Browsing by Author "Whitehead, Susan R."

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    Aggregation Pheromone Biosynthesis and Engineering in Plants for Stinkbug Pest Management
    Lehner, Bryan W. (Virginia Tech, 2019-04-26)
    Stinkbugs (Pentatomidae) and other agricultural pests such as bark beetles and flea beetles are known to synthesize terpenoids as aggregation pheromones. Knowledge of the genes and enzymes involved in pheromone biosynthesis may allow engineering of pheromone biosynthetic pathways in plants to develop new forms of trap crops and agricultural practices for pest management. The harlequin bug, Murgantia histrionica, a specialist pest on crucifer crops, produces the sesquiterpene, murgantiol, as a male-specific aggregation pheromone. Similarly, the southern green stink bug, Nezara viridula, a generalist pest worldwide on soybean and other crops, releases sesquiterpene cis-/trans-(Z)-α-bisabolene epoxides as male-specific aggregation pheromone. In both species, enzymes called terpene synthases (TPSs) synthesize precursors of the aggregation pheromones, which are sesquipiperitol and (Z)-α-bisabolene as the precursor of murgantiol and cis-/trans-(Z)-α-bisabolene epoxide, respectively. We hypothesized that enzymes in the family of cytochrome P450 monooxygenases are involved in the conversion of these precursors to the final epoxide products. This study investigated the tissue specificity and sequence of these conversions by performing crude enzyme assays with protein extracts from male tissues. Furthermore, candidate P450 genes were selected by RNA-sequencing and co-expression analysis and the corresponding recombinant proteins tested for enzyme activity. To engineer the pheromone biosynthetic enzymes in plants, transient expression of the TPSs of both stink bugs was performed in Nicotiana benthamiana leaves. Both sesquipiperitol and (Z)-α-bisabolene were found to be produced and emitted from inoculated N. benthamiana leaves. Future work will implement stable transformation to engineer murgantiol biosynthesis in crucifer trap crops and develop similar approaches for pheromone engineering of other agricultural pests.
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    Ants disperse seeds farther in habitat patches with corridors
    Burt, Melissa A.; Resasco, Julian; Haddad, Nick M.; Whitehead, Susan R. (Wiley, 2022-12)
    Habitat fragmentation impacts ecosystems worldwide through habitat loss, reduced connectivity, and edge effects. Yet, these landscape factors are often confounded, leaving much to be investigated about their relative effects, especially on species interactions. In a landscape experiment, we investigated the consequences of connectivity and edge effects for seed dispersal by ants. We found that ants dispersed seeds farther in habitat patches connected by corridors, but only in patch centers. We did not see an effect on the total number of seeds moved or the rate ants detected seeds. Furthermore, we did not see any differences in ant community composition across patch types, suggesting that shifts in ant behavior or other factors increased ant seed dispersal in patches connected by corridors. Long-distance seed dispersal by ants that requires an accumulation of short-distance dispersal events over generations may be an underappreciated mechanism through which corridors increase plant diversity.
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    Appeal of the Apple: Exploring consumer perceptions of hard cider in the Northeast and Mid-Atlantic United States
    Calvert, Martha D.; Neill, Clinton L.; Stewart, Amanda C.; Chang, Elizabeth A. B.; Whitehead, Susan R.; Lahne, Jacob (Taylor & Francis, 2023-10-23)
    Alcoholic or “hard” cider is experiencing a resurgence in popularity, particularly throughout the Northeast and Mid-Atlantic regions of the United States. Yet, many stakeholders struggle to understand how consumers define and distinguish hard cider from the sea of options in the saturated alcoholic beverage market. This study aimed to explore consumer preferences for hard cider using a phenomenological, qualitative approach. The research comprised 14 focus groups with regular cider consumers (99 participants) throughout three leading cider-producing states in the Northeast and Mid-Atlantic United States: Virginia, Vermont, and New York. All focus group sessions were subject to reflexive thematic analysis for themes broadly related to cider product preference and the cider-drinking experience. Results of the study suggest that cider preference is motivated largely by sensory quality in addition to various other factors including perceived health effects, regionality and proximity, the drinking occasion, and product information. Results also emphasize the importance of nostalgia in cider sensory experiences, as well as the role of social norms in consumer valuation of cider products. Overall, this research highlights diverse consumer preferences for cider and serves as a framework for using qualitative research methods to explore consumer preferences in the food and beverage industries.
