Source: VIRGINIA POLYTECHNIC INSTITUTE submitted to NRP
CHEMICAL MECHANISMS OF INSECT RESISTANCE IN APPLES
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
AFRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
1013336
Grant No.
2016-67012-26912
Cumulative Award Amt.
$23,274.87
Proposal No.
2017-05060
Multistate No.
(N/A)
Project Start Date
Feb 1, 2017
Project End Date
Jan 31, 2019
Grant Year
2017
Program Code
[A7201]- AFRI Post Doctoral Fellowships
Recipient Organization
VIRGINIA POLYTECHNIC INSTITUTE
(N/A)
BLACKSBURG,VA 24061
Performing Department
Biological Sciences
Non Technical Summary
It is well known that plants produce a diversity of chemical compounds that function as a deterrent to insect pests. Chemical compounds with potential defensive roles are produced in all plant tissues, but most studies of plant chemical defense have focused on leaves. Relatively few studies have examined whether fruit chemistry in either wild or domestic plants can function as a defense against fruit-feeding insect pests. Fruit defenses against insects may include direct defenses, such as toxins in fruit pulp that deter insect ovipoisition and feeding, or indirect defenses, such as volatile compounds released by fruits that attract the predators and parasites of insect herbivores. Apples produce a diversity of both volatile and non-volatile secondary metabolites that could function in defense, but their effects on herbivores and natural enemies are almost entirely unexplored. Furthermore, nothing is known about how apple chemical defenses may have been altered during domestication. The proposed research will use chemical analyses, experiments with insects, and field surveys to examine how apple fruit chemistry mediates resistance to fruit-feeding insects. The specific objectives are to: 1) Characterize fruit volatile and phenolic profiles and their relationship to herbivore resistance across 50 wild and 50 domestic apple genotypes; 2) Examine how apple domestication and breeding focused on increased fruit size might influence fruit defense; and 3) Determine whether direct or indirect fruit chemical defenses can be induced to decrease subsequent herbivore damage. Given that insecticides cost US farmers over $4.3 billion annually, understanding and harnessing natural fruit defenses could be a promising tool to increase the economic and environmental sustainability of apple production. The project fits well with the NIFA Priority Area 1 (plant health and production and plant products), and in particular with Sub-priority 4 (plant-pest interactions).
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
20611101070100%
Knowledge Area
206 - Basic Plant Biology;

Subject Of Investigation
1110 - Apple;

Field Of Science
1070 - Ecology;
Goals / Objectives
The overall goal of this project is to understand the chemical ecology of interactions between fruits and fruit herbivores in wild and domesticated apple. This broad goal is being addressed through the following three specific objectives:Characterize variation in fruit chemical defense and its relationship to herbivore resistance in wild and domesticated apples.Examine how apple domestication and breeding have affected fruit defense.Test whether apple chemical defenses are induced in response to herbivore damage.
Project Methods
Work remaining on the project is primarily related to Objective 3, which is to determine if induced responses to herbivore damage can lead to changes in fruit chemistry and resistance to subsequent attack. Field work related to this objective is already complete and involved a large field experiment with four varieties of domesticated apples in an experimental orchard in Geneva, NY. We established three different treatment regimes that werereplicated on 10trees per treatment per variety (120 trees total). The three treatments were: 1) Herbivore Damaged--at least 5apples per tree weredamaged by caging codling moth larvae onto fruit; 2) Phytohormone--at least 5apples per tree were treated with a synthetic analogue of jasmonic acid, a plant hormonal elicitor that often initiates and regulates induced responses to herbivores; and 3) Undamaged Control--apples were treated identically but no treatments applied. One week following these treatments, Imeasured fruit volatile organic compounds (VOCs) in situ, and collected fruits for analysis of phenolic metabolites. In addition, I collected fruits for use in a series of bioassays with codling moth in the laboratory that measured oviposition preference, larval performance, and larval survival. Fruit volatile samples were analyzed using GC/MS and fruit phenolics were analyzed using HPLC. For phenolic analyses, fruits were divided into subsamples of skin, pulp, and seeds. These chemical analyses are complete, but both created large volumes of raw chromatographic data that must be processed prior to any statistical analyses.Work remaining for this objective involves processing of 120 GC/MS chromatograms and 360 HPLC chromatograms from the previously collected chemical data. Each chromatogram can contain 10s to 100s of peaks, each of which corresponds to an individual compound. We are taking a non-targeted approach that involves classifying and integrating each peak. Once these chromatograms are prcoessed, the data will then be analyzed using machine learning algorithms to understand how chemical traits change during induction and relate to herbivore resistance.Results will then be prepared for publication in peer-reviewed journals.

