Gum Tree Guardians's Journal

As myrtle rust March kicks off, you may have noticed some extra media attention recently with ALA kicking off the myrtle rust citizen science campaign. Thanks to the campaign, we have some new members joining our myrtle rust monitoring community. I want to welcome all the new members of Gum Tree Guardians project, and hope you find the journal posts insightful.

In the previous journal post, I introduced the initiation of the infection process when myrtle rust meets a Myrtaceae plant. We discussed the process from spore germination, to infiltration of the plant material, and how differences in the plant surfaces can influence this process. But what happens underneath the surface of the plant? How do plants defend themselves once the fungus is inside the plant? The answer lies in the plant's immune system.

When we think about immunity, we often think about our own immune system. Animals have two types of immune systems: innate and adaptive. The innate immune system can be thought of as the surveillance system, monitoring for signs and patterns of invasion. The adaptive immune system on the other hand "learns" from previous infection to respond to the same pathogen in the future.

It might be surprising to learn that it's not just animals that have a sophisticated immune system. However, unlike animals, plants lack an adaptive immune system and instead rely only on their innate immune system to fight off the great number of pests and pathogens they are exposed to throughout their lives. The plant innate immune system can be divided into two branches, PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI).

Fungal pathogens such as myrtle rust have hardy cell walls which provide support and protection to the fungus. This cell wall can also alert the plant to the presence of the pathogen. During PTI, receptors on the surface of plant cells recognise and bind molecules common to many different pathogens including the components of fungal cell wall. Recognition and binding of these molecules triggers a series of defence responses from the plant to stop infection.

Some pathogens have evolved to evade this line of defence by generating small molecules that interfere with the plant's defence mechanisms. These molecules are called effectors and they target different lines of the plants defence systems allowing the pathogen to go undetected in susceptible plants. Plants have developed mechanisms to fight back with some plants evolving to recognise the presence of these effectors. During ETI, receptors within the plant cells detect the presence of these effectors and trigger a response called the hypersensitive response. This incredible response involves the plant killing off the myrtle rust infected plant cells. As myrtle rust needs a living plant host to survive, this process takes away the nutrient source myrtle rust feeds off which stops it from completing it's life cycle.

The figure below sums up our previous couple of Journal posts is a great diagram!

---

Myrtle rust infection process from Chock, 2020 http://dx.doi.org/10.1016/j.cropro.2020.105176

---

This process helps us to understand why we may observe a plant very heavily infected with myrtle rust, while the plant next to it shows no signs of infection. When you observe a heavily infected plant in the bush or your home garden, that plant lacks the immune system to be able to fight off the infection.

Scientists are working to understand how the the plant immune system differs between resistant and susceptible Myrtaceae species to work towards determining which species may be most at risk from myrtle rust. It can provide an opportunity in the future to safeguard some of our vulnerable Myrtaceae species through breeding efforts. Work is also underway to identify the effectors which myrtle rust releases into the plant to better understand how the fungus is able to go undetected by the plant immune system.

I hope you've enjoyed reading some of the science of myrtle rust infection and immunity! As always, throw your questions or comments into the comments section below. Please let me know if there are any other myrtle rust topics you'd like a write up on! And as always, thank you for your contributions to the project.

Alyssa

Have you ever noticed that myrtle rust symptoms appear on the newly emerged parts of plants, such as the new leaves, fruits, or flowers? Behind this small detail lies a big clue about how myrtle rust spores are able to enter the host tissues.

So how does myrtle rust infect plants? What are the mechanisms that allow this fungus to penetrate the host tissues and cause disease? In this post, we will briefly explore the initiation of the infection process of myrtle rust.

Myrtle rust disease on cultivated Pilidiostigma glabrum captured by @tonyrddd

---

The infection process of myrtle rust begins with the spores. In our previous journal post I introduced these tiny reproductive structures of the fungus which are dispersed by wind, water, insects, animals, and human activities. Given the right environmental conditions, these spores “wake up” in a process called germination. This process requires dark and moist conditions along with mild temperatures (between 15°C and 25°C). These conditions are often met during the night, when dew forms on the plant surfaces, or during periods of rain or irrigation.