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    Appeal of the Apple: Investigating Preference, Perception, and Communication Around Hard Cider in the Northeast and Mid-Atlantic United States
    Calvert, Martha D. (Virginia Tech, 2023-07-03)
    Alcoholic or "hard" cider, as it is known in the United States, is experiencing a resurgence in popularity worldwide, but most relevantly throughout the Northeast and Mid-Atlantic regions of the United States. Cider has a rich history of being America's drink of choice, beginning with the native apple trees of indigenous communities and the proliferation of apple growing in the original American colonies. Today, cider is becoming popular particularly in the Northeast and Mid-Atlantic where New York, Virginia, and Vermont are the 1st, 8th, 12th ranked states with the most cideries in America. In light of the American cider industry experiencing such a renaissance, leading industry stakeholders and various other scholars have drawn attention to the need for increased clarity regarding consumer and producer perceptions of cider quality, as well as a more comprehensive understanding of cider sensory quality. This dissertation utilizes qualitative research methods, including focus groups and interviews conducted in New York, Virginia, and Vermont, to explore consumer and producer preferences of cider and the cider-drinking experience. In addition, this research employed traditional sensory descriptive analysis (DA) to quantify sensory differences across cider products. Lastly, this research presents findings on the use of biterm topic modeling (BTM), an emergent method of text mining for small datasets, to explore topics of discussion in cider marketing materials for products in the American cider marketplace. This dissertation presents evidence of preferences, sensory perception, and discourse within a snapshot of the current American cider industry. Cider consumers and producers prioritize flavor when discussing cider quality, but also value how cider is made and where it comes from. Consumers, in particular, are nostalgic about the cider-drinking community and culture that is omnipresent in the Northeast. Secondly, the sensory quality of ciders can be discriminated across multiple variables, including region of origin, packaging, and style; suggesting that the sensory space of American cider products is diverse and nuanced. Lastly, when marketing cider products through website platforms, cider producers tend to emphasize topics related to sensory attributes, production elements, food-pairing, flavorings, and apple varieties. With a greater understanding of consumer and producer preferences of cider, cider sensory quality, and cider communication, industry actors and stakeholders may have a more actionable understanding of where the cider industry may be headed with continued growth. As well, this dissertation provides a framework for the use of qualitative and text mining tools to better understand facets of consumption and production, as well as marketing language in the food and beverage space.
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    Assembly and dynamics of the apple carposphere microbiome during fruit development and storage
    Zhimo, V. Yeka; Kumar, Ajay; Biasi, Antonio; Abdelfattah, Ahmed; Sharma, Vijay Kumar; Salim, Shoshana; Feygenberg, Oleg; Bartuv, Rotem; Freilich, Shiri; Whitehead, Susan R.; Wisniewski, Michael; Droby, Samir (Frontiers, 2022-08-09)
    Microbial communities associated with fruit can contribute to quality and pathogen resistance, but little is known about their assembly and dynamics during fruit development and storage. Three apple cultivars growing under the same environmental conditions were utilized to examine the apple carposphere microbiome composition and structure at different developmental stages and storage. There was a significant effect (Adonis, p <= 0.001) of fruit genotype and its developmental stages and storage times on the fruit surface microbial assemblage and a strong temporal microbial community succession was detected (Mantel test: R <= 0.5, p = 0.001) in both bacterial and fungal communities. A set of 15 bacterial and 35 fungal core successional taxa and members exhibiting differential abundances at different fruit stages were identified. For the first time, we show the existence of underlying universal dynamics in the assembly of fruit-associated microbiomes. We also provide evidence of strong microbial cross-domain associations and uncover potential microbe-microbe correlations in the apple carposphere. Together our findings shed light on how the fruit carposphere assemble and change over time, and provide new insights into fruit microbial ecology.
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    Biochar amendment as a tool for improving soil health and carbon sequestration in agro-ecosystems
    Drew, Sophia Eliza (Virginia Tech, 2022-09-14)
    Conventional farming practices and land-use conversions drive carbon out of soil and into the atmosphere, where it contributes to climate change. Biochar, a soil amendment produced by pyrolyzing organic feedstocks under low-oxygen conditions, is a promising tool to restore soil carbon and draw down atmospheric carbon dioxide. Biochar has received considerable attention from scientists, growers, and environmentalists in the last 20 years, but there is still a gap between academic research and practical recommendations on biochar production and application that are relevant to small-scale growers. Here I present the results from two complementary studies that demonstrate the utility of local-scale biochar systems and provide some recommendations for those looking to work with biochar. The first study sought to determine the impact of biochar amendments on soil carbon and nutrient retention on three working farms across a variety of soil types, cropping systems, and climates in the United States. The effect of biochar amendment depended on initial soil characteristics and the properties of the biochar applied. Biochar amendments increased soil carbon in all three sites and increased soil nitrogen at two of the three. In this study pyrolysis conditions appeared to be as important as local soils and climate influences on the efficacy of biochar treatments. The second study was a life cycle assessment using SimaPro software to quantify the carbon balance and global warming potential of biochar produced from three local feedstocks (softwood, hardwood, and hay) applied to pasture soils in Southwest Virginia. Feedstock type, pyrolysis gas yield, and transportation distance significantly contributed to variation in the carbon balance of each agro-ecosystem. Biochar made from softwood lumber scraps performed best, with the highest net carbon storage and lowest global warming potential, followed by biochar made from hardwood scraps. Hay biochar performed worst, with positive carbon emissions (i.e., more carbon released than stored over its life cycle) in most scenarios tested, mainly because of its low biochar yield and the carbon emissions associated with agronomic production and transportation. Together these studies demonstrate the potential of local biochar systems to improve both soil health and carbon sequestration, and reinforce how important it is to know the characteristics of the soil and the production history and properties of the biochar being applied in order to meet soil health and carbon sequestration goals.
