Myrtle rust under the microscope

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

Posted on February 1, 2024 05:22 AM by myrtle_rust_martino