Recipient Organization
TEXAS A&M UNIVERSITY
750 AGRONOMY RD STE 2701
COLLEGE STATION,TX 77843-0001
Performing Department
Plant Pathology & Microbiology
Non Technical Summary
Our valuable natural forests and urban trees are under a barrage of emerging and introduced tree pathogens. This is particularly true in Texas where the enormous value of these resources are subject to extremely stressful climates and a continual invasion of exotictree pathogens acrosslengthy borders. Solutions to the diseases areas complex as the pathogens themselves, the tree hosts they infect and the diseases they cause. There is relatively little research currently being conducted to provide practical, effective options for directly managing tree pathogens and mitigating thier impacts. This is particularly obvious when interacting with clientele expecting some useful response from AgriLife Extension when they reach out for solutions to their tree problems in Texas. Improvements in early detection and diagnostics would be very helpful, because these issues are the first line ofdefense against any plant pathogen. For improving plant disease diagnosis, studies to develop a RT-PCR protocol for detecting the oak wilt pathogen, Bretziella fagacearum will be conducted in this proposed M-S project. There are several limitations to the most common method for diagnosing a tree suspected of being infected with oak wilt. This method relies on growing the fungus out of the sample in the laboratory, and can take weeks to complete and may have unacceptably high levels of false negative results (the tree may be infected but the sample does not contain the fungus). An RT-PCR method will be quicker and far more sensitive than isolating the pathogen, but requires a great deal of effort to verify the reliability and consistency of the test. Another potential advantage would the ability to successfully conduct a post mortum on diseased trees to diagnose a case of oak wilt after it the tree has died.The other issue, concerning the monitioring of exotic pathogens, will also be a focus of the proposed project There will be surveys for Citrus Greening, caused by a bacterium called Candidatus liberabacter asiaticus, and Sudden Oak Death, caused by the fungus Phytophthora ramorum. These two pathogens pose an immediate and significant threat to tthe Texas citrus industry as well as the considerable oak resources of the State. Another important issue that will be addressed is the need for improvements to methods ofdirect control and saving trees at threat of infection by the oak wilt pathogen. Tree injection with a fungicide has proven to be an effective option in the management of oak wilt. One technique, called the macro-injection method, has dominated the injection market for the past 20 years because there were reliable research results to support its use. More recently, there has been a proliferation of new methods for injecting trees, mostly based on "micro" injection methods. These new methods are purportedly faster, less laborius, and better for the tree than macroinjection. However, the only evidence to support these claims is in need of further verification and testing. That is another objective of this project, to test methods of injecting trees with both systems under conditions of natural infection by the pathogen to determine whether the advantages and disadvantages to how trees are currently being injected. The information generated by the proposed studies will be of great interest to a wide variety of clientele in both the public and private sectors. One of the greatest impacts will be on the Central Texas urban forests where there is a thriving, well - trained and organized arborilogical industry in Texas ready to adopt better technology for dealing with oak wilt. The PI regularly meets with arborists and homeowners at 25 - 30 meetings annually, including several Master Gardener trainings in Texas counties. Factsheets will be published through the Texas A&M AgriLIfe Bookstore for distribution on the internet, and there will publications in peer-reveiwed journals for the braoder scientific community.