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    Biotic and abiotic mechanisms shaping multi-species interactions
    Maynard, Lauren Danielle (Virginia Tech, 2022-12-20)
    Interactions are important drivers of selection and community structure, which makes the study of multi-species interactions critical for understanding the ecology and evolution of organisms. This dissertation includes four data chapters that examine the biotic and abiotic mechanisms that shape multi-species interactions in both tropical and temperate ecosystems. The first three data chapters (Chapters 2–4) were completed within a Neotropical rainforest in Costa Rica and focus on one plant genus, Piper (Piperaceae). The final data chapter (Chapter 5) was conducted within a working landscape of soybean (Glycine max) fields in eastern Maryland, USA. In Chapter 2, I explore intra- and inter-specific dietary niche partitioning of Piper fruits among three frugivorous bats, illustrating the importance of fine-scale mechanisms that facilitate species coexistence and influence plant–animal interactions. In Chapter 3, I demonstrate how the chemical ecology of a Neotropical shrub, Piper sancti-felicis, shapes fruit interactions with antagonists (fruit fungi) and mutualists (frugivorous bats and birds), developing a foundation for understanding evolutionary ecology of plant chemical traits based on phytochemical investment patterns. In Chapter 4, I describe the direct and indirect impacts of elevated temperature and CO2 concentration on the plant traits and interactions in Piper generalense, improving our understanding of the effects of climate change on a Neotropical plant–herbivore system. In Chapter 5, I explore the biotic (herbivore-induced plant volatiles) and abiotic (fine-scale weather conditions) drivers affecting insectivorous bat foraging in soybean fields in eastern Maryland, providing a pathway to further investigate new strategies for integrated pest management. As a collective work, this dissertation disentangles the nuances of multi-species interactions, exploring foundational mechanisms underlying biodiversity maintenance as well as answering applied questions to address a changing climate and aid sustainable agriculture.
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    A communal catalogue reveals Earth's multiscale microbial diversity
    Thompson, Luke R.; Sanders, Jon G.; McDonald, Daniel; Amir, Amnon; Ladau, Joshua; Locey, Kenneth J.; Prill, Robert J.; Tripathi, Anupriya; Gibbons, Sean M.; Ackermann, Gail; Navas-Molina, Jose A.; Janssen, Stefan; Kopylova, Evguenia; Vazquez-Baeza, Yoshiki; Gonzalez, Antonio; Morton, James T.; Mirarab, Siavash; Xu, Zhenjiang Zech; Jiang, Lingjing; Haroon, Mohamed F.; Kanbar, Jad; Zhu, Qiyun; Song, Se Jin; Kosciolek, Tomasz; Bokulich, Nicholas A.; Lefler, Joshua; Brislawn, Colin J.; Humphrey, Gregory; Owens, Sarah M.; Hampton-Marcell, Jarrad; Berg-Lyons, Donna; McKenzie, Valerie; Fierer, Noah; Fuhrman, Jed A.; Clauset, Aaron; Stevens, Rick L.; Shade, Ashley; Pollard, Katherine S.; Goodwin, Kelly D.; Jansson, Janet K.; Gilbert, Jack A.; Knight, Rob; Rivera, Jose L. Agosto; Al-Moosawi, Lisa; Alverdy, John; Amato, Katherine R.; Andras, Jason; Angenent, Largus T.; Antonopoulos, Dionysios A.; Apprill, Amy; Armitage, David; Ballantine, Kate; Barta, Jiri; Baum, Julia K.; Berry, Allison; Bhatnagar, Ashish; Bhatnagar, Monica; Biddle, Jennifer F.; Bittner, Lucie; Boldgiv, Bazartseren; Bottos, Eric M.; Boyer, Donal M.; Braun, Josephine; Brazelton, William; Brearley, Francis Q.; Campbell, Alexandra H.; Caporaso, J. Gregory; Cardona, Cesar; Carroll, JoLynn; Cary, S. Craig; Casper, Brenda B.; Charles, Trevor C.; Chu, Haiyan; Claar, Danielle C.; Clark, Robert G.; Clayton, Jonathan B.; Clemente, Jose C.; Cochran, Alyssa; Coleman, Maureen L.; Collins, Gavin; Colwell, Rita R.; Contreras, Monica; Crary, Benjamin B.; Creer, Simon; Cristol, Daniel A.; Crump, Byron C.; Cui, Duoying; Daly, Sarah