Development of DNA-based, diagnostic tools to detect and identify invasive forest pathogens in the field and ports of entry

Climate change will dramatically alter vulnerable areas impacted by invasive and emerging forest pathogens within the Pacific Islands and associated underrepresented communities. Forest managers and forest health professionals all face challenges when identifying forest pathogens that cause diseases and assessing the resulting impacts of forest disease under changing climates.

Myrtle rust (Austropuccinia psidii) on rose apple (Syzygium jambos). Photo by Mee-Sook Kim, USDA Forest Service.

Previously, pathogen identification relied primarily on symptoms, but many symptom-based identifications are inaccurate and unreliable. Today, powerful, fast, and economical DNA-based technologies are available for identifying many forest pathogens and their hosts. For example, DNA-based field diagnostic tools can be applied locally to detect and identify invasive forest pathogens at points of entry.

This project focuses on two invasive forest pathogens: Austropuccinia psidii, which causes myrtle rust disease, and Phellinus noxius, which causes brown root rot disease. These two pathogens result in destructive growth loss and mortality of trees in diverse forest ecosystems.

Myrtle rust disease causes severe damage to myrtaceous plants in the Tropics and Neotropics. Susceptible myrtaceous plants include many species of cultural, economic, and ecological importance (e.g., ōhi’a, lemon myrtle, guava, rose apple, eucalypts, allspice, and many rainforest, understory species). The myrtle rust pathogen can spread rapidly, with the potential to cause widespread damage to natural ecosystems.

In recent years, myrtle rust has spread within South and Central America, Caribbean, Hawaii, Oceania, Southeast Asia, and South Africa. Our preliminary bioclimatic models suggest that myrtle rust will continue its spread to susceptible hosts within diverse regions with suitable climate, such as many of the U.S.-affiliated Pacific Islands. Despite the potential threats to numerous forest ecosystems world-wide, the expanding geographic range of myrtle rust, and the threat that new biotypes may be introduced to some regions, we lack effective means to rapidly detect and intercept myrtle rust pathogens. Currently available methods for identifying pathogen biotypes are costly and time consuming because they require specialized laboratory equipment and highly technical expertise for DNA-based genotyping.

Phellinus noxius causes brown root rot disease in hundreds of diverse tropical tree species (e.g., breadfruit and mango) that are integral to forest ecosystems, economies, and native cultures in the Pacific Islands. The human-associated spread of brown root rot disease into uninfected areas is a major concern. In addition, climate change is predicted to exacerbate negative impacts of brown root rot disease in these regions. Phellinus noxius represents a major invasive threat to U.S. states and territories (e.g., Hawaii, Florida, Puerto Rico). Our recent work indicates that it is more prevalent and aggressive than previously reported in the Pacific Islands.

Although local and regional partners from these communities are eager to detect and prevent the spread of invasive forest pathogens, their engagement in these activities is limited by lack of expertise, diagnostic tools, and infrastructure. For these reasons, we propose further developing established national and international collaborative efforts in the U.S.-affiliated Pacific Islands and other global regions at risk for pathogen invasion under changing climates.

Partners, including forest pathologists, forest managers, forest health specialists, and other forest and horticultural professionals from U.S. states and U.S.-affiliated Pacific Islands will be instrumental in testing, adapting, and using the diagnostic tools developed by this project.

Objectives

1. This project will produce DNA-based, diagnostic tools that provide rapid (~1 hour) detection of priority invasive fungal pathogens, exemplified by the invasive myrtle rust pathogen (Austropuccinia psidii) and brown root rot pathogen (Phellinus noxius; black-sock fungus).
2. We will conduct bioclimatic models for assessing present and future risks posed by A. psidii and P. noxius to help identify priority areas for preventing the introduction of these invasive pathogens.
3. We will provide stakeholder groups with the diagnostic technology and training to aid in rapid detection, management, and containment of invasive forest pathogens.

Products

• Bioclimatic maps indicating where myrtle rust and brown root rot pathogens are likely to subsist under contemporary and future climates.
• A publication detailing the development of field-ready diagnostic kits (e.g., LAMP assay sets) for myrtle rust and brown root rot pathogens.
• A publication detailing the potential distribution of these pathogens under changing climates.

Expected Outcomes

• This project will improve detection and prevention strategies for new myrtle rust pathogen (A. psidii) biotypes and the brown root rot pathogen (P. noxius) in the Pacific Islands, Hawaii, Australia, New Zealand, and other regions. This project will also support rapid and economical detection of myrtle rust and brown root rot within regions where is not known to occur (e.g., U.S.-affiliated Pacific Islands, California, and other global regions).
• The resulting information and tools will help to prevent the introduction of new pathogen biotypes into areas where one biotype is already established. A parallel project using the same approaches will also contribute to diagnostic tools for the detection of the brown root rot pathogen (P. noxius) in areas where it does not exist, but poses a threat, such as Hawaii, Puerto Rico, Florida, California, and other global regions.

Metrics of Success

Partners will deploy the DNA-based, field-ready tools in multiple locations including ports of entry. Our technology will help minimize spread of myrtle rust pathogens to uninfected forests, nurseries, and orchards, including those in the U.S.-affiliated Pacific Islands. Overall, our project will maintain the resiliency of myrtaceous plants so they can continue to provide broad cultural, economic, and ecological benefits.

Geographies: Pacific Islands, Hawaii, Australia, New Zealand, and other regions