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Sixty-two natural cankers on branches and main stems of three 16-year-old grafted American chestnut trees at the Lesesne State Forest were sampled for Cryphonectria parasitica. Cankers were sampled in 1996 and 1997 at various distances from the main stem zone on the grafts (ground to 183 cm) that was inoculated in 1982 and 1983 with a mixture of dsRNA-containing white and pigmented hypovirulent strains. Grafted trees exhibited a high level of blight control, and all bark cores extracted from cankers on the grafted trees showed superficial necrosis. Bark cores extracted from these cankers yielded 156 isolates of C. parasitica. Fifty-three of these isolates were white, and 103 were pigmented. The farthest canker containing a white isolate was located 564 cm from the zone inoculated with hypovirulent strains (H-inoculated zone). The number of white isolates recovered per canker on the grafted trees near the H-inoculated zone (< 0.5 maximum sampling distance) was significantly greater (P=0.0039) than the number of white isolates recovered per canker on the grafted trees far from the H-inoculated zone (>0.5 maximum sampling distance). Lloyd's index of patchiness value for the frequency of white isolates in cankers was 1.36, indicating that white isolates were slightly aggregated in cankers. White isolates of C. parasitica were found in two of seven artificially established cankers 5 months after inoculation with a pigmented virulent strain (WK). Thirteen of 14 pigmented isolates collected from these cankers after 5 months were compatible with WK in vegetative compatibility (VC) tests. Eight of 25 white isolates recovered 5, 11, and 50 months after WK inoculation converted the pigmented WK strain to the white hypovirulent phenotype in vitro. Sixty-five pigmented isolates collected from natural cankers were paired in VC assays, revealing 28 VC groups. All 11 white isolates of C. parasitica assayed contained a 12.7 kb dsRNA in high concentrations. None of 48 pigmented isolates assayed contained dsRNA. All white isolates tested in virulence trials on American chestnut stems in a forest clearcut were hypovirulent, based on low canker severity indices. Little or no dissemination of white strains to cankers on the American chestnut stump sprout clusters, which surround the grafted trees, was found. In the future, to maximize spread of white hypovirulent strains on American chestnut trees, it may be beneficial to re-inoculate trees with hypovirulent strains farther up the main stem after substantial tree growth has occurred. / Master of Science

Plant-associated microbes (collectively the microbiome) are important contributors to plant health. They are known to play roles in increasing yield via improving stress tolerance, promoting growth, and suppressing the activity of plant pathogens. We investigated the wheat seed-head microbiome (phytomicrobiome) as a potential source of resistance to Fusarium head blight (FHB), or scab. FHB is a devastating disease in wheat, and other cereal grains, that causes losses in both quantity, through reduced yield, and quality of grain, through the production of toxins such as Deoxynivalenol. Efforts to combat FHB have focused primarily on breeding cultivars with resistance and applying fungicides. However, new resources for combatting FHB may lie in microbiome-plant interactions. To explore host-microbiome-pathogen interactions, we used field trials to characterize the seed head bacterial community (16S rRNA gene amplicons) across planting locations, host resistance genotypes, varieties, and plant development stages. We identified bacterial amplicon sequence variants (ASVs) present in each sample and then examined ASV community composition based on our variables. Characterizing bacterial relative abundance across samples, we identified 9,063 ASVs. These ASVs clustered according to plant developmental stages or maturity plant, location, and host genotype, but not by variety or maturity group. First, comparing plants at the pre-flowering versus mature grain-head stage, we found that both bacterial community richness and evenness changed significantly. In addition to these developmental changes, we found that bacterial community structure changes across locations, even between locations. Finally, we found that, in the presence of the pathogen, ASVs cluster by host resistance genotype, and that there are important taxonomic groups that are differentially abundant in the presence of the pathogen. Overall, we found that the wheat grain-head microbiome is shaped by environment-host-pathogen interactions, and that these interactions lead to differential abundance of particular community members that may be important in the management of FHB. / Master of Science in Life Sciences / Plant associated microbes are important contributors to plant health. They are known to play roles in increasing yield via improved stress tolerance, promoting growth, and suppressing plant disease. We investigated the wheat grain-head microbial communities as a source of disease resistance. The disease is called Fusarium Head Blight (FHB) and is caused by Fusarium graminaerum. FHB is a devastating disease in wheat and other cereals, causing losses, through reduced yield and quality through the production of toxins that prohibit use of the grain. To combat FHB, research has focused on developing plants that have resistance and the application of chemical fungicides. However, new resources for combating FHB may lie in the interactions between plants and microbes. This research is focused on identifying microbes that naturally interact with the plant, and how the pathogen, Fusarium, interacts with these beneficial microbes. In field trials, we characterized the microbial community by DNA sequencing technologies across locations, wheat with varying levels of genetic resistance, and wheat developmental stages. First, between the wheat kernel samples of pre-flowering and maturity, we found significant differences in microbial community. Consistent with other studies we found that the largest changes in microbial community composition across different growing locations. Finally, we found an interaction between the grain head microbiome and host resistance state when plants were exposed to the pathogen. Overall, we find that the wheat grain head microbiome is shaped by growing location and through interactions with the plant host and pathogen.