E.; Davalos, Liliana; Dawson, Russell D.; Defazio, Jennifer; Delsuc, Frederic; Dionisi, Hebe M.; Dominguez-Bello, Maria Gloria; Dowell, Robin; Dubinsky, Eric A.; Dunn, Peter O.; Ercolini, Danilo; Espinoza, Robert E.; Ezenwa, Vanessa; Fenner, Nathalie; Findlay, Helen S.; Fleming, Irma D.; Fogliano, Vincenzo; Forsman, Anna; Freeman, Chris; Friedman, Elliot S.; Galindo, Giancarlo; Garcia, Liza; Alexandra Garcia-Amado, Maria; Garshelis, David; Gasser, Robin B.; Gerdts, Gunnar; Gibson, Molly K.; Gifford, Isaac; Gill, Ryan T.; Giray, Tugrul; Gittel, Antje; Golyshin, Peter; Gong, Donglai; Grossart, Hans-Peter; Guyton, Kristina; Haig, Sarah-Jane; Hale, Vanessa; Hall, Ross Stephen; Hallam, Steven J.; Handley, Kim M.; Hasan, Nur A.; Haydon, Shane R.; Hickman, Jonathan E.; Hidalgo, Glida; Hofmockel, Kirsten S.; Hooker, Jeff; Hulth, Stefan; Hultman, Jenni; Hyde, Embriette; Ibanez-Alamo, Juan Diego; Jastrow, Julie D.; Jex, Aaron R.; Johnson, L. Scott; Johnston, Eric R.; Joseph, Stephen; Jurburg, Stephanie D.; Jurelevicius, Diogo; Karlsson, Anders; Karlsson, Roger; Kauppinen, Seth; Kellogg, Colleen T. E.; Kennedy, Suzanne J.; Kerkhof, Lee J.; King, Gary M.; Kling, George W.; Koehler, Anson V.; Krezalek, Monika; Kueneman, Jordan G.; Lamendella, Regina; Landon, Emily M.; Lane-deGraaf, Kelly; LaRoche, Julie; Larsen, Peter; Laverock, Bonnie; Lax, Simon; Lentino, Miguel; Levin, Iris I.; Liancourt, Pierre; Liang, Wenju; Linz, Alexandra M.; Lipson, David A.; Liu, Yongqin; Lladser, Manuel E.; Lozada, Mariana; Spirito, Catherine M.; MacCormack, Walter P.; MacRae-Crerar, Aurora; Magris, Magda; Martin-Platero, Antonio M.; Martin-Vivaldi, Manuel; Margarita Martinez, L.; Martinez-Bueno, Manuel; Marzinelli, Ezequiel M.; Mason, Olivia U.; Mayer, Gregory D.; McDevitt-Irwin, Jamie M.; McDonald, James E.; McGuire, Krista L.; McMahon, Katherine D.; McMinds, Ryan; Medina, Monica; Mendelson, Joseph R., III; Metcalf, Jessica L.; Meyer, Folker; Michelangeli, Fabian; Miller, Kim; Mills, David A.; Minich, Jeremiah; Mocali, Stefano; Moitinho-Silva, Lucas; Moore, Anni; Morgan-Kiss, Rachael M.; Munroe, Paul; Myrold, David; Neufeld, Josh D.; Ni, Yingying; Nicol, Graeme W.; Nielsen, Shaun; Nissimov, Jozef I.; Niu, Kefeng; Nolan, Matthew J.; Noyce, Karen; O'Brien, Sarah L.; Okamoto, Noriko; Orlando, Ludovic; Castellano, Yadira Ortiz; Osuolale, Olayinka; Oswald, Wyatt; Parnell, Jacob; Peralta-Sanchez, Juan M.; Petraitis, Peter; Pfister, Catherine; Pilon-Smits, Elizabeth; Piombino, Paola; Pointing, Stephen B.; Pollock, F. Joseph; Potter, Caitlin; Prithiviraj, Bharath; Quince, Christopher; Rani, Asha; Ranjan, Ravi; Rao, Subramanya; Rees, Andrew P.; Richardson, Miles; Riebesell, Ulf; Robinson, Carol; Rockne, Karl J.; Rodriguezl, Selena Marie; Rohwer, Forest; Roundstone, Wayne; Safran, Rebecca J.; Sangwan, Naseer; Sanz, Virginia; Schrenk, Matthew; Schrenzel, Mark D.; Scott, Nicole M.; Seger, Rita L.; Seguin-Orlando, Andaine; Seldin, Lucy; Seyler, Lauren M.; Shakhsheer, Baddr; Sheets, Gabriela M.; Shen, Congcong; Shi, Yu; Shin, Hakdong; Shogan, Benjamin D.; Shutler, Dave; Siegel, Jeffrey; Simmons, Steve; Sjoling, Sara; Smith, Daniel P.; Soler, Juan J.; Sperling, Martin; Steinberg, Peter D.; Stephens, Brent; Stevens, Melita A.; Taghavi, Safiyh; Tai, Vera; Tait, Karen; Tan, Chia L.; Tas, Neslihan; Taylor, D. Lee; Thomas, Torsten; Timling, Ina; Turner, Benjamin L.; Urich, Tim; Ursell, Luke K.; van der Lelie, Daniel; Van Treuren, William; van Zwieten, Lukas; Vargas-Robles, Daniela; Thurber, Rebecca Vega; Vitaglione, Paola; Walker, Donald A.; Walters, William A.; Wang, Shi; Wang, Tao; Weaver, Tom; Webster, Nicole S.; Wehrle, Beck; Weisenhorn, Pamela; Weiss, Sophie; Werner, Jeffrey J.; West, Kristin; Whitehead, Andrew; Whitehead, Susan R.; Whittingham, Linda A.; Willerslev, Eske; Williams, Allison E.; Wood, Stephen A.; Woodhams, Douglas C.; Yang, Yeqin; Zaneveld, Jesse; Zarraonaindia, Iratxe; Zhang, Qikun; Zhao, Hongxia (2017-11-23)
    Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.
