Saprolegnia and Phytophthora: Oomycetes or Water Molds

Updated on June 6, 2018
AliciaC profile image

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about animals and plants.

Water mold growing on a dead mayfly larva
Water mold growing on a dead mayfly larva | Source

The Oomycetes or Water Molds

Oomycetes or water molds are interesting organisms that share some features with fungi. They often grow in aquatic and damp environments but are also found in drier areas. Saprolegnia and Phytophthora are important examples of the group. Saprolegnia is a common cause of the so-called fungal infections experienced by freshwater fish. Phytophthora was responsible for the devastating Irish potato famine of the nineteenth century and is also a pathogen of other plants.

Oomycetes (pronounced oh-oh-my-see-tees) were once classified as fungi because their body and behaviour have similarities to these organisms. They grow as branching filaments known as hyphae, as fungi do. They also absorb nutrients through the walls of the hyphae and reproduce by spores. Biologists have discovered that there are some important differences between oomycetes and fungi, however.

Though biologists agree that oomycetes shouldn't be classified in the same group as fungi, there isn't yet a consensus about how they should be classified taxonomically. They are thought to be related to the Chromista, a group that contains several types of algae. These algae share certain features with oomycetes that fungi lack.

Saprolegnia on sesame seeds in water
Saprolegnia on sesame seeds in water | Source

Saprolegnia Hyphae and Nutrition

The body of Saprolegnia consists of branching hyphae that extend through its food source. The walls of the hyphae are made of cellulose. The hyphae generally lack cross-walls, except at the base of the reproductive structures, and contain multiple nuclei.

Fungi very often (but not always) have cross-walls known as septa in their hyphae. These divide the hyphae into cells, each with its own nucleus or nuclei. The walls of fungal hyphae are made primarily of chitin and don't contain cellulose.

The various species of Saprolegnia are either saprophytes or parasites. Saprophytes feed on dead bodies or decaying material that was once living. Saprolegnia hyphae release digestive enzymes into their environment in order to convert dead or decaying material into a suitable form for absorption.

Parasitic forms of Saprolegnia are found in living organisms. They obtain their food by digesting materials, cells, and tissues in their environment and then absorbing the products. They are sometimes classified as necrotrophs because they kill living cells and extract nutrients from them.

Saprolegnia
Saprolegnia | Source

The Saprolegnia photographs in this article show real organisms or structures made by them as viewed under a light microscope. The colour of the photos has been digitally adjusted to make the parts of the organisms easier to see, however. The photo above shows a hypha (item C) and reproductive structures.

Asexual Reproduction

Some of the hyphal branches of Saprolegnia develop a zoosporangium at their tip, as shown in item B in the photo above. Item D is the upper wall of the zoosporangium, or the septum. The zoosporangium produces spores by asexual reproduction. Each spore is known as a zoospore and is motile. When a zoospore is released from the zoosporangium and germinates, it produces the first hypha of a new individual.

Each zoospore has two flagella, which are of different types. Flagella are long and thin extensions that are often found on motile cells. As flagella move, they propel a cell through a liquid. One of Saprolegnia's two flagella is known as a whiplash flagellum and the other as a tinsel flagellum. Each points in a different direction. Hair-like extensions surround the tinsel flagellum.

The two types of flagella possessed by a zoospore can be seen in the illustration of the Phytophthora infestans life cycle shown below. The nature of the flagella supports a link to the Chromista. Fungal flagella are of the whiplash type while the flagella of the Chromista are the same as those of oomycetes. The video below shows zoospores being released from a Saprolegnia zoosporangium and then swimming away. Their thin flagella can't be seen, however.

Sexual Reproduction in Saprolegnia

Oogonium

Saprolegnia also reproduces sexually. The female organ is called an oogonium and is item F in the photo above. The oogonium produces large oospheres or eggs. These are said to be haploid (n) because their nucleus has half the number of chromosomes present in the nuclei of the hyphae. The hyphal nuclei have double the number of chromosomes found in the oospheres—or a double set—and are said to be diploid (2n). The situation is somewhat similar to a woman's eggs (haploid) having half the number of chromosomes as her body cells (diploid).

Unlike the case in oomycetes, the hyphae of fungi contain haploid nuclei. This is yet another significant difference between fungi and oomycetes.

