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1
Mitchell, Andrew George. "Population structures and interaction between the aggressive and non-aggressive subgroups of Ophiostoma ulmi." Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234084.
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Blumenstein, Kathrin. "Endophytic fungi in Elms : implications for the integrated management of Dutch Elm Disease." Thesis, Bangor University, 2015. https://research.bangor.ac.uk/portal/en/theses/endophytic-fungi-in-elmsimplications-for-the-integrated-management-of-dutch-elm-disease(3265a1c5-9910-4ed1-9d1e-c569b68d709d).html.
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Integrated pest management calls for new biocontrol solutions in management of forest diseases. Endophytic fungi that are commonly found in tree tissue may have potential in biocontrol. However, the links between endophyte status and disease tolerance are still unclear, and we know little about the mechanisms by which the endophytes can influence tree pathogens. The first goal of the thesis was to compare the endophyte status in elm (Ulmus spp.) trees with low vs. high susceptibility to Dutch elm disease (DED), caused by Ophiostoma fungi, and to find correlations between endophytes and the susceptibility pattern of the trees. The second goal was to investigate the potential mechanisms of antagonism by the endophytes towards the pathogen. Thus, endophytes were isolated from leaves, bark and xylem of elms that differed in DED susceptibility. The isolates were screened for their potential to counteract the pathogen in dual cultures. Selected strains were investigated using Phenotype MicroArrays to obtain the substrate utilization profiles that reflect the endophytes’ ability to compete with the pathogen for a nutritional niche. To test for a protective effect against the disease, promising isolates were injected into young elms. Preliminary analyses were done to identify the extracellular chemicals that some of the endophytes released into the growth medium. The results showed that the frequency and diversity of endophytes was higher in xylem of elms with high susceptibility to DED. Some endophytes deadlocked the pathogen with extracellular chemicals in vitro, while others had a faster growth rate. Several endophytes were able to utilize substrates more effectively than the pathogen. A preventive treatment with endophytes protected elms against DED, but the effect was unstable across years. Bioactive fungal extracts had a complex chemical profile, and the individual compounds in the extracts remain to be identified. Because endophytes antagonized the pathogen through different mechanisms, I suggest that an endophytebased biocontrol of DED could be best achieved through a synergistic effect of several endophyte strains.
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Cole, Thomas Edwin. "Molecular studies of virus-like dsRNAs in a diseased isolate of Ophiostoma novo-ulmi." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327031.
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Atkins, P. M. "Dutch elm disease : Some aspects of its biology and control." Thesis, University of Salford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376861.
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Bates, Malcolm Robert. "DNA polymorphism in the Dutch Elm disease fungus Ophiostoma ulmi." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/47767.
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Oghiakhe, Sunday. "Biology and Management of the Dutch Elm Disease Vector, Hylurgopinus rufipes Eichhoff (Coleoptera: Curculionidae) in Manitoba." Entomological Society of America, 2011. http://hdl.handle.net/1993/23811.
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Hylurgopinus rufipes, the native elm bark beetle (NEBB), is the major vector of Dutch elm disease (DED) in Manitoba. Dissections of American elms (Ulmus americana), in the same year as DED symptoms appeared in them, showed that NEBB constructed brood galleries in which a generation completed development, and adult NEBB carrying DED spores would probably leave the newly-symptomatic trees. Rapid removal of freshly diseased trees, completed by mid-August, will prevent spore-bearing NEBB emergence, and is recommended. The relationship between presence of NEBB in stained branch sections and the total number of NEEB per tree could be the basis for methods to prioritize trees for rapid removal.
Numbers and densities of overwintering NEBB in elm trees decreased with increasing height, with >70% of the population overwintering above ground doing so in the basal 15 cm. Substantial numbers of NEBB overwinter below the soil surface, and could be unaffected by basal spraying. Mark-recapture studies showed that frequency of spore bearing by overwintering beetles averaged 45% for the wild population and 2% for marked NEBB released from disease-free logs. Most NEBB overwintered close to their emergence site, but some traveled ≥4.8 km before wintering.
