Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
Entomology
Non Technical Summary
It is well knownthat plants produce a diversity of chemical compounds thatfunction as a deterrent toinsect 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 fruitchemistry 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)
Goals / Objectives
Research GoalsCharacterize variation in fruit chemical defense and its relationship to herbivore resistance in wild and domesticated apples I will combine field surveys, laboratory bioassays with focal insect herbivores, and analyses of fruit secondary metabolites across 50 wild genotypes and 50 domesticated varieties to examine how fruit chemistry shapes resistance to insect herbivores. Examine how apple domestication and breeding have affected fruit defense. I will use the chemical and ecological datasets generated for Objective 1, combined with existing genetic data, to conduct phylogenetically-controlled analyses that examine how domestication and selection for increased fruit size have affected fruit defense.Test whether apple chemical defenses are induced in response to herbivore damage. I will conduct experiments with four domestic apple varieties to test whether damage from fruit herbivores causes changes in: a) fruit secondary metabolites b) resistance to subsequent damage in the field, c) the preference and performance of focal insect herbivoresTraining/Career Development GoalsDevelop theoretical background and practical skills in agricultural ecology. The proposed research departs from my doctoral work in that it focuses on a domesticated species in an agricultural ecosystem. Thus, my primary training objectives are to: a) increase my theoretical understanding of how ecological and evolutionary processes operate in an agricultural context, and b) develop a practical skill-set in agricultural research methods.Develop productive collaborations across disciplines.I will interact regularly with the Cornell Chemical Ecology Group, a consortium of 22 faculty from eight departments. I will meet diverse researchers within and outside Cornell at several national meetings and through weekly seminar series in Entomology, Ecology and Evolutionary Biology, and Plant Biology. At NYSAES, I will interact with the large group of researchers working on apples as well as stake-holders in the apple industry.Gain experience and develop proficiency in teaching and mentoring. Over the course of the Fellowship, I will hone my skills as an educator by serving as a guest instructor for short modules (2-3 lectures or activities) in existing courses taught by Dr. Poveda and other Cornell faculty.In addition to classroom teaching, I willdirectly mentor undergraduate students as research assistants (4-6 students per year) and for independent projects (1-2 students). Finally, I will take advantage of the enormous resources provided by the Cornell Center for Teaching Excellence (CTE), such as monthly workshops, consultations, and classroom observations. Gain experience and develop proficiency in research communication.I will expand my proficiency inresearch communicationwith stakeholders in agriculture and the general publicthrough collaboration with extension scientists, particularly Art Agnello (Collaborating Mentor), and extension activities such as monthly meetings with growers at NYSAES and publication of research summaries in extension publications.
Project Methods
Objective 1:In order to understand the relationship between fruit chemistry and resistance in wild and domesticated apples, I will conduct chemical analyses, field damage surveys, and bioassays with 50 domestic genotypes (i.e. varieties) of M. x domestica and 50 genotypes of M. sieversii, utilizing the same genotypes included in the preliminary study described above. At five time points over the course of fruit development in summer/fall 2016, I will conduct field surveys of each tree to quantify damage from all major insects present in orchards. Surveys will be conducted using monitoring protocols established by Art Agnello (Collaborating Mentor). At two points during the growing season, I will sample volatiles from all trees in situ using dynamic headspace techniquesand collect 20 fruits per tree, always sampling from various parts of the tree with different sun exposures and heights to obtain a representative sample. From the 20 fruits, 5 will be randomly chosen for chemical analyses, and 15 will be used for laboratory bioassays with pests such as the apple maggot (5 fruits), codling moth (5 fruits), and/or plum curculio (5 fruits). For each insect species, bioassays will involve placing a group of 15 newly emerged pairs of adult insects into a container with 5 fruits and allowing them to oviposit over a period of 1-5 days (depending on the species). I will record the number of eggs laid (codling moth) or punctures to the fruit surface that typically contain single eggs (for apple maggot and plum curculio). The infested fruits will then be incubated to allow larval development and I will record larval survival rates, time to pupation, pupal weights, and adult emergence rates. These measures will provide a detailed picture of fruit resistance to each