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    Comparative Metabolomics of Fruits and Leaves in a Hyperdiverse Lineage Suggests Fruits Are a Key Incubator of Phytochemical Diversification
    Schneider, Gerald F.; Salazar, Diego; Hildreth, Sherry B.; Helm, Richard F.; Whitehead, Susan R. (Frontiers, 2021-08-30)
    Interactions between plants and leaf herbivores have long been implicated as the major driver of plant secondary metabolite diversity. However, other plant-animal interactions, such as those between fruits and frugivores, may also be involved in phytochemical diversification. Using 12 species of Piper, we conducted untargeted metabolomics and molecular networking with extracts of fruits and leaves. We evaluated organ-specific secondary metabolite composition and compared multiple dimensions of phytochemical diversity across organs, including richness, structural complexity, and variability across samples at multiple scales within and across species. Plant organ identity, species identity, and the interaction between the two all significantly influenced secondary metabolite composition. Leaves and fruit shared a majority of compounds, but fruits contained more unique compounds and had higher total estimated chemical richness. While the relative levels of chemical richness and structural complexity across organs varied substantially across species, fruit diversity exceeded leaf diversity in more species than the reverse. Furthermore, the variance in chemical composition across samples was higher for fruits than leaves. By documenting a broad pattern of high phytochemical diversity in fruits relative to leaves, this study lays groundwork for incorporating fruit into a comprehensive and integrative understanding of the ecological and evolutionary factors shaping secondary metabolite composition at the whole-plant level.
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    Dietary resource overlap among three species of frugivorous bat in Costa Rica
    Maynard, Lauren D.; Ananda, Ariana; Sides, Maria F.; Burk, Hannah; Whitehead, Susan R. (Cambridge University Press, 2019-03-21)
    The maintenance of biodiversity in tropical forests is thought to be dependent on fine-scale mechanisms of niche partitioning that allow species to coexist. This study examined whether three species of short-tailed fruit bat that co-occur at a lowland tropical forest site in Costa Rica (Carollia castanea, C. perspicillata, C. sowelli) avoid inter- and intraspecific competition through dietary specialization on species in the genus Piper. First, dietary composition was examined using faecal samples (N = 210), which yielded three main findings: (1) bat species and sexes vary in overall reliance on fruits of Piper, with a higher percentage of seeds of Piper detected in the diets of C. castanea (98.2%) and females (91.5%); (2) adults and juveniles partition species of Piper by habitat, with a lower percentage of mid- to late-successional species of Piper detected in adults (20.8%); and (3) overall, there is a strong dietary overlap among and within the three species of Carollia. Second, controlled choice experiments were conducted with individual bats (N = 123) to examine preferences for different species of Piper. These results indicated few differences in Piper preference based on bat species, sex, age class or reproductive status, suggesting preference is not the primary mechanism shaping the observed differences in dietary composition. Overall, the dietary composition and preference similarities suggest there is strong competition both among and within the three species of Carollia for food resources.
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    Diversity and function of terpene synthases in the production of carrot aroma and flavor compounds
    Muchlinski, Andrew; Ibdah, Mwafaq; Ellison, Shelby; Yahyaa, Mossab; Nawade, Bhagwat; Laliberte, Suzanne; Senalik, Douglas; Simon, Philipp; Whitehead, Susan R.; Tholl, Dorothea (2020-06-19)
    Carrot (Daucus carota L.) is an important root vegetable crop with high nutritional value, characteristic flavor, and benefits to human health. D. carota tissues produce an essential oil that is rich in volatile terpenes and plays a major role in carrot aroma and flavor. Although terpene composition represents a critical quality attribute of carrots, little is known about the biosynthesis of terpenes in this crop. Here, we functionally characterized 19 terpene synthase (TPS) genes in an orange carrot (genotype DH1) and compared tissue-specific expression profiles and in vitro products of their recombinant proteins with volatile terpene profiles from DH1 and four other colored carrot genotypes. In addition to the previously reported (E)-beta -caryophyllene synthase (DcTPS01), we biochemically characterized several TPS proteins with direct correlations to major compounds of carrot flavor and aroma including germacrene D (DcTPS7/11), gamma -terpinene (DcTPS30) and alpha -terpinolene (DcTPS03). Random forest analysis of volatiles from colored carrot cultivars identified nine terpenes that were clearly distinct among the cultivars and likely contribute to differences in sensory quality. Correlation of TPS gene expression and terpene metabolite profiles supported the function of DcTPS01 and DcTPS03 in these cultivars. Our findings provide a roadmap for future breeding efforts to enhance carrot flavor and aroma.