Progress 02/01/17 to 01/31/19

Outputs
Target Audience:1. Other scientists working in areas of ecology, evolutionary biology, agroecology, and pest management. This audience was reached primarily through scientific publications, seminars, and conference presentations. 2. Undergraduate students in courses taught by the PI or working directly in the lab as research assistants. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided extensive training opportunities for PD Whitehead, who was supported as a post-doctoral fellow on the grant. She received outstanding mentorship in the research areas of agricultural ecology, evolutionary ecology, entomology, and integrated pest management from Katja Poveda, Art Agnello, and many other facultyat Cornell University. Their research mentorship, as well as the extensive professional development opportunities provided at Cornell,helped propel PD Whitehead into a faculty position at Virginia Tech, where she is currently an Assistant Professor in the Department of Biological Sciences. In addition, the project provided research training for five research technicians (at the post-baccalaureate stage), several of whom have now continued on to graduate programs, and 9 undergraduate students who assisted with field and lab work related to the project.Students have learned valuable skills in experimental design, field sampling of plants for insect damage and chemistry, and laboratory skills such as the analysis of plant secondary metabolites using high-pressure liquid chromatography (HPLC) and post-processing of chromatograms. How have the results been disseminated to communities of interest?Results have been disseminated to the scientific community through peer-reviewed publications, conference presentations, invited seminars, and informal discussions. In addition, results have been disseminated to undergraduate students through direct participation in the project and through the use of this project as a classroom example for Dr. Whitehead's course in Ecology (140 students Fall 2017, 75 students Spring 2018). Finally, results have been communicated togrowers and industry professionals informally through conference presentations, discussions, and other direct communication. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? It is well-known that plants produce chemical compounds as a defense against insect pests. However, the diversity of different compounds produced is bewildering, and, for most plants, little is known about the specific chemical mechanisms of defense. In crop plants, an improved understanding of these mechanisms can provide new tools for management of major pests. This project has provided detailed analyses of the phenolic metabolites produced in skin, pulp, and seeds of apples and how these compounds function in defense against a major fruit-feeding pest, the codling moth. The codling moth can reach devastating levels in orchards worldwide if not properly controlled, and our results can lay a foundation for new strategies that can minimize pesticide use on one of the most consumed fruits. More broadly, this project is informing our understanding of how the process of domestication can alter plant defenses. This has been accomplished through comparisons of chemistry and resistance in wild and domesticated apples as well as a larger synthesis of published data across 83 crops. This work can inform breeding practices aimed at maximizing yield while still maintaining high levels of natural defenses that help protect plants in natural ecosystems. Related to goal #1, we conducted detailed analyses of phenolics and codling moth resistance across 56 genotypes of domesticated apples and 52 genotypes of wild apples. We found strong variation in resistance, and overall resistance increased with increasing phenolic diversity. Resistance was not related to total phenolic concentration, but several individual compounds, primarily flavan-3-ols, were related to increased herbivore resistance. These results are summarized in our paper that was published in Annals of Botany in 2019. In addition, this project led to a related project that involved a mechanistic experiment to determinethe effects of phenolic diversity on insect performance. We found that chemical diversity provides an adaptive benefit to plants by defending against multiple different herbivores simultaneously. All data collection for this study is complete and we are currently preparing results for publication. We expect that this will be published by the end of 2019. Related to goal #2, we used data collected for goal #1 to also assess how domestication has affected apple chemistry and resistance. We found that domesticated apples have much lower concentrations and lower phenolic diversity relative to their wild ancestor, Malus sieversii. By examining apples across a large gradient of fruit sizes, we also found that the loss of defenses may be explained in large part by selection for increased yield. These results are also summarized in our Annals of Botanymanuscript (Whitehead and Poveda 2019). In addition, we have completed a larger meta-analysis of the effects of domestication on herbivore resistance and plant defense traits, and this was published in a special issue of PTRSB (Whitehead et al. 2017). Finally, we have also more broadly summarized the implications of domestication for agroecology and society in a review paper, also published in PTRSB (Turcotte et al. 2017). Related to goal #3, we have completed a large field experiment that examined how fruit damage by the codling moth or treatments with a hormonal elicitor can influence fruit chemistry and subsequent resistance. The field work was completed during the summer of 2015, chemical analyses of samples usinghigh-pressure liquid chromatography (HPLC) and all of the related post-processing of chromatographic data was completed in 2018. Data from the bioassays and field surveys of damage conducted in 2015 do indicate that there is an induced response to herbivore damage in apple fruits, with resistance increased in previously damaged fruits. We are currently conducting statistical analyses of data and expect to submit a manuscript summarizing these results by the end of 2019.

Publications

  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Whitehead, Susan R., and Katja Poveda. Resource allocation trade-offs and the loss of chemical defences during apple domestication. Annals of botany (2019). doi.org/10.1093/aob/mcz010
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Effects of phytochemical diversity on insect performance; Organized Oral Session, Ecological Society of America Annual Meeting, New Orleans, LA
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: Crop domestication and the defense of fruits against insect herbivores; invited seminar, USDA-ARS, Appalachian Fruit Research Station, Kearneysville, WV
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: The Adaptive Significance of Phytochemical Diversity in Herbivore Defense; Contributed Poster, Gordon Conference for Plant-Herbivore Interactions, Ventura, CA
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Harnessing Plant Induced Defenses for Improved Pest Management in Apples; invited presentation, Entomological Society of America Eastern Branch Meeting, Blacksburg, VA