Studies comparing efficacy of insecticides showed that chlorpyrifos gave 100% control of overwintering NEBB for two years as did bifenthrin: however, permethrin and carbaryl provided transient efficacy. NEBB showed a gradual increase in development rate with increasing constant temperature. Lipid content of overwintering NEBB was higher in late fall than in mid-winter, which might show that depletion of fat reserves could jeopardize survival, but could be a result of conversion to cryoprotectants.
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Betsch, Brody Bly. "A Study of the Impacts of Dutch elm disease, Emerald ash borer, and Amur honeysuckle on the Flora of Rush Run Wildlife Area." Miami University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=miami1564514690185145.
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Björkroth, Jennie. "Effekter av naturvårdsgallring på förekomsten av lunglav på ädellövträd." Thesis, Linköpings universitet, Biologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-120089.
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Sun-exposed broad leaved deciduous trees have a great species diversity of epiphytic lichens. In Europe, these trees have decreased dramatically in number as wooded pastures have become overgrown with trees and bushes, and broad leaved deciduous stands have been replaced by planted coniferous trees. These are the main reasons for many lichens depending on deciduous trees being red-listed. Epiphytic lichens in overgrown areas could benefit from conservation thinning, but few studies have been performed on how this type of cutting affects the lichens. In a previous study, the presence of red-listed epiphytic lichens in a broad leaved deciduous forest was examined. After the study, thinning of trees and bushes was made. Here we study the effects of this thinning on Lobaria pulmonaria. We tested possible factors that may affect the growth of L. pulmonaria, and if there were any differences in incidence and vitality of the lichen between managed and unmanaged stands. Since Dutch elm disease and ash dieback are well spread in the area, we wanted to see if they also affected the growth of L. pulmonaria. There were no differences in incidence and growth between managed and unmanaged stands. The results were unexpected since other studies show that, for instance, increased sun exposure often has a great effect on the growth of lichens. Many elms and ashes were dead or dying and had a significant negative effect on the change of number of lobes and the lobe surface. The diseases of the trees can thus be assumed to be the greatest cause of why the lichens in the managed stand did not benefit from thinning.
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Meyerrose, Jana [Verfasser]. "Zuwachs an Wissen und Fertigkeiten durch EbM-Kurse und Prädiktoren für den Erfolg : eine multizentrische internationale Studie / Jana Meyerrose." Berlin : Medizinische Fakultät Charité - Universitätsmedizin Berlin, 2013. http://d-nb.info/1031096787/34.
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Schipper, Simone [Verfasser]. "Interaktive Öffentlichkeitsarbeit in der Landschaftsplanung : Potenziale und Strategien zur Förderung der Information, Kommunikation und Partizipation in der kommunalen Landschaftsplanung durch interaktive Öffentlichkeitsarbeit am Beispiel des Projekts "Interaktiver Landschaftsplan Königslutter am Elm (2002 - 2005)" / Simone Schipper." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2011. http://d-nb.info/1014253152/34.
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Proctor, Robert Henry. "Phytoalexins and dutch elm disease resistance." 1990. http://catalog.hathitrust.org/api/volumes/oclc/23379309.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1990.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 121-132).
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"Financial and Environmental implications of the Food Bank incorporating the woody biomass as a heating system for their new complex." Thesis, 2015. http://hdl.handle.net/10388/ETD-2015-12-2403.
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The City of Saskatoon is challenged with large quantities of wood wastes such as demolition wastes, construction wastes, and elm tree trims. It has also been recently found that some of the elm trees in Saskatoon might have been infected with the Dutch elm disease, hence, this would lead to the cutting down of trees. The cutting of the affected elm trees will definitely increase the quantities of wood wastes in Saskatoon. The City of Saskatoon might therefore develop the initiative to develop more landfills, as all wood wastes are usually deposited into the landfills. Landfills are usually not environmental friendly, hence, no one wants a landfill in his backyard.
Furthermore, the concerns about climate change is also a pressing issue around the world as individual countries most especially the industrialised countries are looking for means to reduce their carbon foot prints. The two issues discussed above have therefore developed the initiatives for renewable energy sources as an alternative to the burning of fossil fuel to produce energy. One of the common alternatives to burning of fossil fuel is the biomass fuel specifically the woody biomass fuel (wood chips). This project is therefore developed as one of the initiatives to evaluate the feasibility of wood chips as an energy source in Saskatoon.
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Nasmith, Charles George. "Molecular characteristics associated with the elm response in the Dutch elm disease complex." 2004. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=94672&T=F.