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    Effect of Washing, Waxing and Low-Temperature Storage on the Postharvest Microbiome of Apple
    Abdelfattah, Ahmed; Whitehead, Susan R.; Macarisin, Dumitru; Liu, Jia; Burchard, Erik; Freilich, Shiri; Dardick, Christopher; Droby, Samir; Wisniewski, Michael (MDPI, 2020-06-23)
    There is growing recognition of the role that the microbiome plays in the health and physiology of many plant species. However, considerably less research has been conducted on the postharvest microbiome of produce and the impact that postharvest processing may have on its composition. Here, amplicon sequencing was used to study the effect of washing, waxing, and low-temperature storage at 2 °C for six months on the bacterial and fungal communities of apple calyx-end, stem-end, and peel tissues. The results of the present work reveal that tissue-type is the main factor defining fungal and bacterial diversity and community composition on apple fruit. Both postharvest treatments and low temperature storage had a strong impact on the fungal and bacterial diversity and community composition of these tissue types. Distinct spatial and temporal changes in the composition and diversity of the microbiota were observed in response to various postharvest management practices. The greatest impact was attributed to sanitation practices with major differences among unwashed, washed and washed-waxed apples. The magnitude of the differences, however, was tissue-specific, with the greatest impact occurring on peel tissues. Temporally, the largest shift occurred during the first two months of low-temperature storage, although fungi were more affected by storage time than bacteria. In general, fungi and bacteria were impacted equally by sanitation practices, especially the epiphytic microflora of peel tissues. This research provides a foundation for understanding the impact of postharvest management practices on the microbiome of apple and its potential subsequent effects on postharvest disease management and food safety.
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    Effects of seed morphology and elaiosome chemical composition on attractiveness of five Trillium species to seed-dispersing ants
    Miller, Chelsea N.; Whitehead, Susan R.; Kwit, Charles (2020-03)
    Morphological and chemical attributes of diaspores in myrmecochorous plants have been shown to affect seed dispersal by ants, but the relative importance of these attributes in determining seed attractiveness and dispersal success is poorly understood. We explored whether differences in diaspore morphology, elaiosome fatty acids, or elaiosome phytochemical profiles explain the differential attractiveness of five species in the genus Trillium to eastern North American forest ants. Species were ranked from least to most attractive based on empirically-derived seed dispersal probabilities in our study system, and we compared diaspore traits to test our hypotheses that more attractive species will have larger diaspores, greater concentrations of elaiosome fatty acids, and distinct elaiosome phytochemistry compared to the less attractive species. Diaspore length, width, mass, and elaiosome length were significantly greater in the more attractive species. Using gas chromatography-mass spectrometry, we found significantly higher concentrations of oleic, linoleic, hexadecenoic, stearic, palmitoleic, and total fatty acids in elaiosomes of the more attractive species. Multivariate assessments revealed that elaiosome phytochemical profiles, identified through liquid chromatography-mass spectrometry, were more homogeneous for the more attractive species. Random forest classification models (RFCM) identified several elaiosome phytochemicals that differed significantly among species. Random forest regression models revealed that some of the compounds identified by RFCM, including methylhistidine (alpha-amino acid) and d-glucarate (carbohydrate), were positively related to seed dispersal probabilities, while others, including salicylate (salicylic acid) and citrulline (L-alpha-amino acid), were negatively related. These results supported our hypotheses that the more attractive species of Trillium-which are geographically widespread compared to their less attractive, endemic congeners-are characterized by larger diaspores, greater concentrations of fatty acids, and distinct elaiosome phytochemistry. Further advances in our understanding of seed dispersal effectiveness in myrmecochorous systems will benefit from a portrayal of dispersal unit chemical and physical traits, and their combined responses to selection pressures.
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    Exploring cider website descriptions using a novel text mining approach
    Calvert, Martha D.; Cole, Elizabeth; Neill, Clinton L.; Stewart, Amanda C.; Whitehead, Susan R.; Lahne, Jacob (Wiley, 2023-05)
    Rapid methods of text analysis are increasingly important tools for efficiently extracting and understanding communication within the food and beverage space. This study aimed to use frequency-based text mining and biterm topic modeling (BTM) as tools for analyzing how cider products are communicated and marketed on cider-producer websites for products made in Virginia, Vermont, and New York. BTM has been previously used to explore topics in small corpora of text data, and frequency-based text mining is efficient for exploring patterns of text across different documents or filters. The present dataset comprised 1115 cider products and their website descriptions extracted from 124 total cider-producer websites during 2020 and 2021. Results of the text mining analyses suggest that cider website descriptions emphasize food-pairing, production, and sensory quality information. Altogether, this research presents the text mining approaches for exploring food and beverage communication. Practical applicationsThis research will be valuable to stakeholders in the United States' cider industry by providing relevant insight as to how cider marketing and sensory communication varies based on extrinsic product factors, such as geography and packaging. This research also demonstrates the efficiency and potential of text mining tools for exploring language and communication related to foods, beverages, and sensory quality. Further, this research provides a framework for extracting sensory-specific language from a large corpus of data, which may be adopted by other researchers wishing to apply rapid descriptive methods in the sensory, quality, and consumer research fields.
