Publications

Most recent publications:

Whitehill JGA, Popova-Butler S, Green-Church KB, Koch JL, Herms DA, Bonello P (2011) Interspecific proteomic comparisons reveal ash phloem genes potentially involved in constitutive resistance to the emerald ash borer. PLoS ONE 6: e24863

Associated People:
Enrico Bonello

Associated Projects:
Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Abstract:
The emerald ash borer (Agrilus planipennis) is an invasive wood-boring beetle that has killed millions of ash trees since its accidental introduction to North America.  All North American ash species (Fraxinus spp.) that emerald ash borer has encountered so far are susceptible, while an Asian species, Manchurian ash (F. mandshurica), which shares an evolutionary history with emerald ash borer, is resistant.  Phylogenetic evidence places North American black ash (F. nigra) and Manchurian ash in the same clade and section, yet black ash is highly susceptible to the emerald ash borer.  This contrast provides an opportunity to compare the genetic traits of the two species and identify those with a potential role in defense/resistance. 


Muilenburg V, Phelan P, Bonello P, Herms D (2011) Inter- and intra-specific variation in stem phloem phenolics of paper birch (Betula papyrifera) and European white birch (Betula pendula). Journal of Chemical Ecology 37: 1193-1202

Associated People:
Enrico Bonello

Abstract:
Outbreaks of bronze birch borer (BBB) ( Agrilus anxius ), a wood-boring beetle endemic to North America, have been associated with widespread mortality of birch ( Betula spp.). There is substantial inter- and intra-specific variation in birch resistance to BBB. Species endemic to North America, such as paper birch ( B. papyrifera ), have coevolved with BBB and are more resistant than European and Asian birch species, such as European white birch ( B. pendula ), which lack an evolutionary history with BBB. Borer larvae feed on stem phloem tissue. Therefore, in search of potential resistance mechanisms against BBB, we compared the constitutive phenolic profile of stem phloem tissue of paper birch with that of European white birch. We also analyzed intraspecific variation in phenolic composition among clones and/or half-siblings of both species. Three phenolics (coumaroylquinic acid, betuloside pentoside A, and a diarylheptanoid hexoside) were detected only in paper birch, and concentrations of six other phenolics were significantly higher in paper birch. These differences may contribute to the high resistance of paper birch to BBB relative to European white birch. There was significant intraspecific variation in four of 17 phenolics found in paper birch and in five of 14 found in European white birch, but clones and half-siblings within each species could not be distinguished by phenolic composition using multivariate analysis.


Kleczewski N, Herms DA, Bonello P (2012) Nutrient and water availability alter belowground patterns of biomass allocation, carbon partitioning, and ectomycorrhizal abundance in Betula nigra. Trees - Structure and Function 26: 525-533

Associated People:
Enrico Bonello

Abstract:
In managed settings, seedlings are often fertilized with the objective of enhancing establishment, growth, and survival. However, responses of seedlings to fertilization can increase their susceptibility to abiotic stresses such as drought. Seedlings acclimate to variation in soil resources by reallocating carbon among different physiological processes and compartments, such as above versus belowground growth, secondary metabolism, and support of ectomycorrhizal fungi (EMF). We examined the effects of nutrient and water availability on carbon allocation to above and belowground growth of river birch ( Betula nigra ), as well as partitioning among root sugars, starch, phenolics, lignin, and EMF abundance. As nutrient availability increased, total plant biomass and total leaf area increased, while percent root biomass decreased. Root sugars, total root phenolics and EMF abundance responded quadratically to nutrient availability, being lowest at intermediate fertility levels. Decreased water availability reduced total leaf area and root phenolics relative to well-watered controls. No interactions between nutrient and water availability treatments were detected, which may have been due to the moderate degree of drought stress imposed in the low water treatment. Our results indicate that nutrient and water availability significantly alter patterns of carbon allocation and partitioning in roots of Betula nigra seedlings. The potential effects of these responses on stress tolerance are discussed.