Antheridium

The male organ is known as the antheridium. It's smaller than the oogonium. The antheridium of some organisms contains sperm cells, each containing a haploid nucleus. In Saprolegnia, the haploid nuclei are present in the antheridium, but sperm cells aren't made.

Fertilization

The stalk bearing the antheridium grows, causing the antheridium to come into contact with the side of the oogonium. The antheridium then creates a short tube that pierces the oogonium. A male nucleus travels along the tube and fuses with the female nucleus in an oosphere. The resulting diploid structure is known as an oospore or a zygote (item A in the illustration above). The oospore is released into the environment and produces a new Saprolegnia.

An oogonium containing oospheres
An oogonium containing oospheres | Source

Items A and B in the photo above are immature oogonia of Saprolegnia. Item C is a mature oogonium and item D is an oosphere or egg.

Saprolegniasis in Fish

Saprolegnia can cause disease in freshwater fish and their eggs. It can also infect amphibians and their eggs as well as crustaceans. Saprolegnia parasitica is the chief species that affects fish. It causes an infection known as saprolegniasis.

Saprolegniasis may be a special problem in fish farms. The Fluffy Fish organization carries out scientific research into the disease in the UK. According to the organization's website, the Scottish salmon farming industry experiences a financial loss of five million pounds a year due to saprolegniasis. Wild and aquarium fish may also be infected by a species of Saprolegnia. Chemical treatments for the disease exist. These may be helpful, but this isn't always the case.

The parasite starts by infecting the outer layer of a fish. A mass of fine white threads may appear on the scales of the body and the fins. The mass may resemble cotton wool. The hyphae of the parasite may extend into the gills or muscles of the fish and also enter its blood vessels, which can cause serious effects.

Cysts are produced in some stages of the reproductive cycle of oomycetes. A cyst is a thick-walled and dormant structure that protects its internal contents from harmful environmental conditions. Researchers have found that a primary cyst in Saprolegnia parasitica has hook-like projections on its surface. These may help it to attach to fish that are passing by.

Phytophthora: The Plant Destroyer

The various species of Phytophthora can cause serious problems for plant growers. They can infect many different kinds of plants. Economic losses caused by the genus may be severe. The name "Phytophthora" is derived from two Greek words: phyto, meaning plant, and phthora, meaning destroyer.

As in Saprolegnia, the body of Phytophthora consists of branching hyphae. The hyphae have similar features to those of Saprolegnia and obtain nutrients in the same way. The life cycle of Phytophthora resembles that of Saprolegnia but has some slightly different features.

Life cycle of Phytophthora infestans on potato
Life cycle of Phytophthora infestans on potato | Source

Reproduction in Phytophthora infestans

Asexual Reproduction

Like Saprolegnia, Phytophthora reproduces asexually by producing a zoosporangium containing zoospores. Also like Saprolegnia, the zoospores have a whiplash flagellum and a tinsel one. The zoosporangium or its precursor may produce a new organism directly instead of producing zoospores that do this job, however, as shown in the illustration above. In this case, the sporangium may be called a conidium.

Sexual Reproduction

An immature Phytophthora oogonium contains multiple nuclei, but at maturity only one oosphere containing a single nucleus is present. Similarly, an immature antheridium contains multiple nuclei, but by the time it reaches maturity it has only one nucleus. During sexual reproduction, an oogonium grows into and through an antheridium, enabling the female nucleus and the male nucleus to meet.

Another difference between sexual reproduction in Saprolegnia and Phytophthora exists. In order for sexual reproduction to occur in Phytophthora infestans, two mating types must meet. These are known as A1 and A2 organisms.

Late Blight in Potatoes

Phytophthora infestans causes the disease known as late blight or potato blight. The organism infects the stems and leaves of the potato plant, producing dark lesions. White threads may be seen on the undersurface of the leaves. The infection may kill the plant.

The pathogen sometimes reaches the tubers of the potato plant, which are the part that we eat. The inside of the potatoes turns brown. The brown colour appears on the outer layer of a potato first and gradually moves inward, making the tuber inedible. The pathogen can spread through the potato even after it's gathered from the field. An additional problem is that the pathogen makes the potato plant susceptible to infection by other organisms. These may cause further damage to the tubers while they are in the field or while they are in storage.

Late blight was given its name because it appeared later in the year than early blight. Early blight is caused by a fungus and can also destroy potatoes. Despite their names, early and late blight may occur at the same time of year.