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Temple, Bradley Owen. "Molecular aspects of virulence in the causal agent of Dutch elm disease, Ophiostoma novo-ulmi." 2004. http://hdl.handle.net/1828/353.
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Dort, Erika. "Reprogramming the expression of the double-stranded RNA mitovirus OnuMV1c from the mitochondria to the cytoplasm in the fungal pathogen Ophiostoma novo-ulmi." Thesis, 2015. http://hdl.handle.net/1828/6578.
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Dutch elm disease (DED) is a debilitating wilt disease that has decimated elm populations globally. The current pandemic of this disease is caused by the ascomycete fungal pathogen Ophiostoma novo-ulmi. A number of strategies have been used to attempt to mitigate the effects of DED but none have met any sustainable success, and the disease continues to have severe ecological and economic impacts. Consequently, research focus has turned to the development of control strategies at the genetic level. One such genetic strategy is the use of naturally occurring fungal viruses (mycoviruses) to induce hypovirulence in their fungal hosts. Hypovirulence, or attenuation of fungal pathogenicity using mycoviruses, has been well studied in other systems but has yet to be developed for O. novo-ulmi.
A candidate virus, OnuMV1c, was found in an isolate of O. novo-ulmi (93-1224) at the western Canadian disease front and its genome was sequenced. OnuMV1c is a mitochondrial virus and has a 3.1 kb single-stranded positive RNA genome that encodes an RNA-dependent RNA polymerase (RdRp) involved in its replication as a double-stranded RNA molecule. It exists in O. novo-ulmi mitochondria in both its single-stranded and double-stranded forms.
Our research group identified OnuMV1c as a potential candidate for biological control of Dutch elm disease. Our long-term research goal is to use the virus as a means to activate the RNA interference pathway of O. novo-ulmi, leading to down-regulation of genes involved in pathogenicity. If OnuMV1c is engineered such that it carries an RNA interference cassette in addition to its own complement of genes, it could act as an enhanced hypovirus. RNA interference (RNAi) is a cytoplasmic process, and therefore in order to use OnuMV1c for RNAi the viral genome needed to be reprogrammed such that it could be expressed in the cytoplasm rather than the mitochondria. The objectives of my master’s research were to 1) genetically engineer OnuMV1c to express in the cytoplasm using a cDNA reverse genetics approach, and 2) test the functionality of the re-engineered cDNA OnuMV1c virus (MV1cCyt).
The first objective was accomplished by modifying codons in the RdRp sequence of OnuMV1c such that the sequence could be translated in the cytoplasm. This genetically engineered cytoplasmic version of OnuMV1c, named MV1cCyt, was flanked with exogenous promoter and terminator sequences to drive its transcription. The entire construct was engineered as a cDNA molecule and was cloned into the fungal transformation vector pAN7-1, which was used to transform O. novo-ulmi protoplasts.
The second objective was achieved through the use of strand-specific RT-PCR, a technique that allowed the detection of both the positive and negative strands of MV1cCyt. Results indicated that while four individual cell lineages contained MV1cCyt cDNA stably integrated into the nuclear genome, only one transformant was able to produce double-stranded MV1cCyt RNA. These results have important implications for the use of OnuMV1c as an engineered hypovirus and represent the first step towards the development of a biological control strategy for Dutch elm disease.Graduate
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Essenburg, Carol B. "Dutch elm disease and the vegetation composition of Manitoba's bottomland forests." 2009. http://hdl.handle.net/1993/3632.