Wallis C, Eyles A, Chorbadjian RA, Riedl K, Schwartz S, Hansen R, Cipollini D, Herms DA, Bonello P (2011) Differential effects of nutrient availability on the secondary metabolism of Austrian pine (Pinus nigra) phloem and resistance to Diplodia pinea. Forest Pathology 41: 52-58

Associated People:
Enrico Bonello

Associated Projects:
Characterization of systemic induced resistance in Austrian pine

Abstract:
Nutrient availability can modulate the incidence and severity of plant diseases. We examined the effects of fertility on (i) host resistance and (ii) secondary metabolite production in the Pinus nigra Arnold –Diplodia pinea (Desm.) Kickx pathosystem. Following preconditioning of trees to one of three fertility levels for one growing season, phloem tissue of one branch was harvested for chemical analyses while another branch on the same whorl was inoculated with the fungus to assess resistance. Nutrient availability had concave and convex quadratic effects on concentrations of total monoterpenes and total phenolics respectively, but had no effect on fungal lesion lengths. Lesion lengths were negatively correlated with lignin, suggesting that this compound is an important factor in resistance. Counteracting effects of nutrient availability on phenolic and terpenoid pathways may explain why fertility had no effect on expression of disease resistance.


Nagle AM, McPherson BA, Wood DL, Garbelotto M, Bonello P (2011) Relationship between resistance to Phytophthora ramorum and constitutive phenolic chemistry in coast live oak. Forest Pathology 41: 464-469

Associated Projects:
Sudden Oak Death: mechanisms of oak resistance to Phytophthora ramorum

Abstract:
Sudden oak death, caused by Phytophthora ramorum, has resulted in high levels of coast live oak (CLO) mortality.  However, some CLO survive in areas with high disease pressure and may thus be resistant.  We tested the hypothesis that such field resistant trees contain constitutively higher levels of phenolics than susceptible trees.  Phloem was sampled from the trunks of two groups of trees (one previously inoculated, one naturally infected with P. ramorum) categorized over the course of several years as putatively resistant (PR, no symptoms), in remission (IR, showed symptoms but then recovered), and symptomatic (S).  Individual and total soluble phenolics from these trees were quantified.  There were no significant differences in individual or total soluble phenolics between groups of naturally infected trees.  However, inoculated PR and IR trees were characterized by higher constitutive levels of ellagic acid, a tyrosol derivative, and an unidentified phenolic than S trees.  Ellagic acid and tyrosol-like compounds in CLO phloem are promising resistance biomarker candidates.


Cipollini DF, Wang Q, Whitehill JGA, Powell JR, Bonello P, Herms DA (2011) Distinguishing defensive characteristics in the phloem of ash species resistant and susceptible to emerald ash borer. Journal of Chemical Ecology 37: 450-459

Associated People:
Enrico Bonello
Justin Whitehill

Associated Projects:
Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Abstract: We examined the extent to which three Fraxinus cultivars and a wild population that vary in their resistance to Emerald Ash Borer (EAB) could be differentiated on the basis of a suite of constitutive chemical defense traits in phloem extracts.  The EAB-resistant Manchurian ash (F. mandshurica, cv. Mancana) was characterized by having a rapid rate of wound browning, a high soluble protein concentration, low trypsin inhibitor activities and intermediate levels of peroxidase activity and total soluble phenolic concentration.  The EAB-susceptible white ash (F. americana, cv. Autumn Purple) was characterized by having a slow wound browning rate and low levels of peroxidase activity and total soluble phenolic concentrations.  An EAB-susceptible green ash cultivar (F. pennsylvanica, cv. Patmore) and a wild accession were very similar to each other on the basis of several chemical defense traits, and were characterized by having high activities of peroxidase and trypsin inhibitor, a high total soluble phenolic concentration, and an intermediate rate of wound browning.  Lignin concentration and polyphenol oxidase activities did not significantly differentiate resistant and susceptible species. Of 33 phenolic compounds separated by HPLC and meeting a minimum criterion for analysis, nine compounds were unique to Manchurian ash, five compounds were shared between all species, and four compounds were found in North American ashes and not in the Manchurian ash.  Principle components analysis revealed clear separations between Manchurian, white and the green ashes on the basis of all phenolics, as well as clear separations on the basis of quantities of phenolics that all species shared.  Variation in some of these constitutive chemical defense traits may contribute to variation in resistance to EAB in these species.