Blight and the elimination thereof have profoundly impacted urban areas. In Colony Park/Lakeside (Austin, Texas), community leaders and members of the local neighborhood association have come together to mitigate and reverse social, economic, and physical symptoms of blight in their neighborhood. Following the approval of a HUD Community Challenge Planning Grant application that was submitted by the Austin Neighborhood Housing and Community Development (NHCD) department, these individuals utilized the media attention surrounding the grant to campaign for code enforcement, landlord-tenant accountability, policing, and the clean-up of illegal dumping in the area. Moreover, after much ado between residents and City workers, the neighborhood association devised a community-focused partnership with the City to ensure that current residents would reap the benefits of the planning process and help define the collective will and interests of the community. Utilizing publicly available data and first-hand knowledge from one City code compliance investigator and local residents, this report attempts to provide a blight indicator analysis of the Colony Park/Lakeside planning area as defined by NHCD. In other words, this report uses quantitative data to create descriptive maps of current neighborhood conditions with particular attention to code violations and community discussions surrounding them. The results of this work are intended to shed light on where resources should be directed to further research in the area and to resolve issues that threaten the health, safety, and viability of the neighborhood today. / text

Thesis (M.S.)--Mississippi State University. Department of Entomology and Plant Pathology. / Title from title screen. Includes bibliographical references.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Fusarium Ear Blight (FEB) is a globally important floral disease of cereal crops such as wheat, maize and barley. The predominant causal agents of FEB disease of wheat in the UK are Fusarium culmorum and F. graminearum. Wheat infecting isolates of both of these fungal species infect the floral and silique tissues of the model plant Arabidopsis thaliana, providing a tractable model for analysis of factors determining plant susceptibility or resistance to Fusarium infection. The effect of F. culmorum infection on the metabolic composition (metabolome) of Arabidopsis pedicel tissue following silique inoculation was investigated in a collection of mutants with altered defence responses to F. culmorum and/or other plant pathogens, using a 1¬H-NMR/ESI-MS (+/-) triple fingerprinting approach. These mutants showed differing metabolomic fingerprints in the absence of F. culmorum infection, as well as differences in accumulation or depletion of metabolites in response to F. culmorum colonisation. A number of metabolites were also identified which were induced by F. culmorum infection irrespective of plant genotype. Quantitative differences in compound accumulation were also observed between genotypes in the Columbia and Landsberg erecta accessions following F. culmorum infection. One of the genotypes investigated was eds11, which has enhanced susceptibility to F. culmorum floral infection. Mapping of the mutation responsible for the eds11 phenotype was initiated using an isogenic mapping by sequencing approach. This resulted in a list of potential candidates for the EDS11 gene. Additional Arabidopsis mutants were investigated for altered defence responses to F. culmorum floral infection. Multiple mutant alleles of the Arabidopsis homoserine kinase gene DMR1 were found to have enhanced resistance to F. culmorum silique infection and rosette leaf colonisation, associated with accumulation of homoserine in siliques and delayed leaf senescence. Exogenous homoserine application enhanced resistance in wild type and dmr1 plants. Collectively, these findings form a novel contribution to current knowledge of the Fusarium-Arabidopsis interaction. This may have applications for improvement of FEB resistance in cereals.