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In Manitoba's bottomland forests, elms infected with Dutch elm disease are either left standing or removed. Removal creates gaps of various sizes in the canopy whereas dead trees left standing create smaller openings. In order to determine the impact of Dutch elm disease on the forest, 31 5-year old removal gaps, 43 openings beneath dead elms (openings were < 15 years old) and a 15 ha clearing (13 years old) were located along the Red River near Winnipeg, MB. In each of these areas and the adjacent undisturbed forest, vegetation was sampled using 5x5m plots and the point-quarter technique for trees, and 2x2m quadrats for shrubs and herbs. Woody species taller than 10cm and a diameter at breast height of less than 5cm were considered shrubs, and separated into three height classes (< 1m, 1-2m, > 2m). The herb stratum included all non-woody and woody plants less than 10cm tall. The 82 vascular understorey species with total cover values greater than 5% and bare ground were subjected to correspondence analysis. The closed forest consisted primarily of Ulmus americana, Acer negundo and Fraxinus pennsylvanica. Saplings of these species (< 1m tall) made up 70% of the shrub stratum in both disturbed and undisturbed areas. Fraxinus pennsylvanica saplings dominated all areas except the clearing, where a few young A. negundo occurred. All areas had approximately 50 vascular herb stratum species. Native taxa such as Laportea canadensis and Smilacina stellata predominated everywhere except in the clearing. The clearing was colonized by non-native weedy species such as Arctium lappa and Sonchus arvensis. It was clearly separated from closed forest plots in correspondence analysis, but the gap and dead elm forest plots were not. Gap and closed forest plots clustered by location, possibly reflecting the patchy nature of the forest or its past history. Dutch elm disease may cause the current Ulmus-Acer dominated forest to become dominated by F. pennsylvanica and A. negundo with U. americana present as only small, short-lived individuals. The impact of the loss of mature U. americana trees is dependent on its importance in the stand. Canopy openings created by the removal or death of a small number of U. americana have an understorey composition similar to the undisturbed forest. Tree regeneration is not occurring in the large clearing created by elm removal. "Weedy" herbs and Matteuccia struthiopteris are dominating the clearing.
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SROGONČÍK, Jakub. "Rozšíření jilmů v Novohradských horách a podhůří (historie a současnost)." Master's thesis, 2013. http://www.nusl.cz/ntk/nusl-154186.
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The aim of this thesis was to find out and map the occurrence of elm trees in Novohradske Mountains and in parts of the surrounding foothills. There is a natural occurrence of Wych elm (Ulmus glabra) on the respective territory which was confirmed by my research. I also managed to find six Field elm trees (Ulmus minor) that are not to be found on this territory naturally. A natural occurrence and purposeful growing of Wych elm tree (Ulmus glabra) is also proved in historical records dating as far back as 17th century when the respective territory was part of the Buquoy manor. During my field research I was able to find 40 localities with altogether 783 registered elm trees with the height of over 3 m. Researching the records of Forests of the Czech Republic, State Enterprise I also managed to find 10 more locations where I could register only 12 grown elm trees, since the remaining approximately 580 elm trees up to 5 m of height have been planted in the last decade and their numbers will be changing in the following decades as a result of 4 silvicultural measures. It mostly concerns elm trees that can be found in plastic protection or surrounded by forest fences against animal gnawing. It is interesting that there are several over aged specimen mostly in old alleys on the respective territory and all other elm trees do not exceed the estimated age of 50 years.
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Veilleux, Jonathan. "Establishment of Scolytus schevyrewi Semenov (Coleoptera: Curculionidae: Scolytinae) in the Prairies: life cycle, hosts and impact." 2012. http://hdl.handle.net/1993/8859.
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The banded elm bark beetle, Scolytus schevyrewi, was first observed in Canada in Alberta in 2006. In 2007, it was found in Manitoba and Saskatchewan. Its hosts include the American elm and so, it has the potential to transmit Dutch elm disease. The beetle was studied in six communities in 2009–2011 in Manitoba and Saskatchewan to learn about its biology in the Prairies. Baited sticky traps revealed that the adult flight period is from June until October, with a peak in late summer. Unbaited sticky traps and trap logs revealed that stressed Siberian elm is the preferred host. Although S. schevyrewi larvae overwintered successfully, 15% of the overwintering individuals emerged in the spring. The main impact of S. schevyrewi is expected to be the killing of stressed Siberian elms. Such trees should be removed to avoid population outbreaks that might result in attacks on healthy Siberian and American elms.
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Pinchback, Michael. "Construction and functional assignment of a manually annotated expressed sequence tag (EST) library from the pathogenic fungus Ophiostoma novo-ulmi." Thesis, 2006. http://hdl.handle.net/1828/2115.