Chorbadjian RA, Bonello P, Herms DA (2011) Effect of the growth regulator paclobutrazol and fertilization on defensive chemistry and herbivore resistance of Austrian pine (Pinus nigra) and paper birch (Betula papyrifera). Arboriculture and Urban Forestry 37: 279-288

Associated People:
Enrico Bonello

Abstract:
The Growth/Differentiation Balance Hypothesis predicts that environmental factors that limit growth of plants more than their rate of photosynthesis should increase secondary metabolism and resistance to insects. Soil drench application of the plant growth regulator paclobutrazol slowed the growth of paper birch (Betula papyrifera) and Austrian pine (Pinus nigra) with no effect on photosynthesis. In response, foliar concentrations of condensed tannins (but not total phenolics) in birch increased as predicted, which increased birch resistance to gypsy moth (Lymantria dispar) and whitemarked tussock moth (Orgyia leucostigma), but only during the second season after treatment. In both years, there was a negative correlation between foliar concentrations of total phenolic and condensed tannins and growth of paper birch, which is consistent with the predicted trade-off between growth and defense. Conversely, in Austrian pine, paclobutrazol and fertilization did not have an effect on foliar concentration of tannins, phenolics, and terpenes, nor did the treatments have any effect on resistance to European pine sawfly (Neodiprion sertifer). Hence, the effects of paclobutrazol on tree growth, defensive chemistry, and insect resistance were species-specific and time sensitive.


Chen Y, Whitehill JGA, Bonello P, Poland TM (2011) Feeding by emerald ash borer larvae induces systemic changes in black ash foliar chemistry. Phytochemistry 72: 1990-1998

Associated People:
Enrico Bonello
Justin Whitehill

Associated Projects:
Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Abstract:
The exotic wood-boring pest, emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), has been threatening North American ash (Fraxinus spp.) resources, this being recognized since its first detection in Michigan, USA and Ontario, Canada in 2002. Ash trees are killed by larval feeding in the cambial region, which results in disruption of photosynthate and nutrient translocation. In this study, changes in volatile and non-volatile foliar phytochemicals of potted 2-yr-old black ash, Fraxinus nigra Marshall, seedlings were observed in response to EAB larval feeding in the main stem. EAB larval feeding affected levels of six compounds [hexanal, (E)-2-hexenal, (Z)-3-hexenyl acetate, (E)-b-ocimene, methyl salicylate, and (Z,E)-a-farnesene] with patterns of interaction depending upon compounds of interest and time of observation. Increased methyl salicylate emission suggests similarity in responses induced by EAB larval feeding and other phloem-feeding herbivores. Overall, EAB larval feeding suppressed (Z)-3-hexenyl acetate emission, elevated (E)-b-ocimene emission in the first 30 days, but emissions leveled off thereafter, and generally increased the emission of (Z,E)-a-farnesene. Levels of carbohydrates and phenolics increased overall, while levels of proteins and most amino acids decreased in response to larval feeding. Twenty-three amino acids were consistently detected in the foliage of black ash. The three most abundant amino acids were aspartic acid, glutamic acid, glutamine, while the four least abundant were a-minobutyric acid, b-aminoisobutyric acid, methionine, and sarcosine. Most (16) foliar free amino acids and 6 of the 9 detected essential amino acids decreased with EAB larval feeding. The ecological consequences of these dynamic phytochemical changes on herbivores harbored by ash trees and potential natural enemies of these herbivores are discussed.