Progress 02/01/17 to 01/31/18

Outputs
Target Audience:1. Other scientists working in areas of ecology, evolutionary biology, agroecology, and pest management. This audience wasreached primarily through scientific publications, seminars, and conference presentations. 2. Undergraduate students in courses taught by the PIor working directly in the labas research assistants. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has primarily provided training for Annie Zell, a technician working on the project, and Alexandra Corrigan, an undergraduate research assistant. Both have learned valuable new skills in the analysis of plant secondary metabolites using high-pressure liquid chromatography (HPLC) and post-processing of chromatograms. How have the results been disseminated to communities of interest?I have communicated results to growers and industry professionals informally through discussions and other direct communication. In addition, the results of this work have been presented in my own Fall 2017 classroom to 140 students in sophmore-level Ecology. What do you plan to do during the next reporting period to accomplish the goals?The next reporting period will focus on finalizing the chemical analyses associated with goal #3 and preparing these results for publication. Annie Zell, the current technician in my lab, will continue to work on this project. In addition, I will complete revisions and finalize the major paper coming from our work in apples related to goals #1+2. Finally, I will be starting to analyze data from another project that grew out of goal #1, which involved an experimental approach to understanding how the diversity of phenolics in fruit may help provide more effective defense against pests.

Impacts
What was accomplished under these goals? It is well-known that plants produce chemical compounds as a defense against insect pests. However, the diversity of different compounds produced is bewildering, and, for most plants, little is known about the specific chemical mechanisms of defense. In crop plants, an improved understanding of these mechanisms can provide new tools for management of major pests. This project has provided detailed analyses of the phenolic metabolites produced in skin, pulp, and seeds of apples and how these compounds function in defense against a major fruit-feeding pest, the codling moth. The codling moth can reach devastating levels in orchards worldwide if not properly controlled, and our results can lay a foundation for new strategies that can minimize pesticide use on one of the most consumed fruits. More broadly, this project is informing our understanding of how the process of domestication can alter plant defenses. This has been accomplished through comparisons of chemistry and resistance in wild and domesticated apples as well as a larger synthesis of published data across 83 crops. This work can inform breeding practices aimed at maximizing yield while still maintaining high levels of natural defenses that help protect plants in natural ecosystems. Related to goal #1, we conducted detailed analyses of phenolics and codling moth resistance across 56 genotypes of domesticated apples and 52 genotypes of wild apples. We found strong variation in resistance, and overall resistance increased with increasing phenolic diversity. Resistance was not related to total phenolic concentration, but several individual compounds, primarily flavan-3-ols, were related to increased herbivore resistance. These results are summarized in our paper that was recently submitted to Journal of Ecology. Related to goal #2, we used data collected for goal #1 to also assess how domestication has affected apple chemistry and resistance. We found that domesticated apples have much lower concentrations and lower phenolic diversity relative to their wild ancestor, Malus sieversii. By examining apples across a large gradient of fruit sizes, we also found that the loss of defenses may be explained in large part by selection for increased yield. These results are also summarized in our Journal of Ecology manuscript. In addition, we have completed a larger meta-analysis of the effects of domestication on herbivore resistance and plant defense traits, and this was published in a special issue of PTRSB (Whitehead et al. 2017). Finally, we have also more broadly summarized the implications of domestication for agroecology and society in a review paper, also published in PTRSB (Turcotte et al. 2017). Related to goal #3, we have completed a large field experiment that examined how fruit damage by the codling moth or treatments with a hormonal elicitor can influence fruit chemistry and subsequent resistance. The field work was completed during the summer of 2015 and we are still working to complete all chemical analyses using high-pressure liquid chromatography (HPLC) and all of the related post-processing of chromatographic data. Data from the bioassays and field surveys of damage conducted in 2015 do indicate that there is an induced response to herbivore damage in apple fruits, with resistance increased in previously damaged fruits.

Publications

  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Whitehead, S.R., M. M. Turcotte, and K. Poveda (2017). Domestication impacts on plant-herbivore interactions: a meta-analysis. Philosophical Transactions of the Royal Society B 372 (1712): 20160034
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Turcotte, M.M., H. Araki, D.S. Karp, K. Poveda, and S. R. Whitehead (2017). The eco-evolutionary impacts of domestication and agricultural practices on wild species. Philosophical Transactions of the Royal Society B 372 (1712): 20160033
  • Type: Journal Articles Status: Under Review Year Published: 2018 Citation: Whitehead, S.R., and K. Poveda (in review). Resource-allocation trade-offs and the loss of chemical defenses during apple domestication. Journal of Ecology
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Whitehead, S.R. The Chemical Ecology of Fruit Defense in Apples Virginia Tech Department of Entomology Invited Seminar
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Whitehead, S.R. Crop Domestication and Plant-Insect Interactions Virginia Tech Department of Horticulture Invited Seminar
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Whitehead, S.R., Ethan Bass, Andre Kessler, and Katja Poveda, Effects of phytochemical diversity on insect performance, Association for Tropical Biology and Conservation, Merida, Mexico