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A genetic catalogue was generated from expressed sequence tags (ESTs) from the pathogenic filamentous fungus Ophiostoma novo-ulmi. Rather than full sequencing of the entire genome, fragments of each gene being actively expressed at a specific point in time were catalogued and annotated for identity and function. This catalogue represents a resource of considerable depth for the purposes of gene discovery, genetic regulation, protein expression, pathogenicity, and growth state studies. An online database was generated to serve as a powerful tool for downstream applications, facilitating and enhancing future research in all of these important areas of fungal biology.
The ascomycetous fungus Ophiostoma novo-ulmi represents an excellent model organism for genetic experimentation. A diversity of physiological functions, including dimorphism, pathogenicity, melanin biosynthesis, and glycoprotein secretion at high levels mean that principles elucidated from this fungus are likely of broad application. Ophiostoma novo-ulmi has been identified as the causative agent of Dutch elm disease, which has become an economic and horticultural pandemic in North America. As a result, the mechanisms of host-pathogen interaction of this fungus are of particular interest. Initial attempts at disruption of pathogenicity, most commonly by disruption of single genes identified as potential pathogenicity factors, have met with little success. As our understanding of the complexity and co-ordination of proteins involved with host-pathogen interaction deepens, the discovery of a single dominant pathogenicity gene is
becoming increasingly unlikely. As such, a broader genomics approach was employed to work towards identification of groups, or networks of genes that operate in a concerted manner, regulating pathogenicity or parasitic fitness.
A low redundancy library was constructed from Ophiostoma nova-ulmi complementary DNA, producing a total of 4386 readable expressed sequence tags (ESTs) from 5760 clones. Of these, 2093 sequences matched with sequences found in public databases while 2293 represented orphan sequences. Of the sequences in the former group, 1761 sequences matched with known proteins while 332 sequences matched with hypothetical/predicted proteins. Sequences matching known proteins included 880 singletons, corresponding to 49.97 % of the ESTs in this category. Extrapolating this proportion to the sequences matching hypothetical proteins estimated the number of singletons in this category to be 166. Similarly, 1835 orphan sequences were estimated to contain 917 unique sequences. Singletons matching entries in public databases (n=880) were manually annotated into functional categories as established by the Munich Information Centre for Protein Sequences (MIPS). Metabolism (21%), Protein Synthesis (10%), Subcellular Localization (10%), Biogenesis of Cell Components (8%), and Transcription (8%) categories were the most highly represented.
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Carneiro, Joyce Silva. "Towards Control of Dutch Elm Disease: dsRNAs and the Regulation of Gene Expression in Ophiostoma novo-ulmi." Thesis, 2013. http://hdl.handle.net/1828/4715.
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Ophiostoma novo-ulmi is the causal agent of Dutch elm disease (DED) which has had a severe impact on the urban landscape in Canada. This research program focused on developing molecular genetic strategies to control this pathogenic fungus.
The first strategy involved the development of RNA interference (RNAi) for the down-regulation of genes involved in pathogenicity. An efficient RNAi cassette was developed to suppress the expression of the endopolygalacturonase (epg1) locus which encodes a cell-wall degrading enzyme. This epg1-RNAi cassette significantly reduced the amount of polygalacturonase activity in the fungus and resulted in almost complete degradation of epg1 mRNA. The need for a native promoter to selectively down-regulate specific gene loci was addressed by developing a carbon-catabolite regulated promoter (alcA) to drive the expression of the epg1-RNAi cassette. The expression of an alcA-driven epg1-RNAi cassette resulted in the down-regulation of epg expression under glucose starvation but normal levels of expression in high glucose. The expression could therefore be controlled by culture conditions.
The second strategy explored the potential of using dsRNA viruses to vector disruptive RNAi cassettes. An isolate of O. novo-ulmi strain 93-1224 collected in the city of Winnipeg, was infected by two dsRNA mitoviruses which upon sequence characterization were named OnuMV1c and OnuMV7.
To assess the transmissibility of this dsRNA virus the infected isolate 93-1224 was paired with three naive isolates of the related fungi O. ulmi and O. himal-ulmi. Through the use of nuclear and mitochondrial markers it was determined that the virus OnuMV1c may not rely on mitochondrial fusion for transmission but may have a cytoplasmic transmission route.
