Gradual degeneration of sex in fungi

 Gradual degeneration of sex in fungi.

Degeneration means the functional or structural simplification of reproduction system and reproduction mechanism. The evolution of sex in fungi is completely different and doesent resemble progressive line of evolution as in the other group of living organisms. In lower groups of fungi, the sexual reproduction takes place through

isogamy, anisogamy and oogamy where gametes are developed in gametangia

and union of gametes, results in the formation of zygote. But in higher fungi, a

progassive simplification of process is observed in different direction. The overall

accounts of generation of sex organs are as follows-----

(1) Degeneration in sexual gamete: The most primitive type of reproduction in

fungi is isogamous, noted in the members of phycomycetes and oogamous type

of reproduction is noted in the members of oomycetes like Phytophthora ,

Pythium ect. Upto this stage, the evolution rum in progressive lime but

degeneration starts.

(2) Degeneration in process of oogamy: In zygomycetes, the method of reproduction

follows the gradual decrease in complexity. In zygomycetes, generally sexual

reproduction takes place by gametangial copulation. This phenomenon is isogamy so

far as the gametes are concerned but are resemble with oogamy of saproligniales

and perenosporales. In this case, the gametangia fuse together and oogamous type

of reproduction have been degenerated.

(3) Degeneration in gamete producing mycelia structure: Next evolutionary step

observed in the members of Ascomycotina. A great diversity is observed in respect of

degeneration in sex in the members of Ascomycotina.

In Ascobolus, antheridium & archegonium are farmed which

united by plasmogamy and karyogamy. Plasmogamy and karyogamy takes place in

young ascus and two processes are separated by extrinsic development of Ascogenus

hyphae. As both male and female organs are preseil and functional, it is considered

as oogamy . In this case, antheridium and antheridium nuclei migrate in oogonial

cavity.

In some cases, fusion between male gamete & female gamete takes

place with a trichogyni where no fusion sex organs takes place.

Example: Mycosphaerella tulipiferae

The typical method of sexual reproduction of Ascomycetes is

characterized by the reproduction method of Pyronema confluence. Here,

ascogonium and antheridium are well developed and union between the sex organs

takes place through plasmogamy. After associstion between the opposite nuclei in

the oogonium, ascogenous hyphae develops on the outer wall, containing a pair of

opposite nuclei. After crozier formation, following mitotic division of each nucleus an

ascus is developed in the middle cell. Farther mitotic and meiotic divisions result

eight microspores in an ascus.

In Aspergilous herbariorum, the antheridium is present

but function less. The antheridium coils round the oogonial base but to establish

contacts with the receptive organs i.e., the trichogyni. Thus oogonium with certain

asexual spores instead of antheridium. Similar pattern is also noted in

Humoriaumoria granulate where oogonium fuses with ordinary vegetative mycelium.

Finally in Aspergilous equinis, it is observed a complete absence of any sexual act and

life processes involved a haploid phase only which is known as apomixes.

(4)Degeneration in karyotic condition of mycelium: In Basidiomycotina, degenerating in

karyotic condition of mycelia is noted. In Basidiomycotina, sexual reproduction takes

between hyphae of opposite mating type leading to plasmogamy and dikaryotiation.

Dikaryotic takes persist far different periods of time and then karyogamy takes place

in the young basidium. There fare, monokaryotic mycelium functions as sex organs.

Through the members of Basidomycotina show simplicity in sex organs, they still

exhibit gradual deganation among themselves.

In Agaricus Polyporus monokaryotic mycelium is well developed

and extensively branched. In Ustilago zeae , the monokaryotic stage is not

extensively developed where as in Ustilago sagetum, the basidial cells develop

infection thread and dikaryotic condition are established between the infection

thread of opposite mating type.

So, to trace the gradual degeneration, we should note the degeneration of sex

structure. On the basis of discursion, it is better to designate the phenomenon of

simplification of sex organs rather than degeneration of sex because here only the

structure of sex organ degenerated but the process of reproduction become more

complex.