A Three Pronged Approach to understanding the defensive mechanisms in Green Ash (Fraxinus, pennsylvanica) resistant to EAB (Agrilus planipennis)

March 7, 2022March 8, 2022 Monika Otting 3095 Views

2018, Jeanne Romero-Severson, PhD, University of Notre Dame

Emerald ash borer (EAB, Agrilus planipennis), an accidentally introduced Asian beetle, poses an acute threat to the native Fraxinus species in North America. Mass mortality in green ash (F. pennsylvanica) and white ash (F. americana) affects broad swaths of the landscape, from forests and farmland to urban streets. Urban foresters and communities are fighting this spread which cost upwards of 1.7 billion dollars in 2011 alone. While some communities like Naperville (a suburb of Chicago) maintain their trees by spending almost 900,000 dollars a year on chemical treatments, American ashes are being functionally removed from every other landscape.

This annihilation is due to the lack of base resistance against the invasive EAB, as American ashes never acquired necessary protections through co-evolution. However, a few green ash (<1%) termed “lingering” have been noted to survive for years after all other local green ash have died. Our collaborators collected these trees, and after challenging them with directly applied EAB, have confirmed defensive responses (killing some EAB larvae or slowing their growth) in clonally replicated studies. Because these trees appear to use different methods of resistance, these multiple traits can be ‘stacked’ or pyramided in a selective breeding program to produce trees with greater long-term resistance to EAB. We propose a multi-faceted, interdisciplinary approach to examine the functional basis for resistance to EAB in lingering green ash. We will employ transcriptomics, proteomics and metabolomics to examine differences in gene expression, proteins and secondary metabolites in susceptible green ash vs lingering green ash. We will apply this analysis to 200 progeny from lingering x lingering and susceptible x susceptible crosses in twelve different families. We propose to analyze these samples to find indicators and mechanisms of resistance. From this, we can create a test that allows us a strong prediction of resistance from a small tissue sample. This allows for a higher throughput in collecting new potential lingering trees from the wild to increase the genetic diversity in the breeding pool. By increasing the rate at which defensive traits in ash can be selected for in a targeted breeding program, we can produce an ash with enough resistance that EAB becomes a pest instead of a deadly plague. , once we can understand the defensive mechanisms, we can better guide the breeding program, vastly increasing the pace to restore green ash on the landscape and in our cities.

Study results:

Imagine a tree that protects streambanks, shelters farms from wind and blowing snow, grows rapidly, thrives in urban settings, lives for over 100 years, tolerates cold, heat and salt, has few diseases or insect pests, and displays a beautifully shaped canopy with handsome foliage. These are the ash trees native to America and they are disappearing because of emerald ash borer (EAB), an insect accidently imported from Asia. EAB is spreading rapidly across the United States, killing 98-100% of the ash trees it infests. Dead tree removal and insecticide treatments cost rural and urban communities over 1.7 billion dollars in 2011 alone and the cost continues to increase.

The good news is that a few green and white ash trees (<1%) survive for years after all other local ash trees have died. Scientists working for United States Forest Service and the University of Notre Dame have confirmed that most of these survivors have the ability to fight EAB attack and different trees use different defensive strategies. The grant provided by the Tree Fund has enabled this team of scientists to identify groups of chemical compounds that fight off EAB in individual trees and the genes that produce these compounds. This work allows us to take an important step in identifying the best offspring that will be able to kill the beetle, and survive in our forests and towns.

Although we now have offspring from crosses made with the best lingering ash parents our collaborators have, we need to verify that our set of metabolites does accurately predict which of these offspring are even better than their parents in fighting off the EAB. In developing EAB resistant ash, it is important to remember that that we want the trees to reproduce on their own. This process takes longer than selecting trees for cultivars from healthy populations because we have to produce the healthy populations first! We do not want to disappoint the foresters, the nursery owners or the homeowners with trees that are not what we said they would be. If all goes well, we anticipate that we will have some populations good enough for restoration within five years, and enough seed to release such populations a few years after that. Once these trees begin to grow and thrive, then the development of new cultivars for city streets and parts becomes a reality.

We are working on other initiatives to ensure that enough seed orchards are established to enable release of seed for restoration and cultivar development. Although we have not worked out exactly how the initial seed release will happen, who will get this seed and under what terms, we are confident that this seed release will happen. The impact will be the return of American ash trees to the landscapes where they once grew, shading our rivers, beautifying our neighborhoods and lifting our hearts with the sight of their beautiful green foliage.

Year: 2018

Funding Duration: 1.25 years

Grant Program: John Z. Duling Grant

Grant Title: A Three Pronged Approach to understanding the defensive mechanisms in Green Ash (Fraxinus, pennsylvanica) resistant to EAB (Agrilus planipennis)

Researcher: Dr. Jeanne Romero-Severson

Key words: EAB, Emerald Ash Borer

Peer Reviewed Publications from Grant:

General Audience/Trade Publications:

Professional Presentations:

Dr. Jeanne Romero-Severson

2020 – Ready, fire, aim: millions for technology, no impact on forest health. – 30th USDA Interagency Research Forum on Invasive Species – Keynote

Robert Stanley (graduate student)

2020 – Determining the defensive mechanisms in Green Ash (Fraxinus pennsylvanica) resistant to Emerald Ash Borer (Agrilus planipennis) – Plant and Animal Genome, Jan 2020 – Poster

2019 – Determining the defensive mechanisms in Green Ash (Fraxinus pennsylvanica) resistant to Emerald Ash Borer (Agrilus planipennis) – Notre Dame College of Science Joint Annual Meeting, Dec 2019 – Oral

2019 – Determining the defensive mechanisms in Green Ash (Fraxinus pennsylvanica) resistant to Emerald Ash Borer (Agrilus planipennis) – Metabolomics Society of North America, Nov 2019 – Poster

2019 – Determining the defensive mechanisms in Green Ash (Fraxinus pennsylvanica) resistant to Emerald Ash Borer (Agrilus planipennis) – CBBI Symposium Oral Presentation, CBBI Seminar presentation – Oral