Myrtle rust facts for kids

Quick facts for kids Myrtle rust
On Eugenia reinwardtiana
Scientific classification
Kingdom:	Fungi
Division:	Basidiomycota
Class:	Pucciniomycetes
Order:	Pucciniales
Suborder:	Uredinineae
Family:	Sphaerophragmiaceae
Genus:	Austropuccinia
Species:	A. psidii
Binomial name
Austropuccinia psidii (G. Winter) Beenken (2017)
Synonyms
Puccinia psidii G. Winter (1884) Uredo rangelii J.A. Simpson, K. Thomas & Grgur. (2006) [1]

Austropuccinia psidii, commonly known as myrtle rust, guava rust, or ʻōhiʻa rust, is a type of fungus. It is a plant pathogen that naturally comes from South America. This fungus mainly attacks plants in the Myrtaceae family.

Myrtle rust is part of a group of fungi called the guava rust group. Its spores are bright yellow to orange. Sometimes, they have a purple ring around them. You can find these spores on new plant parts like shoots, leaves, buds, and fruits. Infected leaves often twist and may die. If a plant is very sensitive to the rust, the infection can even kill the whole plant.

By late 2013, myrtle rust had infected about 179 plant species in New South Wales and Queensland, Australia. These species came from 41 different plant groups. This means it affected almost half of all plant groups in the Myrtaceae family in Australia.

Why Myrtle Rust is Important

Myrtle rust, or Austropuccinia psidii, can infect many different types of plants. This makes it hard to control and stop its spread. However, it has also been found to have some helpful uses.

For example, in Florida, this fungus has been looked at as a way to control an invasive Australian plant. This plant is called Melaleuca quinquenervia. It is a weed tree that has taken over parts of south Florida. If not stopped, it could seriously harm the natural ecosystems there. It could turn marshes in the Everglades into swamps.

Myrtle rust can spread quickly around the world. It can harm important plants in the Myrtaceae family. These include plants like Archirhodomyrtus beckleri, Decaspermum humile, Gossia hillii, and Rhodamnia maideniana. These plants are very important for Australia's native forests. The rust can even cause some plant species to disappear forever.

This fungus is a big problem because it spreads easily. It produces many tiny spores that the wind can carry over long distances. Animals like birds, bats, possums, and insects can also spread the spores if they touch infected plants. Myrtle rust can cause a lot of damage to natural ecosystems. In Australia, many forests are full of Eucalyptus trees. Eucalyptus is also the main tree in most of Hawaii's forests. When myrtle rust infects these trees, it can change how forests look and work. This can harm the many different plants and animals living in these ecosystems.

How Myrtle Rust Got Its Name

Scientists first officially described this fungus in 1884. They called it Puccinia psidii. Later, in 2006, other scientists described it again and named it Uredo rangelii. Finally, in 2017, a scientist named Beenken put these names together. He placed the fungus in a new group, giving it the name Austropuccinia psidii.

Signs of Infection and How it Develops

Myrtle rust usually shows up as tiny yellow spots on the underside of leaves. However, you might also see these spots on the top of leaves or on young stems. At first, the disease looks like small purple or reddish-brown spots. These spots might have a faint yellow ring around them. As the rust grows, these spots join together to form bright yellow bumps called pustules.

Over time, these yellow pustules often turn a grey-brown color. If many pustules join together, the leaf can become twisted. Myrtle rust also makes plants more likely to get other infections. These new infections can appear just days after the first rust spots.

Myrtle rust grows best when certain conditions are met. It likes new plant tissue, high humidity, and water on the plant surface for more than six hours. Moderate temperatures, around 15–25 °C (59–77 °F), are also good for it. If there is low light for at least eight hours after spores land on a plant, they are more likely to grow.

Myrtle rust can spread in many ways. It can move through infected plant material or contaminated tools. Wind, water, and even gravity can carry the spores. Animals, humans, and vehicles can also spread the rust if they come into contact with it.

The fungus can complete its entire life cycle on a single plant. This process can happen very quickly, sometimes in as little as 10 to 14 days.

Myrtle Rust as an Invasive Species

Myrtle rust can cause serious problems for many plant species in the Myrtaceae family. This family includes plants like guava, eucalyptus, and melaleuca. It also includes several plants native to Hawaii, some of which are found nowhere else on Earth. One important native Hawaiian forest tree, ʻōhiʻa (Metrosideros polymorpha), is especially at risk.

