Sexuality in Allomyces Cystogenus

Abstract

The genus Allomyces has been subdivided by Emerson (1941) into three subgenera on the basis of the type of life cycle. Those forms in which there is an alternation of an asexual plant, bearing zo6sporangia and resistant sporangia, with a sexual one, bearing paired male and female gametangia, are included in the subgenus Euallomyces. Some isolates have repeatedly failed to produce a sexual generation. The single type of thallus in these forms corresponds in its general morphology to the asexual plant of members of the subgenus Euallomyces, i.e., bearing zo6sporangia and resistant sporangia. Such forms are segregated into a subgenus, Brachyallomyces. The third subgenus, Cystogenes, likewise, has only one generation. Its thallus is similar to that of Brachyallomyces and to the asexual plant of Euallomyces. Here, however, according to Emerson, the zo6spores released upon the germination of the resistant sporangia are biflagellate instead of uniflagellate as in Euallomyces and Brachyallomyces and, instead of developing directly into thalli, they encyst and later give rise to a tetrad of uniflagellate zo6spores each of which then develops into an asexual thallus. In the absence of cytological evidence it is not possible to interpret with certainty the Cystogenes life history. Emerson points out the close similarity between the biflagellate primary R.S. zoospores (zo6spores from the germinating resistant sporangia) and the biflagellate planozygotes of Euallomyces and, in an attempt to explain this similarity, suggests that sexual fusions may take place inside the resistant sporangia during their germination. In other words, the primary R.S. zo6spores might actually be zygotes. The production of secondary R.S. zo6spores (zo6spores produced in the cysts) in groups of four indicates that meiotic divisions may