Chen Y, Whitehill JGA, Bonello P, Poland TM (2011) Differential response in foliar chemistry of three ash species to emerald ash borer adult feeding. Journal of Chemical Ecology 37: 29-39

Associated People:
Enrico Bonello
Justin Whitehill

Associated Projects:
Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Abstract:
The emerald ash borer (EAB; Agrilus planipennis Fairmaire; Coleoptera: Buprestidae), is an exotic woodboring beetle that has been threatening North American ash (Fraxinus spp.) resources since its discovery in Michigan and Ontario in 2002. In this study, we investigated the phytochemical responses of the three most common North American ash species (black, green, and white ash) in northeastern USA to EAB adult feeding. Black ash was the least responsive to EAB adult feeding in terms of the induction of volatile compounds, and levels of only two (indole and benzyl cyanide) of the 11 compounds studied increased. In green ash, levels of two [(E)-β-ocimene and indole] of the 11 volatile compounds studied were elevated, while the levels of two green leaf volatiles [hexanal and (E)-2-hexenal] decreased. White ash showed the greatest response with an increase in levels of seven of the 11 compounds studied. Qualitative differences among ash species were detected. Among the phenolic compounds detected, ligustroside was the only one detected in all three species. Oleuropein aglycone and 2 unidentified compounds were found only in black ash; coumaroylquinic acid and feruloylquinic acid were detected only in green ash; and verbascoside hexoside was detected only in white ash. EAB adult feeding did not elicit or decrease concentrations of any selected individual phenolic compounds. However, although levels of total phenolics from black and green ash foliage were not affected by EAB adult feeding, they decreased significantly in white ash. EAB adult feeding elevated chymotrypsin inhibitors in black ash. The possible ecological implications of these findings are discussed.


Bai XD, Rivera-Vega L, Mamidala P, Bonello P, Herms DA, Mittapalli O (2011) Transcriptomic signatures of ash (Fraxinus spp.) phloem. Plos One 6: e16368

Associated People:
Enrico Bonello

Associated Projects:
Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Abstract:
Background: Ash (Fraxinus spp.) is a dominant tree species throughout urban and forested landscapes of North America (NA). The rapid invasion of NA by emerald ash borer (Agrilus planipennis), a wood-boring beetle endemic to Eastern Asia, has resulted in the death of millions of ash trees and threatens billions more. Larvae feed primarily on phloem tissue, which girdles and kills the tree. While NA ash species including black (F. nigra), green (F. pennsylvannica) and white (F. americana) are highly susceptible, the Asian species Manchurian ash (F. mandshurica) is resistant to A. planipennis perhaps due to their co-evolutionary history. Little is known about the molecular genetics of ash. Hence, we undertook a functional genomics approach to identify the repertoire of genes expressed in ash phloem. Methodology and Principal Findings: Using 454 pyrosequencing we obtained 58,673 high quality ash sequences from pooled phloem samples of green, white, black, blue and Manchurian ash. Intriguingly, 45% of the deduced proteins were not significantly similar to any sequences in the GenBank non-redundant database. KEGG analysis of the ash sequences revealed a high occurrence of defense related genes. Expression analysis of early regulators potentially involved in plant defense (i.e. transcription factors, calcium dependent protein kinases and a lipoxygenase 3) revealed higher mRNA levels in resistant ash compared to susceptible ash species. Lastly, we predicted a total of 1,272 single nucleotide polymorphisms and 980 microsatellite loci, among which seven microsatellite loci showed polymorphism between different ash species. Conclusions and Significance: The current transcriptomic data provide an invaluable resource for understanding the genetic make-up of ash phloem, the target tissue of A. planipennis. These data along with future functional studies could lead to the identification/characterization of defense genes involved in resistance of ash to A. planipennis, and in future ash breeding programs for marker development.