There are different types, or strains, of the Puccinia psidii rust. Some are known to be in Florida, and at least one has been reported in California. People are worried that new strains might appear that could be very damaging to ʻōhiʻa trees. These trees are a key part of many Hawaiian native ecosystems. Currently, the biggest threat in Hawaii is the damage it is doing to Eugenia koolauensis, a plant species that is officially endangered.

Myrtle rust was first found in Australia in mid-2010. It is now a major threat to Australia's ecosystems. This is because almost 80 percent of Australia's native trees are Myrtaceae. Most native animals rely on healthy trees for their survival. The rust also poses a big threat to Australia's farming and forestry industries. It has spread along much of the eastern coast of Australia.

The first time it was found was in April 2010 in Gosford in New South Wales. At first, officials tried to contain it and thought they could get rid of it. The New South Wales government spent $5 million trying to stop the disease. However, these efforts failed, and it spread quickly. A group was formed to manage myrtle rust in July 2010. But because it had spread so much, the group realized it was impossible to get rid of it completely.

Myrtle rust on ramarama (Lophomyrtus bullata), a New Zealand tree.

By December 2010, it had spread far north along the coast. It was found in South East Queensland and even in cities like Cairns and Townsville in Far North Queensland. In January 2012, a myrtle rust outbreak was reported in Victoria. It started in Melbourne's southern and eastern suburbs. Early attempts to stop it failed, and by April 2012, it had spread across much of the state.

By late 2015, myrtle rust was common in Queensland, NSW, and Victoria. It reached Tasmania in February 2015 and the Northern Territory in May 2015. The Tasmanian government is still trying to contain it. However, the Northern Territory government has decided it cannot be stopped there.

In April 2017, New Zealand's Ministry for Primary Industries reported myrtle rust on Raoul Island. The next month, it was found on the New Zealand mainland in Kerikeri. As of 2020, it is spreading in New Zealand. It is infecting trees like pōhutukawa (Metrosideros excelsa), northern rātā (Metrosideros robusta), southern rātā (Metrosideros umbellata), ramarama (Lophomyrtus bullata), and rōhutu (Lophomyrtus obcordata).

Plants Myrtle Rust Can Infect

Myrtle rust has been found on plants from the following groups:

Impacts on the Environment

Myrtle rust on lilly pilly leaves.

Since it was first found in 2010, myrtle rust has spread very fast. Now, entire plant species are in danger. In Australia, the Myrtaceae family is very diverse and widespread. This family includes eucalypts, melaleuca, and lilly pilly trees. These plants are important for many native ecosystems.

Myrtle rust has affected many forest ecosystems. These include coastal heath, wetlands, sand island ecosystems, and rainforests. About 40 plant species are now at risk of disappearing. For example, the endangered Rhodamnia angustifolia is highly sensitive to the rust.

Native animals are also likely to be greatly affected. Myrtle rust grows on shoots, fruits, and flowers. These are food sources for some animals, like flying foxes, lorikeets, and honey eaters. There is a strong chance that some of these animal species could disappear from certain areas. Their loss could then cause other serious problems in the ecosystem.

Life Cycle and Reproduction

Rust fungi often have complex life cycles. They can reproduce both sexually and asexually. Sometimes, these stages happen on different host plants. The life cycle of Austropuccinia psidii is still being studied. Some research suggests it completes its life cycle on one host. Other studies think it needs two different hosts, but the second host has not yet been found.

In simple terms, the fungus spreads its spores. These spores land on young leaves, shoots, fruits, or flower buds. Once on a plant, the spores grow and enter the plant. Inside the plant, the fungus creates special feeding structures. These structures help the fungus get nutrients from the plant.

After getting nutrients, the fungus produces more spores. These new spores can then spread to other young plant parts. This allows the disease to spread quickly and cause many infections. The fungus can also produce different types of spores that help it survive and spread further.

How Myrtle Rust is Managed

The first plan to get rid of myrtle rust from Australia was stopped in December 2010. It was decided that it was impossible to completely remove it. Instead, the focus shifted to slowing its spread and reducing its harm. The Australian Government provided $1.5 million for research into managing myrtle rust.

In 2016, a national workshop was held to discuss myrtle rust. Experts talked about research findings and future ways to manage the rust. A key agreement from this workshop was the need for a national plan. This plan aims to make sure that no plant species or ecosystems are lost because of myrtle rust.

There are practical steps people can take to help stop the spread of myrtle rust. These include:

• Not moving plant material from one place to another.
• Making sure equipment is clean before arriving at and leaving a site.
• Avoiding areas where myrtle rust might be present on plants.