During germination, a thin threadlike outgrowth, termed a germ tube, forms from the spore and grows towards the plant surface. The germ tube then forms a structure called an appressorium, which is a flattened and swollen tip that adheres to the plant surface. For most rust fungi, this appressorium seeks out openings in the plant surface to enter the plant. Unlike most other rust fungi, myrtle rust goes in guns blazing, taking a more aggressive approach to entering the plant.

After the formation of the appressorium, the tip of which is termed the penetration peg, exerts an enormous amount of pressure that is able to pierce directly through the plant surface to reach the nutrient containing cells under the surface. This mechanism is usual for rusts, but has been observed and studied in soybean rust.

The fungus relies on and recognises the physical traits of the plant surface to initiate germination such as texture and chemical components. There are however many properties of the plant surface which protect the plants from invasion such as the presence of waxes, cuticles, hairs, or glands that can prevent the attachment or penetration of the fungal spores. In the case of leaves as they mature, these wax layers increase in thickness and complexity. This change reduces the ability of the fungus to recognise the plant leading to reduced germination, while also making penetration of any germinated spores challenging due to this increased thickness.

As a result of this unique penetration mechanism, myrtle rust spores are generally only observed on the new tissues of susceptible plants as they are less hardy and provide the right physical cues for spores to germinate. In the case of resistant plants which show no signs of myrtle rust infection, some scientists are working to identify if there are changes to the leaf structure and chemical composition that prevent myrtle rust infection even in young leaves.

If you see a healthy plant in a myrtle rust impacted area, please upload it to iNaturalist as this may give scientists clues as to what makes these plants resistant to the fungus.

Next time you spot myrtle rust on a hike, in your neighbourhood, or in your garden, be sure to take note of which parts of the plant are infected. You may even be able to spot the tell-tale signs of previous infection that may remain on older plant parts.

In a future post we'll dive into what is happening once fungus has infiltrated under the leaf surface. Until then, if you have any burning questions about myrtle rust, throw them in the comments below and we can answer them in the next journal post!

Thank you all for your contributions.

Alyssa

Welcome to 2024 Gum Tree Guardians. A big thank you for all your contributions in 2023. With your help, we managed to triple the number of myrtle rust observations here on iNaturalist in just 12 months, providing key insights into the spread of the pathogen in Australia.

With all these new observations, have you ever wondered why myrtle rust is able to spread so easily? Microscope images uploaded by Gum Tree Guardian member @montana_h tells us a lot about what makes rust fungi like myrtle rust spread so easily.

One of the reasons why myrtle rust spreads so easily is because of its urediniospores. These spores are tiny reproductive structures that can be carried by wind, insects, animals, or humans. The spores are produced in the plant and eventually burst out from the leaf surface to create pustules, which are the yellow powdery bumps we see on the surface of infected leaves.

A single pustule contains thousands of spores, and all it takes is for a single spore to land on a susceptible host in the right conditions for infection to begin. The images uploaded by @montana_h of myrtle rust spores under the microscope show how numerous they are. These spores can survive months at a time before landing on a new susceptible host and causing infection.

Myrtle rust spores at 400x maginification by @montana_h

---

In situations where trees are heavily infected, or there are many trees infected, the spore load (the total number of spores) increases. With this increase, comes an increase in the spread of the spores which results in more trees infected. More infection = more spores = more infection and so on.

So, what can we do to reduce the spore load?

• Monitor its occurrence and report any sightings to the relevant authorities, and here on iNaturalist.
• Look but don’t touch. While observations are needed, it’s important to not touch the infected plants where possible.
• Follow biosecurity measures to avoid introducing or spreading the disease to new areas or vulnerable species. This includes washing all clothes after being in nature, and going in with clean clothes. Washing footwear is also essential to stop the spread of soil borne pathogens.
• In your home garden, remove infected leaves by using a combination of fungicides and solarisation. If a plant is infected once, it means it is susceptible to myrtle rust and will get infected again. If you can part with it, consider replacing the plant with a myrtle rust tolerant plant instead

If you have any burning questions about myrtle rust, throw them in the comments below and we can answer them in the next journal post! Thank you all again for your contributions.

Alyssa

After a short break, we're back with the latest updates for Gum Tree Guardians.