Nagle AM, Long RP, Madden LV, Bonello P (2010) Association of Phytophthora cinnamomi with white oak decline in southern Ohio. Plant Disease 94: 1026-1034

Associated People:
Enrico Bonello

Abstract:
A decline syndrome and widespread mortality of mature white oak tree (Quercus alba) associated with wet and low-lying areas has been recently observed in southern Ohio forests. Previous studies have isolated Phytophthora cinnamomi from white oak rhizospheres. In 2008 and 2009, P. cinnamomi population densities in two healthy and two declining white oak stands at Scioto Trail State Forest were quantified and potential roles of three environmental drivers of Phytophthora spp.–induced decline were assessed: soil texture, soil moisture, and topography. Significantly higher P. cinnamomi propagule densities were found in declining stands in both years but propagule densities were not associated with soil moisture content. Trends in population densities were not correlated with soil moisture or topographic position within field sites. There was a positive, exponential relationship between overall P. cinnamomi population levels and soil moisture on a seasonal scale in 2008 but not 2009. Sites with greater soil clay content were associated with greater decline. Effects of P. cinnamomi inoculum and periodic flooding on root health of 1-year-old potted white oak trees grown in native soil mixes in the greenhouse were examined. Root systems of potted oak were significantly damaged by soil inoculation with P. cinnamomi, especially under flooding conditions. Results of these studies support the hypothesis that P. cinnamomi is a contributing agent to white oak decline in southern Ohio.


Mittapalli O, Bai XD, Mamidala P, Rajarapu SP, Bonello P, Herms DA (2010) Tissue-specific transcriptomics of the exotic invasive insect pest emerald ash borer (Agrilus planipennis). PLoS ONE 5: e13708

Associated People:
Enrico Bonello

Associated Projects:
Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Abstract:
Background: The insect midgut and fat body represent major tissue interfaces that deal with several important physiological functions including digestion, detoxification and immune response. The emerald ash borer (Agrilus planipennis), is an exotic invasive insect pest that has killed millions of ash trees (Fraxinus spp.) primarily in the Midwestern United States and Ontario, Canada. However, despite its high impact status little knowledge exists for A. planipennis at the molecular level. Methodology and Principal Findings: Newer-generation Roche-454 pyrosequencing was used to obtain 126,185 reads for the midgut and 240,848 reads for the fat body, which were assembled into 25,173 and 37,661 high quality expressed sequence tags (ESTs) for the midgut and the fat body of A. planipennis larvae, respectively. Among these ESTs, 36% of the midgut and 38% of the fat body sequences showed similarity to proteins in the GenBank nr database. A high number of the midgut sequences contained chitin-binding peritrophin (248) and trypsin (98) domains; while the fat body sequences showed high occurrence of cytochrome P450s (85) and protein kinase (123) domains. Further, the midgut transcriptome of A. planipennis revealed putative microbial transcripts encoding for cell-wall degrading enzymes such as polygalacturonases and endoglucanases. A significant number of SNPs (137 in midgut and 347 in fat body) and microsatellite loci (317 in midgut and 571 in fat body) were predicted in the A. planipennis transcripts. An initial assessment of cytochrome P450s belonging to various CYP clades revealed distinct expression patterns at the tissue level. Conclusions and Significance: To our knowledge this study is one of the first to illuminate tissue-specific gene expression in an invasive insect of high ecological and economic consequence. These findings will lay the foundation for future gene expression and functional studies in A. planipennis.


Kleczewski NM, Herms DA, Bonello P (2010) Effects of soil type, fertilization and drought on carbon allocation to root growth and partitioning between secondary metabolism and ectomycorrhizae of Betula papyrifera. Tree Physiology 30: 807-817

Associated People:
Enrico Bonello

Abstract:
Paper birch (Betula papyrifera Marsh) seedlings were grown in a greenhouse in either subsoil or topsoil in factorial combination with two fertilization and drought regimes to investigate how different soil environments and nutrient availability drive belowground partitioning between growth, secondary metabolism and ectomycorrhizal (EM) associations, and impact drought tolerance of paper birch. Root and total seedling dry biomass, starch, soluble sugars, soluble phenolics, lignin and EM abundance were quantified. In unfertilized topsoil, total plant biomass and root biomass were approximately nine times higher than in unfertilized subsoil, but the root weight ratios did not differ between soils. Root soluble phenolics and lignin were higher in unfertilized subsoil than in unfertilized topsoil, whereas EM abundance was significantly higher in unfertilized topsoil than in unfertilized subsoil. In topsoil, fertilization decreased root biomass and EM abundance and increased root phenolics and lignin. In contrast, fertilization of subsoil increased root biomass but decreased root phenolics and lignin, while EM abundance was unaffected. In both soil types, fertilization reduced root weight ratios. Across soil types, EM abundance was negatively correlated with root soluble sugars, root phenolics and lignin, but this was driven mainly by the responses in the topsoil treatment. Our results show that soil fertility mediates carbon tradeoffs among defense, growth and EM associations.