of the insect species.Volatile samples collected from each fruit will be analyzed with gas chromatography combined with mass spectrometry (GC-MS) using previously described methods. For the phenolic analyses, fruits will be separated into skin, pulp, and seed, freeze-dried, and analyzed using established methods of phenolic extraction and quantification using HPLC. All analyses will be conducted at the Cornell Chemical Ecology Group Core Facility, which is available to anyone in the Cornell community on a user fee structure, houses all the necessary instrumentation, and employs an analytical chemist to provide technical assistance with analyses.Objective 2:The dataset generated for Objective 1 will also provide a means to test how the process of domestication and selection for increased fruit size has altered investment in plant defense. The only additional data required for this analysis will be a measure of fruit size, which is highly variable among both wild and domestic apples. I will measure fruit mass for each of the 50 domestic and 50 wild genotypes using an average from the 15 fruits per tree collected for bioassays. In addition, I will compile existing data on microsatellite variation in seven loci (available for all accessions in the collection)to build a phylogeny of the individuals in the study population. Because apples that are more closely related would be expected to be more similar both in terms of fruit size and resistance, this will allow me to control for relatedness when testing for the effects of fruit size on various defense traits.Objective 3:To determine if induced responses to herbivore damage can lead to changes in fruit chemistry and resistance to subsequent attack, I will conduct a field experiment with four varieties of domesticated apples in an experimental orchard (see Study Site). I will establish three different treatment regimes that will be replicated on 15 trees per treatment per variety (180 trees total). The three treatments will be: 1) Herbivore Damaged--at least 10 apples per tree will be damaged by caging codling moth larvae onto fruit; 2) Phytohormone--at least 10 apples per tree will be treated with jasmonic acid, a plant hormonal elicitor that often initiates and regulates induced responses to herbivores; and 3) Undamaged Control--apples will be treated identically but no treatments applied. On all trees used in the experiments, early season damage from disease or insects will be controlled using standard pesticide treatments to minimize the potential for any induction of defenses due to natural damage. Once fruits begin to develop, and coinciding with the typical egg-hatch for the first generation of codling moth in late June, I will apply herbivore damage or phytohormone treatments to fruits. Treatments will be applied on 10 fruits per tree, spread throughout the tree on different branches. For the herbivore damage treatment, five neonate codling moth larvae will be caged onto a single fruit using a fine mesh bag and allowed to feed for one week. For the phytohormone treatment, jasmonic acid will be sprayed over the fruit surface using established methods and at concentrations typical of damaged fruits (based on samples collected from the preliminary experiments described above). Bags will then be placed over the fruits to create conditions equivalent to those of the herbivore damaged fruits. Fruits on the control trees will receive bags only, with no treatment applied.I will measure the following response variables on all trees: 1) Fruit volatile induction: One week after the treatments are applied, I will sample fruit volatiles in situ from all trees. Samples from treatment (herbivory or jasmonic acid) trees will include a bagged/treated fruit, an adjacent fruit on the same branch, and a fruit from an undamaged branch. Samples from control trees will include a bagged fruit and an unbagged fruit only. These samples will be analyzed using GC/MS. 2) Fruit phenolic induction: The same fruits used for volatile sampling will be collected, divided into skin, pulp, and seeds, and immediately frozen in liquid nitrogen for phenolic analysis using HPLC. 3) Changes in codling moth preference/performance: At the same time that chemistry samples are collected, a set of similar fruits will be collected in triplicate from each tree for use in laboratory bioassays with codling moth as described for Objective 1. 4) Changes in overall resistance: I will conduct field damage surveys of all trees in the study population at one, two, four, and six weeks after the treatments, assessing damage from the natural community of herbivores as described above. 5) Changes in attraction of natural enemies. At approximately one week following damage treatments, I will place codling moths at different life stages as sentinel prey in apple trees from herbivory treated, jasmonic acid treated, and control groups. In each tree, eggs, larvae feeding inside fruits, and pupae will be left in orchards for a period of 24 hours, after which I will assess the number of eggs/larvae/pupae removed or damaged by predators. All remaining insects will be reared individually in the laboratory to determine the percentage of parasitism.