As always we start with a big welcome to the new members of the project. We welcome @ayenson, @katie11022, @kevin-jackson, @eroger, @isaiahfindley, @richie_south, @lauramontuna, @claudslee, and @jjungfels to the project. We look forwards to seeing your observations and thank you to the current members who have continued to add myrtle rust observations.

From July to September, 26 new observations were added to the Gum Tree Guardians project. Observations spanned from Smithfield in Queensland, down to Wollongong in New South Wales. Infections were observed on Melaleuca quinquenervia, Eugenia reinwardtiana, Rhodamnia rubescens, Gossia punctata, Syzygium jambos, Rhodamnia dumicola, Syzygium australe , Rhodamnia maideniana, and Lenwebbia prominens.

---

Our September observation of the month comes from Smithfield Regional Park in Queensland with a heavy infection on Eugenia reinwardtiana. Thank you @ryanthughes for adding this great image!

Myrtle rust spores on juvenile leaves and petioles of Eugenia reinwardtiana by @ryanthughes

---

Remember, if you come across a myrtle rust infected plant, don't touch it. The spores can spread easily, so it's best to keep your hands off. Take a picture of the infected material and some photos of the entire plant to help us identify the host plant. Then upload the photos to iNaturalist, including the location, which will automatically add the images to the Gum Tree Guardians project.

Being a Gum Tree Guardian is about more than just monitoring and reporting on myrtle rust infected plants. It's also about raising awareness of the importance of Myrtaceae plants in our unique ecosystem. If your friends or family aren't already part of the Gum Tree Guardians project on iNaturalist, why not encourage them to join us and start making a difference today?

Together, we can protect our native Myrtaceae plants and preserve our beautiful ecosystem for generations to come. Thank you again for your contributions,
Alyssa

Another month has passed which brings us to the June updates for Gum Tree Guardians. As always we start with a big welcome to the 14 new members of the project and thank you to the current members who have continued to add myrtle rust observations.

With winter in full swing, we expect to see less myrtle rust infection across the country. This was reflected in the downtick in June observations, with 18 new observations added to the project over the month. Observations spanned from Yeppoon in Queensland, down to Melbourne with infection observed on Melaleuca quinquenervia, Xanthostemon chrysanthus, Rhodamnia rubescens, Rhodamnia acuminata, Gossia acmenoides, Asteromyrtus symphyocarpa, Callistemon sp Hinchinbrook, Metrosideros excelsa, Syzygium jambos, and Melaleuca trictostachyea.

Remember, if you come across a myrtle rust infected plant, don't touch it. The spores can spread easily, so it's best to keep your hands off. Take a picture of the infected material and some photos of the entire plant to help us identify the host plant. Then upload the photos to iNaturalist, including the location, which will automatically add the images to the Gum Tree Guardians project.

---

While June was a quiet month for myrtle rust infections, it was a busy time for expects working in the myrtle rust space. The Australasian Myrtle Rust Conference was held at The University of Sydney from June 21 – 23rd and brought together experts from Australia, New Zealand and beyond to discuss the current state of research and management of the pathogen at a domestic and international level.

If you haven’t already, check out the highlights of the event below!

You can view all of the talks from the 3-day event on the Australian Network for Plant Conservation’s YouTube page: https://www.youtube.com/@AnpcAsnAu. The Network’s website has also put together some great resources and information on myrtle rust. Be sure to head over to their website if you haven’t already: https://www.anpc.asn.au/myrtle-rust/

---

Being a Gum Tree Guardian is about more than just monitoring and reporting on myrtle rust infected plants. It's also about raising awareness of the importance of Myrtaceae plants in our unique ecosystem. If your friends or family aren't already part of the Gum Tree Guardians project on iNaturalist, why not encourage them to join us and start making a difference today?

Together, we can protect our native Myrtaceae plants and preserve our beautiful ecosystem for generations to come. Thank you again for your contributions,
Alyssa

May is over and what a month it was for Gum Tree Guardians! A big welcome to the 38 new members of the project. It’s wonderful to have you all on board and I’ve loved watching our community grow. Let’s dive into the updates for May!

An additional 26 observations were added over the month of May on a wide range of Myrtaceae species including Melaleuca quinquenervia, Backhousia citriodora, Gossia gonoclada, Gossia acmenoides, and the majority of observations on Rhodamnia rubescens, . The observations spanned as far North as Cairns all the way down to Mollymook.