Eyles A, Bonello P, Ganley R, Mohammed C (2010) Induced resistance to pests and pathogens in trees. New Phytologist 185: 893–908

Associated People:
Enrico Bonello

Abstract:
Tree resistance can be enhanced by a variety of biotic and abiotic inducers, including nonpathogenic and pathogenic microbes, and herbivores, resulting in enhanced protection against further biotic injury. Induced resistance (IR) could be a valuable tool in sustainable pest management. IR has been actively studied in herbaceous plant species, and, in recent years, in woody plant species, and is fast emerging as an intriguing, eco-friendly concept for enhancing tree resistance. However, before application of IR becomes possible, there is a need to increase our knowledge of the mechanisms of defence in forest trees. A richer understanding of these phenomena will play a critical role in developing sustainable integrated pest management strategies. This review summarizes our current knowledge of IR in forest trees, focusing on inducible defence mechanisms, systemic induction of resistance and phytohormone signalling networks. We conclude by discussing the potential advantages and limitations of applying IR-based management tools in forest systems.


Bonello P (2010) Potential of induced resistance as a tool for the management of pathogens and insects in trees – An ecological viewpoint. New Zealand Journal of Forestry Science 40: S15-S24

Associated People:
Enrico Bonello

Abstract:
Under natural conditions, forest ecosystems are usually stable, despite the constant presence of arthropods and pathogens inherently capable of killing their tree hosts. It is likely that the phenotypic plasticity of trees, which includes inducible resistance mechanisms against attacking organisms, plays a crucial role in these interactions. Systemic induced resistance may be a common and important phenomenon in forest trees, one that allows for balanced partitioning of available resources between growth and defence. However, such physiological tradeoffs are affected by environmental variables, such as resource availability (e.g. nutrients, water, light) as well as by silvicultural activities. There is also evidence that systemic induced resistance or its counterpart, systemic induced susceptibility, may be operative concurrently in the same tree, depending on the specific organs under attack. Lastly, all these host responses can be strongly modulated by systemic cross-effects between pathogens and/or insects.


Whitehill JGA, Opiyo SO, Koch J, Herms DA, Cipollini DF, Bonello P (2012) Interspecific comparison of constitutive ash phloem phenolic chemistry reveals compounds unique to Manchurian ash, a species resistant to emerald ash borer. Journal of Chemical Ecology 38: 499–511

Associated People:
Justin Whitehill

Associated Projects:
Mechanisms of ash (Fraxinus spp) resistance to the emerald ash borer (EAB, Agrilus planipennis Fairmare)

Abstract:
The emerald ash borer (Agrilus planipennis,EAB) is an invasive wood-borer indigenous to Asia and is responsible for widespread ash (Fraxinus spp.) mortality in the U.S. and Canada. Resistance and susceptibility to EAB varies among Fraxinus spp., which is a result of their coevolutionary history with the pest. We characterized constitutive phenolic profiles and lignin levels in the phloem of green, white, black, blue, European, and Manchurian ash. Phloem was sampled twice during the growing season, coinciding with phenology of early and late instar EAB. We identified 66 metabolites that displayed a pattern of variation, which corresponded strongly with phylogeny. Previously identified lignans and lignan derivatives were confirmed to be unique to Manchurian ash, and may contribute to its high level of resistance to EAB. Other compounds that had been considered unique to Manchurian ash, including hydroxycoumarins and the phenylethanoids calceolarioside A and B, were detected in closely related, but susceptible species, and thus are unlikely to contribute to EAB resistance of Manchurian ash. The distinct phenolic profile of blue ash may contribute to its relatively high resistance to EAB.