I have blogged several times about the need to enhance efforts to breed trees resistant to the most damaging of the hundreds of introduced insects and pathogens. Others concur – see reports by the National Academy of Sciences in 2018; several publications by USFS scientists Richard Sniezko and Jennifer Koch; a workshop hosted by Purdue w/ USFS support, the creation and efforts of several consortia – Whitebark Pine Ecosystem Foundation, Great Lakes Basin Forest Health Collaborative, Forest Restoration Alliance …
Also, Richard J. A. Buggs, of the Royal Botanic Gardens, Kew, recently summarized barriers to tree breeding. It was published as an especially thoughtful editorial in Plants People Planet in anticipation of the International Year of Plant Health in 2020 (see reference at the end of this blog). That issue included several related articles, also noted below.
R.J.A. Buggs’ Perspective on Tree Breeding
Buggs says the need for tree resistance research is greater than ever before. First, damage caused by introduced insects and pathogen is rising. Plus, we now recognize trees’ importance in capturing atmospheric carbon. He sees encouraging signs of growing public awareness of both factors. Also, he thinks citizen science might reduce the cost of some activities … although he doesn’t name which they are.
Dr. Buggs lists six major hindrances to breeding programs, including some aspects that I, at least, have not considered:
1) Trees’ size and long generation times mean research is necessarily slow. One result is it is hard to formulate research proposals that match funding cycles. This in turn means a dependence on long-term institutional commitment from well-funded organizations, and such institutions are rare.
I point out that the U.S. government – especially the USFS – is one such institution. Unfortunately, it has so far been reluctant to take commit major resources to breeding pest-resistant trees. Every year I urge you to lobby Congress on appropriations for the agency. In this context, do you understand that while the USFS Research budget receives approximately $300 million each year, less than $5 million of that total is allocated to researching invasive species (of all taxa)? Some gaps are filled by projects funded by the Forest Health Program. You will have a new opportunity to lobby Congress for Fiscal Year 2023 in the spring!
2) On the other hand, reliance on long-term institutional funding shelters projects from multidisciplinary peer-review that could introduce improved technology or methods. This lack of peer review also contributes to a perception among other scientists that tree resistance research is a scientific backwater.
3) Similarly, studies requiring a long time horizon don’t fit publication schedules. Again, the result is that the findings often appear only in institutional reports or conference proceedings. This means they are hard to find and often lack external peer review at not only the proposal stage but also before publication.
4) The long decades without clear success in dealing with Dutch elm disease (but see recent encouraging developments here) and chestnut blight (see The American Chestnut Foundation here) gave the impression that resistance breeding of forest trees is impossible. Buggs says pest resistance problems are easier to tackle for other trees.
5) Those considering what efforts to fund might demand complete resistance to the pest. This goal is not only unrealistic – it is often unnecessary. Often lower levels of resistance or tolerance can result in trees that can be self-sustaining. Dr. Sneizko concurs; see his article appearing in this issue.
6) Forest stakeholders differ over the goal of developing resistant trees. Some think any human intervention is unwarranted in wilderness areas. Some want a tree as similar as possible to pre-epidemic trees. Others want a tree that produces more timber.
Other Significant Articles
A second article in the same issue of Plants People Planet (Federman and Zankowski) discusses the USDA’s commitment to new approaches in tree resistance research.
I found a third article that discusses British approaches to mitigating tree pests to be more informative than Federman and Zankowski – although somewhat worrying. Spence, Hill and Morris praise the U.K.’s Plant Health Risk Register, which they say has enhanced vigilance on possible new pest introductions. However, the authors describe resistance breeding as a strategy to be considered “when a pest has established such that a tree population is unable to recover, and where a genetic basis for resistance is demonstrable in a proportion of the tree population.” Dr. Sneizko, and others – and I! – call for initiating exploration of the potential for resistance breeding much earlier in an invasion.
A fourth article – by Richard Sniezko and colleagues — describes encouraging levels of partial resistance to white pine blister rust in two western white pines and evidence for both qualitative and quantitative resistance to Phytophtohora lateralis in Port-Orford Cedar.
A fifth – by Showalter et al. — reports encouraging levels of resistance to both emerald ash borer DMF and ash dieback in European ash. The authors conclude that a breeding program might be a viable solution to both pests.
SOURCE
Special issue of Plants People Planet for 2020 — the International Year of Plant Health. https://nph.onlinelibrary.wiley.com/toc/25722611/2020/2/1
Posted by Faith Campbell
We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.
For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm
My question is not about the resistance breeding itself, but what happens after the disease-resistant tree is developed. Reintroducing a resistant tree throughout its original habitat and re-establishing its ecological role would take many decades for any long-lived species if there were a massive planting effort, and would take centuries if the tree were left to disperse on its own. I don’t know of any example where this re-establishment process has even begun on any reasonable scale. Do we really expect the government to support a decades-to-centuries long re-establishment effort? And if not, what is the point of resistance breeding for “wild” trees? And would the funds spent on that research and deployment be better spent on prevention, surveillance and biocontrol efforts, while allowing natural selection to do the “resistance breeding” for trees in the wild?
The situation is different for trees in highly managed environments like plantations, orchards and city streets. Trees used in those settings are re-planted at regular intervals, and we could expect that resistant varieties would be useful.
Gary, I agree that those are real issues. I hope that citizen groups would help with the planting – and tending! of resistant propagules. I just don’t want to give up on the dozens of tree species already hammered by pests. Perhaps — maybe — the emphasis on tree planting to counter climate change might offer some support for these actions [note how many caveats!].
Of course I do support increased resources devoted to prevention, surveillance, and measures aimed at the invading organism – including biocontrol. Most of these work even more poorly on pathogens …
Faith: I certainly agree with you about not giving up, and the vision of an army of citizen tree planters carrying disease-resistant seedlings into the forest is certainly appealing, but I don’t know how realistic it is. Most seedlings in a forest don’t make it, especially in a world with overabundant deer.
I know of places where chestnut is the main understory tree in the forest, but the trees die from the blight when they get to about 10-15 feet tall. If the blight fungus were controlled, these areas would be chestnut-dominant forests in 20 years or so. There is some effort on biocontrol of chestnut blight
(https://acf.org/ct/news-and-updates/a-brief-summary-of-chestnut-canker-biocontrol/ )
but obviously a lot of work needs to be done.
In the western US we have many opportunities to plant forest trees due to large wildfires. Sniezko and others live in that part of the country and they have been working on species for which openings occur.
By introducing resistant trees (say to white pine blister rust) those genes can also spread naturally through the population. Yes, it does take a while (pines produce seed at 30-40 years?), but if you’re planting anyway..
I agree that in the east where there are no fires, it’s a tougher thing to do. But people like to plant and protect American chestnut trees on their own or others’ land. As you said it’s unlikely that that will “reestablish its ecological role” but can provide species diversity and perhaps some resilience to climate change. Perhaps with climate change all “ecological roles” will have to change.