What is the Difference Between Oomycetes and Zygomycetes

The main difference between Oomycetes and Zygomycetes is that Oomycetes produce gametangia differentiated into antheridia and oogonia as a result of the sexual process whereas Zygomycetes produce zygosporangia, which is heterokaryotic. Furthermore, Oomycetes are often known as water molds as this type of fungi prefer water while Zygomycetes are a type of terrestrial fungi living in soil or on decaying plant or animal material.

Oomycetes and Zygomycetes are two classes of fungi that produce hyphae. They reproduce both sexually and asexually by the formation of spores.

Key Areas Covered

1. What are Oomycetes
     – Definition, Characteristics, Classification
2. What are Zygomycetes
     – Definition, Characteristics, Classification
3. What are the Similarities Between Oomycetes and Zygomycetes
     – Outline of Common Features
4. What is the Difference Between Oomycetes and Zygomycetes
     – Comparison of Key Differences

Key Terms

Asexual Spores, Gametangia, Mycelium, Oomycetes, Sexual Spores, Zygomycetes

What are Oomycetes

Oomycetes are a class of fungi characterized by the presence of oogamous type of sexual reproduction and asexual reproduction, which occurs by producing biflagellate zoospores, which lack a cell wall. They represent an algae-like fungal group, which can be either aquatic, free-living or parasitic. Also, many terrestrial Oomycetes fungi form downy mildew diseases on higher plants. Additionally, this class includes primitive forms of unicellular fungi as well as advanced forms of fungi with a well-developed, branched, filamentous, and coenocytic mycelium. 

Figure 1: Pythium – Peronosporales

During sexual reproduction, Oomycetes produce differentiated sex organs known as antheridia and oogonia. Here, meiosis occurs in the gametangia known as gametangial-meiosis, but not in the zygote. Therefore, their vegetative thallus is diploid. Also, asexual spores are produced inside sporangia.

What is Zygomycetes

Zygomycetes are another class of terrestrial fungi characterized by the presence of thick-walled, resting spores known as zygospores. These zygospores are formed by the fusion of protoplasts of two equal or unequal gametangia. The terrestrial members of Zygomycetes are mainly saprotrophs and some are coprophilous, growing on dung. Parasitic species including pin molds infect other fungi, insects or protozoa. Some of them are obligate parasites on other members of Zygomycetes. In higher plants, they are facultative weak parasites.

Figure 2: Pin Mold on Peach

Generally, the fungal hyphae of Zygomycetes are non-septate but, old hyphae may contain septa. This class forms septa while forming reproductive structures and sealing off injuries. One of the main characteristic features of Zygomycetes is the absence of motile cells in the life cycle. The asexual spores known as sporangiospores or mitospores are produced inside sporangia. Furthermore, Zygomycetes has economic importance as they are used to ferment food items and to produce enzymes, acids, etc.

Similarities Between Oomycetes and Zygomycetes

• Oomycetes and Zygomycetes are two classes of filamentous fungi.
• They are either saprotrophic or parasitic.
• Usually, their hyphae are non-septate. But, the hyphae producing gametes form septa.
• Moreover, their hyphae are coenocytic, which means they are made up of multinucleated cells.
• Besides, their cell wall is not made up of chitin.
• Also, they reproduce sexually and asexually by the production of spores.
• And, both groups produce chlamydospores as a form of asexual spores.
• Furthermore, their sexual spores are mainly a form of resting spores.

Difference Between Oomycetes and Zygomycetes

Definition

Oomycetes refer to a subclass of parasitic of saprophytic fungi (class Phycomycetes) that includes water molds, white rusts, and downy mildew while zygomycetes refer to a wide variety of common fungi in which sexual reproduction is by the formation of zygospores. Thus, this is the main difference between Oomycetes and Zygomycetes.

Habitat

Oomycetes are often known as water molds as this type of fungi prefer water while Zygomycetes are a type of terrestrial fungi living in soil or on decaying plant or animal material. Hence, this is another difference between Oomycetes and Zygomycetes.

Organization

Also, one other difference between Oomycetes and Zygomycetes is that Oomycetes can be either unicellular or filamentous while Zygomycetes are filamentous.

Cell Wall

Furthermore, the cell wall of Oomycetes is made up of cellulose while the cell wall of zygomycetes is made up of chitosan.

Vegetative State

Besides, the vegetative state of Oomycetes contains diploid nuclei while the vegetative state of Zygomycetes contains haploid or dikaryotic nuclei. So, this is also a difference between Oomycetes and Zygomycetes.

Sporangia

Moreover, Oomycetes do not produce sporangia and their asexual spores are formed inside conidia while Zygomycetes produce sporangia.

Asexual Reproduction

The two forms of asexual spores produced by Oomycetes are zoospores and chlamydospores while the two forms of sexual spores produced by Zygomycetes are mitospores and chlamydospores.

Type of Gametangia

Additionally, Oomycetes produce gametangia differentiated into antheridia and oogonia as a result of the sexual process whereas Zygomycetes produce zygosporangia, which is heterokaryotic. So, this is also a difference between Oomycetes and Zygomycetes.

Sexual Reproduction

The sexual reproduction of Oomycetes occurs through the production of oospores while the sexual reproduction of Zygomycetes occurs through the production of zygospores.

Sexual Spores

Sexual spores is another difference between Oomycetes and Zygomycetes. The sexual spores of Oomycetes (Oospores) are biflagellate and lack a cell wall while the sexual spores of Zygomycetes (zygospores) are non-motile and have a thick cell wall. 

Meiosis

Meiosis of Oomycetes occurs in the gametangia not, in the zygote while meiosis of Zygomycetes occurs in the zygosporangium after the formation of zygote.

Diseases

While oomycetes are plant pathogens and they can cause disease in fish while Zygomycetes are parasitic on plants, insects, and small animals.

Classification

The six orders of Oomycetes are Saprolegniales, Leptomitales, Rhipidiales, Albuginales, Peronosporales, and Lagenidiales while the four orders of Zygomycetes are Mucoromycotina, Kickxellomycotina, Entomophthoromycotina, and Zoopagomycotina.

Conclusion

Oomycetes are a class of water-preferring, filamentous, aseptic fungi. They produce zoospores as their asexual spores and oospores as sexual spores. In comparison, Zygomycetes are another class of terrestrial fungi that is also filamentous and aseptic. They produce mitospores as asexual spores and zygospores as sexual spores. Additionally, the vegetative form of Oomycetes is diploid while that of Zygomycetes is haploid or dikaryotic. Significantly, Oomycetes produce sexually differentiated gametangia, which produce gametes while Zygomycetes produce zygosporangia, which are heterokaryotic. Therefore, the main difference between Oomycetes and Zygomycetes is the type of gametangia produced during sexual reproduction.  

Reference:

1. Garg, M. “Oomycetes: Features and Significance | Phycomycotina.” Biology Discussion, 16 Sept. 2016, Available Here.
2. Kritartha, S. “Zygomycetes: Features and Classification | Fungi.” Biology Discussion, 28 Nov. 2016, Available Here.

Image Courtesy:

1. “Pythium (257 23)” By Doc. RNDr. Josef Reischig, CSc. – Author’s archive (CC BY-SA 3.0) via Commons Wikimedia  
2. “PinMould on Peach HighMag Scale” By Zephyris – Own work (CC BY-SA 3.0) via Commons Wikimedia