This investigation of gene expression and manipulation has provided tools to help understand gene regulation in O. novo-ulmi. It has also added to our knowledge of mitoviruses, their transmission and potential use as a biological control. By enhancing our understanding of transmissible hypovirulence this work contributes to efforts to develop a new approach to target DED as well as a potential model for the control of other fungal diseases.Graduate
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Kassatenko, Irina. "Characterization of a new mitovirus OMV1c in a Canadian isolate of the Dutch Elm Disease pathogen Ophiostoma novo-ulmi 93-1224." Thesis, 2012. http://hdl.handle.net/1828/3949.
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The fungal pathogen Ophiostoma novo-ulmi is the causal agent of Dutch elm disease (DED) and has been responsible for the catastrophic decline of elms in North America and Europe. Double-stranded RNA (dsRNA) viruses are common to all fungal classes and although these viruses do not always cause disease symptoms, the presence of certain dsRNA viruses have been associated with reduced virulence (hypovirulence) in O. novo-ulmi. A new mitovirus was found in a Canadian isolate of O. novo-ulmi (93-1224) and has been named Ophiostoma mitovirus 1c (OMV1c). The positive strand of the dsRNA of OMV1c was 3,003 nucleotides in length and when the mitochondrial codon usage pattern was employed (mitochondria use UGA to encode tryptophan rather than as a chain terminator), a single large open reading frame (ORF) was found. This ORF had the potential to encode a protein of 784 amino acids, and revealed a high degree of nucleotide identity to genes encoding RNA-dependent RNA polymerase (RdRp) in other mitoviruses. The putative RdRp region of the newly characterized virus had the highest sequence similarity to Ophiostoma mitovirus 1b. The 5’- terminal sequence of the positive strand could potentially be folded into a double-stranded stem-loop structure with a free energy of 16.6 kcal/mol. Attempts to cure the O. novo-ulmi isolate 93-1224 of virus were unsuccessful. Screening of the re-cultured isolates for the presence of OMV1c revealed that it was still present in the fungus despite repeated hyphal tip transfer, a method known to cure cytoplasmic but not mitochondrial viruses. Based on the genome size, phylogenetic analysis, and the observation that infected isolates could not be cured, it was surmised that the virus was a member of the genus Mitovirus (family Narnaviridae). To assess the distribution of the virus in O. novo-ulmi at the disease front in Winnipeg, a small sample of thirteen isolates were screened for the presence of the new mitovirus. All proved to be negative for OMV1c, which indicated this dsRNA virus was rare and that isolate 93-1224 was the only isolate identified to date infected with OMV1c.
It was also discovered that the isolate O. novo-ulmi 93-1224 potentially harboured more than one virus. Electron microscopy of fractionated cells revealed the presence of two flexuous rod-shaped particles that may represent additional novel viruses.Graduate
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Meier, Fred G. "In vitro mansonone production and vascular staining in populations, trees within populations and individual progeny of Ulmus americana L. in relation to Dutch elm disease." 2009. http://hdl.handle.net/1993/3724.
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Dutch elm disease (DED) is a vascular wilt disease which has decimated populations of American elm (Ulmus americana L.) throughout North America. Mansonones are a family of phytoalexins found within the genus Ulmus and are thought to be involved in the resistance mechanism to DED. There have been no previous studies which have investigated the variation in production of mansonones within a large group of related elm. The purpose of this study was to investigate the production of mansonones within progeny from several parent trees within 6 populations of American elm located in Manitoba, Canada. In this study a method to measure mansonones by high performance liquid chromatography was developed with a shorter run time and a simple solvent system procedure than previously published by other researchers. Mansonone production varied significantly between genotypes. Production of mansonones within progeny from one parent within a population were significantly different than other parents within the same population. No significant differences in mansonone production were found between populations. Throughout the study when seedlings were measured for mansonone production through in vitro callus cultures it was found that mansonones were also produced in control treatments. Further experiments performed to address this problem revealed that mansonone production was initiated approximately at the same time callus tissue was formed. No previous studies have reported this incidence. Vascular staining, a symptom of DED, within progeny varied significantly between parents and populations. When mansonone production and vascular staining were compared among progeny from the same parent trees and populations, no correlation was found (r2 = 0.01). At the juvenile stage, it appears that neither mansonone production nor vascular staining is an adequate indicator of resistance. This is the first study to show large differences in the production of mansonones over such a large study group. Future research on mansonone production and DED resistance must concentrate on more mature material which can show visual symptoms of DED more accurately.