---

I wanted to highlight this observation from Gum Tree Guardian @porcoespinho15 who joined the project in May and coincidently discovered a myrtle rust infection in his garden. This observation is a great example of the development of myrtle rust symptoms that appear throughout the pathogens life cycle.

Myrtle rust on leaves of Backhousia citriodora by @porcoespinho15. Image 1 and 2 display symptoms on juvenile leaves. Image 1 shows pustules developing on the juvenile leaves and Image 2 shows the pustules once they have fully developed. Image 3 shows older pustules. These would have infected the leaf when it was young and no new infection begins as the leaf matures.

---

Remember, if you come across a myrtle rust infected plant, don't touch it! The spores can spread easily, so it's best to keep your hands off. Take a picture of the infected material, and some photos of the entire plant if possible, to help us identify the host plant. Then, upload the photos to iNaturalist, including the location, which will automatically add the image to the Gum Tree Guardians project.

Being a Gum Tree Guardian is about more than just monitoring and reporting on myrtle rust infected plants. It's also about raising awareness of the importance of Myrtaceae plants in our unique ecosystem. If your friends or family aren't already part of the Gum Tree Guardians project on iNaturalist, why not encourage them to join us and start making a difference today? https://inaturalist.ala.org.au/projects/gum-tree-guardians

Together, we can protect our native Myrtaceae plants and preserve our beautiful ecosystem for generations to come.

Thank you again for your contribution to science,

Alyssa

Happy Monday Guardians and welcome to our new members!

I’m here with a quick update of your observations from April. Firstly, a big thank you to those who have joined the project and shared to details with others in their community. By sharing the project, you’re helping to raise awareness of the impacts of myrtle rust on Myrtaceae plants and how we can best protect them.

Before diving into April’s numbers, we had a concerning observation backdated from March. Member Damien spotted rust infecting juvenile leaves of Eucalyptus eugenioides in New South Wales. While it’s uncommon to see infection on Eucalyptus, the juvenile leaves are often susceptible especially when conditions are favourable. Please be extra vigilant and if you see yellow spores on Eucalyptus and please log it through the app!

Myrtle rust spores on juvenile leaves of Eucalyptus eugenioides by @damien_vella12

---

Onto our April stats! An extra 12 observations were added over the month on a range of Myrtaceae species including on Rhodamnia maideniana, Melaleuca quinquenervia, Backhousia leptopetala, Eugenia reinwardtiana, and Austromyrtus tenuifolia. The observations spanned as far North as Cape Tribulation all the way down to Sydney.

Remember, if you come across a myrtle rust infected plant, don't touch it! The spores can spread easily, so it's best to keep your hands off. Take a picture of the infected material, and some photos of the entire plant if possible, to help us identify the host plant. Then, upload the photos to iNaturalist, including the location, which will automatically add the image to the Gum Tree Guardians project.

Being a Gum Tree Guardian is about more than just monitoring and reporting on myrtle rust infected plants. It's also about raising awareness of the importance of Myrtaceae plants in our unique ecosystem. If your friends or family aren't already part of the Gum Tree Guardians project on iNaturalist, why not encourage them to join us and start making a difference today? https://inaturalist.ala.org.au/projects/gum-tree-guardians

Together, we can protect our native Myrtaceae plants and preserve our beautiful ecosystem for generations to come.

Thank you again for your contribution to science,

Alyssa

Hello Gum Tree Guardians!

I'm thrilled to welcome any new members to our amazing community. Thanks to your hard work and dedication, we've been able to keep a watchful eye on the health of our Myrtaceae plants, especially with the recent detection of myrtle rust on Lord Howe Island.

Since I launched the Gum Tree Guardians project in January, we've had a whopping 42 members join us! Together, you've logged 32 observations of myrtle rust infected plants from the Sunshine Coast all the way to Northern Tasmania. Thank you so much for your efforts - we couldn't do this without you.

It's important to note that myrtle rust symptoms can take many forms, not just the tell-tale yellow spores. It could look like pimple-like bumps, twisted leaves, or even dark patches on the leaves or stems. By sharing your photos and data of infected Myrtaceae plants on iNaturalist, we can better understand the impact of myrtle rust and develop strategies to protect our precious native plants.