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    Fruit secondary metabolites alter the quantity and quality of a seed dispersal mutualism
    Nelson, Annika S.; Gelambi, Mariana; Morales-M., Estefania; Whitehead, Susan R. (Wiley, 2023-05)
    Plant secondary metabolites are key mechanistic drivers of species interactions. These metabolites have primarily been studied for their role in defense, but they can also have important consequences for mutualisms, including seed dispersal. Although the primary function of fleshy fruits is to attract seed-dispersing animals, fruits often contain complex mixtures of toxic or deterrent secondary metabolites that can reduce the quantity or quality of seed dispersal mutualisms. Furthermore, because seeds are often dispersed across multiple stages by several dispersers, the net consequences of fruit secondary metabolites for the effectiveness of seed dispersal and ultimately plant fitness are poorly understood. Here, we tested the effects of amides, nitrogen-based defensive compounds common in fruits of the neotropical plant genus Piper (Piperaceae), on seed dispersal effectiveness (SDE) by ants, which are common secondary seed dispersers. We experimentally added amide extracts to Piper fruits both in the field and lab, finding that amides reduced the quantity of secondary seed dispersal by reducing ant recruitment (87%) and fruit removal rates (58% and 66% in the field and lab, respectively). Moreover, amides not only reduced dispersal quantity but also altered seed dispersal quality by shifting the community composition of recruiting ants (notably by reducing the recruitment of the most effective disperser by 90% but having no detectable effect on the recruitment of a cheater species that removes fruit pulp without dispersing seeds). Although amides did not affect the distance ants initially carried seeds, they altered the quality of seed dispersal by reducing the likelihood of ants cleaning seeds (67%) and increasing their likelihood of ants redispersing seeds outside of the nest (200%). Overall, these results demonstrate that secondary metabolites can alter the effectiveness of plant mutualisms, by both reducing mutualism quantity and altering mutualism quality through multiple mechanisms. These findings present a critical step in understanding the factors mediating the outcomes of seed dispersal and, more broadly, demonstrate the importance of considering how defensive secondary metabolites influence the outcomes of mutualisms surrounding plants.
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    Fruits, frugivores, and the evolution of phytochemical diversity
    Whitehead, Susan R.; Schneider, Gerald F.; Dybzinski, Ray; Nelson, Annika S.; Gelambi, Mariana; Jos, Elsa; Beckman, Noelle G. (2021-06-14)
    Plants produce an enormous diversity of secondary metabolites, but the evolutionary mechanisms that maintain this diversity are still unclear. The interaction diversity hypothesis suggests that complex chemical phenotypes are maintained because different metabolites benefit plants in different pairwise interactions with a diversity of other organisms. In this synthesis, we extend the interaction diversity hypothesis to consider that fruits, as potential hotspots of interactions with both antagonists and mutualists, are likely important incubators of phytochemical diversity. We provide a case study focused on the Neotropical shrub Piper reticulatum that demonstrates: 1) secondary metabolites in fruits have complex and cascading effects for shaping the outcome of both mutualistic and antagonistic fruit-frugivore interactions, and; 2) fruits can harbor substantially higher levels of phytochemical diversity than leaves, even though leaves have been the primary focus of plant chemical ecology research for decades. We then suggest a number of research priorities for integrating chemical ecology with fruit-frugivore interaction research and make specific, testable predictions for patterns that should emerge if fruit interaction diversity has helped shape phytochemical diversity. Testing these predictions in a range of systems will provide new insight into the mechanisms driving frugivory and seed dispersal and shape an improved, whole-plant perspective on plant chemical trait evolution.
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    Induced defenses in apple fruits: linking fruit chemistry, quality, and plant-insect-microbe interactions
    Meakem, Victoria (Virginia Tech, 2020-06-24)
    Plants synthesize a diverse array of phytochemicals in response to interactions with herbivores, pathogens, and commensal microbes. These phytochemicals may simultaneously enhance crop defense and quality, representing a potential pest management strategy. However, plant chemical responses to different types and levels of biotic interactions remain unclear, particularly in fruit tissues, and the feasibility of inducing these defenses through elicitor application in field environments also requires further examination. Thus, apples were used to 1) examine the impact of distinct communities of biotic interactions among plants, insects, and microbes on fruit phenolic chemistry, and 2) examine the impact of the phytohormones jasmonic acid (JA), salicylic acid (SA), and melatonin (M) on fruit phenolic chemistry and resistance against pests and pathogens. Ultimately, phenolic defenses were induced by fungal damage primarily in ripe pulp tissues, where there was also a positive relationship between fungal endophyte and phenolic diversity, supporting a broad hypothesis that chemical diversity may increase with biotic diversity. Additionally, two compounds were upregulated in response to fungal damage: chlorogenic acid and an unidentified benzoic acid. Elicitor applications did not affect phenolic chemistry, but the combined application of JA-SA analogues had some chemical or physical effect, as this treatment reduced emergence of the insect Rhagoletis pomonella. Thus, fruit induced defenses may be tissue-specific and subject to temporal, environmental, or genotypic variation. Overall, these chapters examined the relationship between biotic interactions and induced fruit chemistry, with the goal of improving understanding of plant-microbe-insect interactions and incorporating these interactions into more sustainable agricultural practices.