Animal Health Component
80%
Research Effort Categories
Basic
10%
Applied
80%
Developmental
10%
Goals / Objectives
The value of trees to the State of Texas can be expressed in many ways. The total economic output of the East Texas forest timber industry in 2015 was $29,849,220,000. Timber alone was ranked ninth among Texas' top ag commodities and forest based industry was one of the top 10 manufacturing sectors in the state (see website http://txforestservice.tamu.edu/main/default.aspx). Although more difficult to quantify, the urban forest values in the state are also considerable. For example, a recent study by the U.S. Forest Service revealed that the compensatory value of trees in Austin, TX, in terms of air pollution removal, reduced carbon emissions, carbon storage and sequestration, reduced energy use for buildings, storm water capture, etc., was $16 billion. Similar staggering values can be found for Houston, San Antonio, Dallas, and other metropolitan areas throughout the state. However, economic values do not tell the whole story as far as the value trees have to the state in terms of value of life and ecosystem services. For example, live oak (Quercus virginiana, Q. fusiformis) is represented on the original state seal of Texas, going back to 1845, as a symbol of strength and endurance. This connection with live oak was most recently exemplified by the national recoginition of the iconic Goose Island Oak near Rockport, TX, when it survived a direct strike by Hurricane Harvey. The trees of Texas are economic and environmental assets that justify the effort to better protect them from the ravages of pathogenic agents.A wide variety of forest types and woodlands occurs in Texas (Correll and Johnston 1970, also see website of the Bureau of Economic Geology, University of Texas http://www.beg.utexas.edu/UTopia/images/pagesizemaps/vegetation.pdf). There are therefore many different species of trees, each with its complement of diseases. Some diseases are caused by existing, infectious pathogens with the potentials to cause extremely destructive epidemics, such as oak wilt and Dutch elm disease. Other diseases appear to be less pathogenic, but are increasing in incidence and severity with changes in climatic conditions (Kliejunas et al. 2009). Also, the introduction of exotic, invasive pathogens on trees is an ongoing threat in Texas, with the potential for a huge impact on valuable landscape and forest trees (Tkacz et al. 1998, Hulcr and Dunn 2011).Monitoring and studying tree diseases, regardless of their origins, are warranted when they threaten the extremely valuable Texas woodlands, forests, and urban landscapes. This project addresses those threats with better detection, improved understanding of their epidemiology, and the ultimate goal of reducing their impact. New and refined disease prevention and control methods resulting from these studies will be made available through educational outreach activities to the vast clientele of the Texas A&M AgriLife Extension Service. These research goals are consistent with the emerging knowledge areas, as defined in the 2010 McIntire-Stennis Strategic Plan update. Specifically, in the first of two recommendations, pathogens are specifically cited in the Foundational Areas of Knowledge as a focus of research. A fundamental understanding of pathogen function is ".....critical to achieving a broader knowledge of forests, watersheds, and global functions." In addition, technological advancements are needed in areas such as nanotechnology, remote sensing, and biotetchnology in order to monitor, assess, and expand the productivity and utility of forests. The advancement and application of new state-of-the-art technologies will advance our capacity to protect forests.Given the high value of trees as a critical natural resource, and given the existing disease threats to that resource, the major goals of this project are to: I. Identify and assess the disease threats to Texas forests, woodlands, and urban forests of Texas II.Improve existing methods to control or manage disease threates to Texas forests, woodlands, and urban forests. III. Disseminate project activities and results to relevant audiences.
Project Methods
ProceduresObjective I. Identify and assess the disease threats to Texas forests, woodlands, and urban forests of Texas. Approach. The surveillance of tree diseases can be accomplished through a number of means. Given the need to cover such a large area, a hierarchical approach must be used to gather data at different scales. County Extension Agents with Texas AgriLife Extension and their volunteers, such as the Master Gardeners and Master Naturalists, will be trained to assist with statewide monitoring for new and emerging pathogens. Training of arborists, landscape professionals, nurserymen, and natural resource managers through workshops, websites (i.e., www.texasinvasives.org), and various educational outputs will also be an effective strategy to alert practitioners of threats. At a finer scale, there are prescribed survey protocols for detection of exotic pathogens with suspected routes of entry. In the case of SOD, surveys will focus on locations where the pathogen was previously found. Off-site, streamside surveys will consist of baiting waterways downstream from the sites and processing the baits for detecting P. ramorum in the lab (see the Forest Health Monitoring website http://www.fhm.fs.fed.us/sp/sod/sod.shtml). In addition, the same locations will undergo on-site soil and water sampling (see website of USDA APHIS PPQ website http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/ for