Remember, if you come across a myrtle rust infected plant, don't touch it! The spores can spread easily, so it's best to keep your hands off. Take a picture of the infected material, and some photos of the entire plant if possible, to help us identify the host plant. Then, upload the photos to iNaturalist, including the location, which will automatically add the image to the Gum Tree Guardians project.

Being a Gum Tree Guardian is about more than just monitoring and reporting on myrtle rust infected plants. It's also about raising awareness of the importance of Myrtaceae plants in our unique ecosystem. These plants provide essential food and shelter for our native animals, so it's critical we keep them healthy and thriving.

I can't thank you enough for your contribution so far, and I encourage you to keep up the fantastic work. If your friends or family aren't already part of the Gum Tree Guardians project on iNaturalist, why not encourage them to join us and start making a difference today? Together, we can protect our native Myrtaceae plants and preserve our beautiful ecosystem for generations to come.

Thank you again for your contribution to science,
Alyssa

What is myrtle rust? Where did it come from? How do I treat it? How do I prevent it? What do I do if I see it? These are just a few of the questions you have been asking and I’m here to answer them for you!

Q: What is myrtle rust?
A: Myrtle rust is a fungal disease that affects plants in the Myrtaceae family, including native species such as eucalypts, paperbarks, guava, lilly pillies, and tea trees. The disease is caused by the fungus Austropuccinia psidii.

Q: Where did myrtle rust come from?
A: Myrtle rust is believed to have originated in South America, where it was found to be infecting trees in Eucalyptus plantations. It has since spread to many other parts of the world, including Australia as of 2010, New Zealand, and parts of Asia.

Q: How does myrtle rust spread?
A: Myrtle rust is spread by wind, rain, and human activities such as the movement of infected plants or plant material. The spores of the fungus can be carried long distances by the wind, and can also be spread by rain splashing on infected plants and dispersing the spores.

Q: What are the symptoms of myrtle rust?
A: The most common symptoms of myrtle rust include the appearance of bright yellow powdery spots on the emerging leaves, stems, and fruit of infected plants. The spots may merge to form large lesions, and the infected plant may experience stunted growth or dieback. Some symptoms are more cryptic, especially in the early stages of infection. Keep an eye out for distortion of the edges of the leaves and red/purple raised bumps on the leaf surface.

Q. What should you do if you see myrtle rust?
A. If you suspect a myrtle rust infection, you can follow the below steps:

1. Don’t touch the infected material or attempt to take a sample.
2. Take a photo of the infection and a few photos of the plant it is infecting.
3. Upload the images to the iNaturalist app. If you are in WA or SA it is important you report suspected sightings to the local government as the pathogen has not established in these states. A list or contact details is provided at the bottom of this FAQ.

Q: Can myrtle rust be treated?
A: There is currently no cure for myrtle rust but researchers are working on ways to identify plants that are susceptible or resistant to the disease. If you have an infected plant in your garden, you may decide to destroy the plant to prevent the disease from spreading. Fungicides may be used to protect healthy plants from becoming infected, however their efficacy against myrtle rust is limited.

Q: How can I prevent myrtle rust from infecting my plants?
A: The best form or prevention is to avoid planting susceptible species in your garden, especially if you are in an area where disease is known to occur. If you purchase a new plant from a nursery, be sure to inspect it carefully for any signs of infection before bringing it home.

Q: Are all Myrtaceae plants susceptible to myrtle rust?
A: Not all Myrtaceae plants are equally susceptible to myrtle rust. Some species are more resistant to the disease than others, but we are still in the early stages of understanding the potential impact of the disease. Unfortunately, many native species in Australia are highly susceptible, and the disease poses a significant threat to their survival. Monitoring the spread of the disease will provide a clearer picture of the spread of the pathogen, and the species it impacts.

Q: What is being done to control the spread of myrtle rust?
A: Governments, researchers, and industry groups in affected countries are working together to monitor the spread of myrtle rust and develop strategies for managing and controlling the disease. This includes measures such as surveillance, quarantine, and education campaigns to raise awareness of the disease and how to prevent its spread. As a Gum Tree Guardian, your observations are highly valuable to these efforts.

