  also  ranges  from  simple  cell  to  simple  rhizoids,  to  complex rhyziods  and  extensive 

rhizomycellium.  The  mode  of  reproduction  ranges  from isogamous, ansogamous, gamentagial copulation to somatogamy as in N. ramosa.  Some  higher  chytrids  have  branches  of  rhizomycellium  and  there  are  some  with  well developed hyphae with pseudo-septa

Asexual reproduction in chytrids  This is by means of sporangia. The sporangium is initially filled with densely fluid in form of protoplasm  followed  by  cleavage.  The  protoplasm  becomes  separated  and  surrounds  the nucleus

ASEXUAL REPRODUCTION IN CHYTRIDS 

The zoospores can be released in a number of ways; 

1.  If the chytrid is inoperculate, the zoosporangium breaks. 

2.  If it is operculate, the operculum opens and the chytrids escape from the operculum.  The  zoospores  thus  liberated  would  swim  for  a  little  while  and  encyst,  loose  their  flagellum and  secretes  a  cell  wall  round  themselves.  After  some  time,  the  zoospores  geminate  as  their ancestors.  

SEXUAL REPRODUCTION IN CHYTIDS 

Sexual reproduction in chytrids is more complex and can take any of the following forms:

1.Planogametic copulation: Two swimming gametes conjugate and form a zygote. When the  two  swimming  gametes  are  equal  in  size,  the  copulation  is  said  to  be  isogamous. Quite  often  the  gametes  may  be  unequal  thus  called  planogametes.  The  conjugation  of two  unequal  gametes  leads  to  the  formation  of  a  motile  gamete  which  later  looses  the flagella  and  becomes  resting.  It  is  then  called  anisogamous.  The  non-motile  gamete  is usually  the  female,  larger  and  sedentary  while  the  motile  gamete  is  the  male.  The  non- motile female gametes are known as oogonia and the males are the antheridia 

2.Gamentagial  copulation: The body  of the  gamentagial of two  gametes  fuses to form a zygote.  The  entire  protoplasm  of  1  gamentaguim  fuses  with  another.  The  two  fuse together after which cleavage occurs and spores are formed.

3.Somatogamy:  The  gametes pass from the rhizoid form to form a zygote which forms a resting  gamete (spore) which  later  germinate and later release spores.  Fungi in the class  Chytridiomycetes  are  classified  into  4  orders  which  include;
(1).Chytridiales, 
(2) Blastodiales, 
(3) Monoble pharidiales  
(4) Harpochytridiales