the latest protocols). For the detection of citrus greening, the focus will be on the Asian citrus psyllid, Diophorina citri Kuwayama, since the pathogen has yet to be found in Texas. Dooryard and landscape citrus trees will be sampled for psyllids and suspect tissues exhibiting symptoms of greening. Appropriate sampling locations will be provided by Master Gardeners, Master Naturalists, County Extension Agents, and urban foresters. These samples will be returned to the Texas Plant Disease Diagnostic Laboratory for detection of C. l. asiaticus using prescribed molecular protocols (see website of the USDA APHIS http://www.aphis.usda.gov/plant_health/plant_pest_info/citrus_greening/index.shtml). Citrus canker is another introduced bacterium with the potential for economic impact on the the greater commercial citrus industry in South Texas, and must be monitored throughout the Upper Gul Coast dooryard citrus population (Gottwald, T.R. 2000. Citrus canker. The Plant Health Instructor. DOI: 10.1094/PHI-I-2000-1002-01).Objective II. Improve existing methods to control or manage disease threats to Texas forests, woodlands, and urban forests.Part 1. Test and adopt new tools to diagnose oak wilt in a clinical setting. Approach.Each phase in the diagnostic process using qPCR to detect Bretziellla fagacearum (formally known as Ceratisistis fagacerarum) for clinical testing will be examined. Sapwood samples will be collected from infected and non-infected live oaks (Quercus fusiformis) in Central Texas for detection utilizing the standard culturing technique and comparing those results to testing with qPCR. The samples will be processed in the Texas Plant Disease Diagnostic Laboratory (TPDDL), Texas A&M AgriLife Extension Service in College Station, TX. The samples will be extracted using various extraction methods and specific probes and primers will be used for qPCR with an Applied Biosystems® 7500 Real-Time PCR System (Applied Biosystems Inc., Foster City, CA). Sample collection will vary according to season, Quercus sp., degree of symptom development in diseased trees, geographic location, sample retrieval and handling, and other factors that might vary during the course of submission to the TPDDL.Part 2. Test new injection protocols for treating high risk oaks threatened by infection by the oak wilt pathogen. Approach. The study is being conducted in central Texas within untreated, expanding oak wilt centers on privately-owned property within the range of live oak and oak wilt in central Texas. Non-symptomatic test trees (~125), ranging from 15 to 46 cm (6 - 18 in) dbh (diameter at breast height), will be selected in proximity with trees showing oak wilt symptoms (veinal necrosis). In April 2016, fifty (50) trees per delivery system (10 trees per site in five different sites) were injected with Alamo® (Syngenta) at the label rate (20 ml/inch tree dbh) using the two systems described above. A minimum of twenty-five (25) trees (5 trees per study site) serve as untreated controls. The application procedure used to inject the propiconazole formulation is based on the recommendations of each system manufacturer. All of the injected or check trees are located adjacent to the infected trees, at a distance of at least 50 - 75 ft but exhibiting no symptoms of oak wilt infection. The treatments are therefore being tested under conditions of natural infection with the pathogen. Trees have been evaluated for oak wilt symptoms at 6 month intervals since the treated. Each tree crown is given a rating of 0 (healthy), 1 (wilt symptoms comprising up to one-third of the crown), 2 (wilt symptoms comprising greater than one-third of the crown) (Mayfield et al. 2008), or 3 (dead tree). At each rating period, trees with a crown rating of 2 may be sampled from the stem and branches to determine the presence of Ceratocystis fagacearum. At the termination of the experiment in June 2019, final crown ratings will be made. An analysis of variance will be used to test for differences among injection systems. A X2 (Chi-square) test for homogeneity will be used to test the null hypothesis that the percentage of trees with a crown rating of 2 did not differ between the fungicide-treated trees and the untreated control group (Mayfield et al. 2008). The null hypothesis will be rejected if more than 20% of the fungicide-treated trees reached a crown rating of 2. The test will be invalidated if fewer than 60% of the control trees reach a crown rating of 2.Objective III. Disseminate project activities and results to all relevant audiences throughout Texas. Approach. The target audience(s) correspondwith each of the outcomes of this project. Information generated from the project is disseminated through many diverse county programs usually involving homeowners and landowners. The PI usually has direct contacts with 1,000 to 1,500 participants in these county programs, sponsored by the Texas A&M AgriLife County Extension Agents. Other audiences includenatural resource managers, ranch managers, and master gardeners. All of these groups are trainers and serve to deliver high quality, technically based information on the identification, biology and control of tree diseases. The groups are reached through a variety of trainings, workshops, and invited presentations sponsored by TAMU AgriLife, the Texas Forest Service, the Texas Chapter of the International Society of Arboriculture, and other entities. The PI also has a teaching appointment and is responsible for two courses where the information generated by this project are presented. These include ESSM 307 Forest Protection, and PLPA 301 Plant Pathology.