Contacts if you spot myrtle rust in WA or SA
Western Australia: DPIRD Pest and Disease Information Service 9368 3080 or padis@dpird.wa.gov.au
South Australia: Emergency Plant Pest Hotline on 1800 084 881 or PIRSA.planthealth@sa.gov.au

If you have any more questions, pop them in them in the comments below.

All the best,
Alyssa

What is Gum Tree Guardians?

Gum Tree Guardians is a project on the iNaturalist platform to monitor the spread of myrtle rust in Australia. This project has been generously funded by Eucalypt Australia through a Dahl Fellowship and can be viewed here: https://inaturalist.ala.org.au/projects/gum-tree-guardians

What is myrtle rust?

Myrtle rust is a disease caused by the fungal pathogen Austropuccinia psidii, affecting trees within the family Myrtaceae. This family includes over 330 genera, including our iconic Eucalyptus and Melaleuca just to name a couple! The disease is typified by the appearance of yellow spores on susceptible plants with symptoms appearing on young plant tissue such as leaves, stems, flowers, and fruit. Multiple infections can lead to severe defoliation and plant death. The spores produced by the pathogen, are easily spread to other plants through the wind or by human movement on clothes or transportation of infected material. Examples of symptoms on a range of plants can be viewed here: https://agriculture.vic.gov.au/biosecurity/plant-diseases/shrub-and-tree-diseases/myrtle-rust/myrtle-rust-host-plants-and-symptoms

Where did it come from?

The threat to Australian Eucalyptus and Myrtaceae was realised when A. psidii began causing major damage in Eucalyptus plantations in Brazil. Although strict biosecurity measures were put in place to keep A. psidii out of Australia, the pathogen was discovered in Australia in 2010. First detected in New South Wales, it has since been spread to Queensland, Victoria, the Australian Capital Territory, Tasmania, the Northern Territory, and Western Australia.

Why do we need your help?

A particular challenge for myrtle rust research is monitoring the spread of the pathogen and detecting new incursions. Myrtaceae are one of the top species rich families in Australia, widely distributed throughout Australia. To predict where an incursion may occur, climatic modelling has been developed to determine the climatic suitability of A. psidii across Australia. These models can be overlapped with Myrtaceae species distribution maps to narrow down areas of high risk of an incursion. Of particular concern is climatic suitability within the Eucalyptus rich biodiversity hotspot of South-West Western Australia. With Myrtaceae in this region already under threat by soil-borne pathogens such as Phytophthora cinnamomi, monitoring of plants within such regions is imperative to ensure the pathogen is acted upon swiftly in the event of an incursion to ensure the survival of the species.

How will the data be used?

The data obtained from the project will provide valuable data for both researchers and conservationists alike. This data can serve myrtle rust research in many ways. Firstly, it can used to identify new species of Myrtaceae susceptible to the pathogen that have not already been identified. Further, if myrtle rust is detected in a new location (on any species), it will allow for Myrtaceae species in those areas to be tested for their response to the pathogen and seed collected for conservation. The identification of myrtle rust in a new locations will also inform researchers of the spread of the pathogen, also aiding conservation efforts.

How do you add an observation?

Contributing to the Gum Tree Guardians project is easy! Once you have created an account on iNaturalist Australia (https://inaturalist.ala.org.au/signup), you’re ready to start uploading your observations. Please remember, myrtle rust spores spread very easily. If you observe myrtle rust on any Myrtaceae species, it is important that you DO NOT TOUCH IT to avoid spreading it to other trees or areas.

1. Take several close up image of symptoms. This is usually yellow spores which can appear on leaves, stems, flowers, or fruit
2. Take an image on the whole plant if possible to assist with identification and to show the surrounding environment
3. Upload observation to the iNaturalist platform using your phone or web browser. If possible, include the plant it was identified on in the comments section.

Myrtle rust observations will automatically be added to the Gum Tree Guardians project. You can view the project and become a member here: https://inaturalist.ala.org.au/projects/gum-tree-guardians and a guide is available to make uploading as easy as possible: https://inaturalist.ala.org.au/pages/getting+started

Happy observing,

Alyssa (project administrator)