In one week during the summer of 1846, this disease wiped out almost the entire potato crop of Ireland, a crop which was the primary food of the poor at that time. Nearly a million Irish died in the Great Famine.

— University of California Museum of Paleontology (with reference to late blight of potato)
A potato infected by Phytophthora infestans
A potato infected by Phytophthora infestans | Source

The Irish Potato Famine

Phytophthora infestans can be a serious problem for both potato and tomato plants today. Nevertheless, it no longer produces devastation resembling that of the Irish potato famine of the mid nineteenth-century. The huge number of deaths (around a million) and the massive emigration (around one-and-a-half-million people) that occurred as a result of the famine affected both Ireland and the world.

As a result of studying herbarium specimens that were collected in the past, researchers have discovered that the famine was caused by a strain of Phytophthora infestans that (apparently) no longer exists. New strains appear to have arisen as new varieties of potatoes appeared and the famine strain seems to have disappeared at around the same time.

Researchers who have examined the genome of the famine strain say that it doesn't appear to be inherently more virulent than today's strains. They suspect that the two major conditions that caused the famine were the great importance of potatoes in the diet at the time and the fact that the potatoes grown then were very similar genetically. This low genetic diversity meant that the existence of a potato with genetic resistance to the pathogen was unlikely.

Important Pathogens

Today Saprolegnia and Phytophthora are significant pathogens that can produce major effects in the environment. They are interesting organisms, despite the harm that they can cause. I think that studying them is a worthy pursuit. Preventing or treating fish disease and enabling crops to survive are important goals. Exploring the nature and behaviour of oomycetes may help scientists to understand the living world better and might be beneficial for us in multiple ways.

References

Introduction to the Oomycota from the University of California Museum of Paleontology (Oomycota is another name for the oomycetes.)

Introduction to Oomycetes from the American Phytopathological Society or APS

More facts about oomycetes from the APS

Saprolegnia in fish from fuffyfish.org

Late blight in potato from North Dakota State University

Information about late blight in potatoes and tomatoes from the British Columbia Ministry of Agriculture

Information about the strain of Phytophthora infestans that caused the Irish potato famine from the phys.org news site

Questions & Answers

    © 2018 Linda Crampton

    Comments

      0 of 8192 characters used
      Post Comment

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Hi, Adrienne. I appreciate your comment. It's certainly a scary thought that the local potato crop was affected so badly. It must have been a terrible time for the people who relied on potatoes for nourishment.

      • alexadry profile image

        Adrienne Janet Farricelli 

        3 months ago from USA

        So scary that potatoes were almost on the brink of extinction and that so many people perished because of that. This article was very interesting and I learned a lot of new things I wasn't aware of before.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Thanks, Devika. I agree about the smell. It's certainly not a good thought!

      • profile image

        DDE 

        3 months ago

        Unique and well-informed. I learned something new here again. I can imagine a rotten potato odor not a good thought there.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Hi, Jackie. Yes, the ocean environment badly needs our help. The problems are depressing. I hope we can and do improve the situation.

      • Jackie Lynnley profile image

        Jackie Lynnley 

        3 months ago from The Beautiful South

        I have sworn off farmed fish for awhile now. Yet seeing all the trash in the sea doesn't make me feel too good about any of it.

        Maybe these new bucket containers that float in the water and collect all the waste will inspire an improved and larger version for helping to clean up our waters. Of course complete lack of filth added to our oceans and seas may be the only cure and with factories, oil spills, and careless people with no concerns for the environment growing so rapidly, I am not sure we have much hope for improvement.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        That's an interesting thought, Heidi! I hope you have a very pleasant evening.

      • heidithorne profile image

        Heidi Thorne 

        3 months ago from Chicago Area

        Ah, so that's the whole potato blight issue!

        When I see or hear about creatures (?) like these, they seem so otherworldly. I wonder, when we eventually do find life on other planets, if these types of organisms are what we'll find.

        Educated once again! Thanks for sharing your knowledge with us. Have a wonderful day!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        It's interesting to hear that potato blight likely affected your family, Bede. Thank you for the comment.

      • Bede le Venerable profile image

        Bede 

        3 months ago from Minnesota

        Linda, I hadn’t known the cause of the potato famine in Ireland. It’s likely the reason for my ancestors to immigrate to Canada in the 19th century. Let’s hope that scientists find something beneficial in the oomycetes. An interesting study.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Hi, Mary. Yes, because living things have so many features in common with respect to their biology, studying some of them may help us to understand others. Thanks for the visit.

