Introductory mycology alexopoulos citation

In Cystogenes life cycle the resting sporangia (from the sporophyte) give rise to biflagellated, bi-nucleated zoospores that will encyst, undergo meiosis, and germinate to yield motile gametes. The resting sporangia undergo meiosis at germination and give rise to haploid zoospores that will germinate and grow into gametophytes. The thin-walled zoosporangia give rise to motile zoospores that germinate and grow into another sporophyte. It grows into a dichotomously branched sporophyte, which forms two types of sporangia: thin-walled zoosporangia that may be colorless or orange and thick-walled resting sporangia that are reddish-brown due to the presence of melanin pigments. The resulting zygote is initially biflagellate, but it soon encysts and germinates. The plasma membranes fuse to form a binucleate cell with nuclear fusion quickly following. Fertilization takes place when two gametes contact one another. Fertilization of female gametes by male gametes appears to be near 100% efficient. Female gametes are sluggish and stay close to the female gametangia, which sets up a strong concentration gradient of sirenin. Male gametes produce a pheromone called parisin. Female gametangia and gametes release a pheromone called sirenin that attracts the male gametes.

Both male and female gametangia release motile gametes, but the male gametes are smaller and orange. Formation of male gametes is faster than of female gametes. Gametophytes produce colorless female gametangia and orange male gametangia the orange coloration is transferred to the male gametes and is due to the presence of gamma carotenoid.

In this life cycle, the two stages are indistinguishable until reproductive organs are formed. The Euallomyces life cycle is an anisogamous alternation of generations between a haploid gametophyte and a diploid sporophyte. Euallomyces and Brachyallomyces are known to be classified as polyphyletic but Cystogenes is monophyletic. There are three distinct life cycles in Allomyces, and some authors delineate the subgenera Euallomyces, Cystogenes, and Brachyallomyces based on the life cycles while others do not. Note the orange-brown zoosporangia and resting sporangia at the terminals of the branches. Zoomed out view of a mature thallus of Allomyces strain WJD103.

Introductory mycology alexopoulos citation