homothallism and heterothallism in fungi

HOMOTHALLISM IN FUNGI

The condition  in which one individual originating from a single asexual spore is capable  of farming zygospore (zygote) independently is known as homothallism.  A few species of achlya such as  Achlya racemosa are homothallic.  In homothallic species two types of sex organs  i.e., anthredia and ogonia are developed on the same mycelium.

In  ACHLYA racemosa, the oogonia are developed at the tips either of short lateral hyphae or on the main hypha. The tip of the female branch swells up to form a sac like  oogonial initial . subsequently, the swollen structure is cut off by a cross wall at its base. It is the oogonium.

The anthredia are developed on thin  hyphal branches which arises from the female hypha. The tip of the anthredial hypha enlarges. A number of nuclei and some cytoplasm migrated  to the inflated tip. The swollen portion is then cut by a cross wall. It is the anthrediem.

HETROTHALLISM IN FUNGI

Hetrothallism may be defined as the condition in which zygospore ( zygote) formation takes place only when mycelia arising from sexual spores of two genetically different mating types, (+) and  the (-), are allowed to intract. The term hetrothallism was first coined by A.F. Blakeslee in 1994.

On the basis of nature of the mating types, hetrothallism may be of the following types-

·         Morphological hetrothallism :   

     Morphological hetrothallism may be defined as the condition when the morphologically different male and female sex organs are produced in two closely associated mycelia. The two sex organs or gamets are so morphologically dissimiliar that it is easier to term one of them as male and the other as female. Some of the examples of hetrothallic fungi are – Achyla ambisexualis, A, bisexualis, Phytophthora palmivora, Peronospora parasitica, etc.

·         Physiological hetrothallism : 

PPhysiological hetrothallism, the interacting thallis differ in mating type or incompatibility irrespective of the presence or absence of sex organs or gamets. This means that sexual reproduction takes place by two morphologically different hyphae. The gametangia or gametes do not show morphological differentiation but physiologically they behave differently.