      • aesta1 profile image

        Mary Norton 

        3 months ago from Ontario, Canada

        Linda, another interesting article on something I really don’t know about. You are right further study on these might bring more benefits. You have engaged me i this now as we try to eat more fish.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Hi, Peggy. I imagine that the people did eat the rotten potatoes when they could, but this wouldn’t have been possible in all cases. Blighted plants are often infected by secondary organisms that cause soft rot of the tubers. These organisms turn blighted potatoes into a dark, liquid mush that would be very hard to eat.

      • Peggy W profile image

        Peggy Woods 

        3 months ago from Houston, Texas

        This was a fascinating article as usual. I always look forward to learning something new from you. I noticed in the comments that supposedly humans are not affected by Saprolegnia if ingested by eating fish. What about the potatoes? I would imagine that during the potato famine if the tubers were infected with Phytophthora infestans starving people would have eaten them anyway.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Thanks for the visit, Manatita. Water molds are interesting organisms to investigate.

      • manatita44 profile image

        manatita44 

        3 months ago from london

        These algae and fungi research are very deep. I did not do so much at school. Fascinating to see the sexual reproduction and to know of the effects they have on fish and potatoes.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Hi, Flourish. Connections in science are often very interesting!

      • FlourishAnyway profile image

        FlourishAnyway 

        3 months ago from USA

        Who knew there was a connection between modern losses on salmon farms and the Irish Potato Famine that instigated not only massive human death and suffering but a huge migration pattern?

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        That's a good point, Larry! Thanks for the visit.

      • Larry Rankin profile image

        Larry Rankin 

        3 months ago from Oklahoma

        Sometimes it's the smallest things in the world the world that cause the biggest impact.

        Great read!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Hi, Mary. Experts say that Saprolegnia doesn't infect humans. They also say that it's best to cook fish to destroy a range of parasites. I haven't yet found any information about whether chemicals made by the mold can hurt us.

        I doubt whether we'd notice the mold after the cooking and canning process has finished. I hope a fish processor wouldn't use a fish heavily infested by Saprolegnia, though. Thanks for the comment and the interesting questions.

      • Blond Logic profile image

        Mary Wickison 

        3 months ago from Brazil

        Although when affecting potatoes and tomatoes we would see a disease and it would never make it to market or in our own gardens we would discard it.

        However, if this was processed into canned salmon, would we notice it? Would it be harmful to us?

        Another fascinating article.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Hi, Bill. Thank you so much for the visit and the comment.

      • billybuc profile image

        Bill Holland 

        3 months ago from Olympia, WA

        Another great biology lesson. I learn every single time from you, Linda!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 months ago from British Columbia, Canada

        Thank you very much for the comment, Peg. I appreciate your kindness.

      • PegCole17 profile image

        Peg Cole 

        3 months ago from Dallas, Texas

        I was always curious about the Irish potato famine and its causes. You've made the information interesting, educational and understandable. I wish you had been my biology teacher in high school and that I had paid more attention in class. Fascinating stuff.

      working

      This website uses cookies

      As a user in the EEA, your approval is needed on a few things. To provide a better website experience, owlcation.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

      For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://owlcation.com/privacy-policy#gdpr

      Show Details
      Necessary
      HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
      LoginThis is necessary to sign in to the HubPages Service.
      Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
      AkismetThis is used to detect comment spam. (Privacy Policy)
      HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
      HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
      Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
      CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
      Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
      Features
      Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
      Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
      Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
      Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
      Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
      VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
      PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
      Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
      MavenThis supports the Maven widget and search functionality. (Privacy Policy)
      Marketing
      Google AdSenseThis is an ad network. (Privacy Policy)
      Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
      Index ExchangeThis is an ad network. (Privacy Policy)
      SovrnThis is an ad network. (Privacy Policy)
      Facebook AdsThis is an ad network. (Privacy Policy)
      Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
      AppNexusThis is an ad network. (Privacy Policy)
      OpenxThis is an ad network. (Privacy Policy)
      Rubicon ProjectThis is an ad network. (Privacy Policy)
      TripleLiftThis is an ad network. (Privacy Policy)
      Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
      Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
      Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
      Statistics
      Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
      ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
      Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)