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    Insect pest management in hemp in Virginia
    Britt, Kadie Elizabeth (Virginia Tech, 2021-04-13)
    For the first time in many decades, a hemp pilot program was initiated in Virginia in 2016. Outdoor surveys were conducted in the 2017 and 2018 field seasons to record insect presence and feeding injury to plants. Multiple insect pests were present, including corn earworm (Helicoverpa zea [Boddie]) (Lepidoptera: Noctuidae), brown marmorated stink bug (Halyomorpha halys [Stål]) (Hemiptera: Pentatomidae), and cannabis aphid (Phorodon cannabis) (Hemiptera: Aphididae). In 2019, indoor production surveys revealed that cannabis aphid, twospotted spider mite (Tetranychus urticae Koch) (Acari: Tetranychidae), and hemp russet mite (Aculops cannabicola [Farkas]) (Acari: Eriophyidae) would likely cause production issues. Very little is known about the impact of insect defoliation in hemp so studies were conducted in 2018-2020 to determine impacts on yield and cannabinoid content of grain and cannabinoid variety hemp due to leaf surface area loss. In Virginia over two growing seasons, manual removal of leaf tissue in grain and CBD cultivars did not significantly impact observable effects on physical yield (seed or bud weight) or cannabinoid content (CBD or THC) at time of harvest. Corn earworm is the major pest of hemp produced outdoors and studies occurred to evaluate monitoring and management strategies. Pheromone traps may be valuable in determining when corn earworm moths are present in the vicinity of hemp fields but are not useful in predicting larval presence in buds or final crop damage. Larval presence and final crop damage are related. Brown marmorated stink bug does not appear to be a concern in hemp, at least at this time.
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    Physalis angulata pollination after herbivory: the effects of herbivore damage on pollinator preference
    Xu, Freddie M.; Whitehead, Susan R. (Virginia Tech, 2018-07-26)
    Pollination is the pinnacle of a plant’s life cycle. Progeny carry on paternal traits for higher fitness and survival while also maintaining genetic diversity among populations. While some species such as Physalis angulata can undergo self-pollination (“selfing”), outcrossing with other plants via pollinators still yields higher quality and number of seeds. Thus, the selection/avoidance of pollinators for certain plants is crucial in determining the health of future generations. This study examines pollinator preferences for plant flowers following herbivory. We created two groups of P. angulata, exposing one to Manduca sexta (a specialist herbivore for the Solanaceae family) and keeping the other as a control. Following substantial damage, the plants were introduced to the generalist pollinator Bombus impatiens, and interaction data were recorded for both groups. Analysis indicates a significant effect of herbivory on time elapsed until plants were first visited by pollinators. However, no impact of herbivory was seen on flower production or on pollinator preference regarding number of flowers visited, number of unique bumblebee visitors, and average visit duration per flower. We therefore conclude that herbivory by M. sexta on P. angulata does generate a significant effect on pollination as mediated by B. impatiens due to the increased time needed by pollinators to locate plants and flowers following herbivore damage. Expanding upon previously observed ecological relationships between herbivory and plant reproductive success, the novel mechanism of time to first visitation has potential applications for agricultural outputs as protection against pests could yield higher pollination rates during finite growing seasons.
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    Poison ivy hairy root cultures enable a stable transformation system suitable for detailed investigation of urushiol metabolism
    Lott, Aneirin A.; Freed, Catherine P.; Dickinson, Christopher C.; Whitehead, Susan R.; Collakova, Eva; Jelesko, John G. (Wiley, 2020)
    Poison ivy (Toxicodendron radicans) is best known for causing exasperating allergenic delayed-contact dermatitis symptoms that last for weeks on persons who have contacted the plant. Urushiols are alkylcatechols produced by poison ivy responsible for causing this dermatitis. While urushiol chemical structures are well known, the metabolic intermediates and genes responsible for their biosynthesis have not been experimentally validated. A molecular genetic characterization of urushiol biosynthesis in poison ivy will require stable genetic transformation and subsequent regeneration of organs that retain the capacity synthesize urushiol. To this end, Agrobacterium rhizogenes was used to generate hormone-independent poison ivy hairy root cultures. Optimal conditions for hairy root formation were skotomorphic poison ivy hypocotyls prick-inoculated with A. rhizogenes, and preferential propagation of cultures with an atypical clumpy hairy root growth habit. The origin of the poison ivy accession used for A. rhizogenes prick-inoculation did not affect the initial formation of calli/ hairy root primordia, but rather significantly influenced the establishment of longterm hormone-independent hairy root growth. A. rhizogenes harboring a recombinant T-DNA binary plasmid with an intron-containing Firefly Luciferase gene produced stable transgenic hairy root lines expressing luciferase activity at high frequency. Poison ivy hairy root lines produced significantly lower steady-state urushiol levels relative to wild-type roots, but higher urushiol levels than a poison ivy undifferentiated callus line with undetectable urushiol levels, suggesting that urushiol biosynthesis requires intact poison ivy organs. The lower urushiol levels in poison ivy hairy root lines facilitated the first identification of anacardic acid metabolites initially in hairy roots, and subsequently in wild-type roots as well. This study establishes a transformation hairy root regeneration protocol for poison ivy that can serve as a platform for future reverse-genetic studies of urushiol biosynthesis in poison ivy hairy roots.