O uso de plantas resistentes no controle da requeima causada por Phytophthora capsici L. atende à crescente demanda de uma agricultura sustentável e a preocupação com a saúde humana e com o ambiente. Um isolado de P. capsici foi utilizado a fim de comparar a interação em nível histológico, com o auxílio de microscopia de luz, entre esse patógeno e quatro genótipos de Capsicum annuum com diferentes níveis de resistência, sendo dois resistentes (AF2169 e AF2191), um moderadamente resistente (AF6529) e um suscetível (AF1418) para a melhor compreensão da forma de colonização e dos mecanismos de resistência encontrados na planta. A microscopia de luz permitiu uma visão geral sobre o desenvolvimento do patógeno e as respostas do hospedeiro após a inoculação com P. capsici. Em conclusão, nota-se que AF1418 e AF6529, ao final de 72 HAI, comportaram-se de forma semelhante à inoculação, enquanto os genótipos AF2169 e AF2191 apresentaram diferenças tanto quanto a forma de crescimento do patógeno quanto a respostas de defesa desenvolvidas pela planta. Em ambos os genótipos resistentes não houve o desenvolvimento de haustórios ou vesículas de infecção, apesar de ter ocorrido a colonização intracelular em AF2169. Mesmo não havendo o desenvolvimento de sintomas nos genótipos resistentes, nos cortes histológicos observados, aparentemente, os mecanismos de defesa desenvolvidos pelo AF2191 foram mais eficientes, uma vez que a planta conseguiu impedir a colonização intracelular do patógeno. Experimentos posteriores devem ser realizados para quantificar suberina, espécies reativas de oxigênio e compostos fenólicos, a fim de validar os resultados observados em microscopia de luz com os testes histoquímicos, além de verificar o papel desses compostos na defesa dos genótipos analisados. / The use of resistant plants to control blight caused by Phytophthora capsici L. attend the growing demand for sustainable agriculture and concern for human health and the environment. A Phytophthora capsici isolate was used in order to compare the interaction at the histological level, with the aid of light microscopy, between this pathogen and four genotypes of Capsicum annuum with different levels of resistance, two resistant (AF2169 e AF2191), one moderately resistant (AF6529) and one susceptible (AF1418) for a better understanding of the mode of colonization and mechanisms of resistance found in the plant. Light microscopy allowed an overview of the development of the pathogen and host responses after inoculation with P. capsici. In conclusion, AF1418 and AF6529, at the end of 72 HAI, behaved similarly to inoculation. While the AF2169 and AF2191 genotypes showed differences as much as the form of growth of the pathogen as to defense responses developed by the plant. In both resistant genotypes there was no development of haustoria or infection vesicles, despite the occurrence of intracellular colonization in AF2169. Even without the development of symptoms in the resistant genotypes, in the observed histological sections, the defense mechanisms developed by AF2191 were apparently more efficient, since the plant was able to prevent the intracellular colonization of the pathogen. Subsequent experiments should be carried out to quantify suberin, reactive oxygen species and phenolic compounds in order to validate the results observed in light microscopy with the histochemical tests, as well as to verify the role of these compounds in the defense of the analyzed genotypes.

Ascochyta blight, caused by Ascochyta rabiei (Pass.) Labrousse, is one of the most destructive diseases of chickpea (Cicer arietinum L.) worldwide. Despite the existence of highly resistant uncultivated genotypes, attempts to develop cultivars with a high level of durable resistance have been unsuccessful. This study investigated the chickpea defence response to A. rabiei using a functional genomics approach, which has the capacity to improve the overall understanding of the coordinated defence response at a molecular level. An existing cDNA library was used to generate a resource of Expressed Sequence Tags (ESTs) that, after clustering, comprised 516 unigenes. The unigenes were functionally annotated resulting in the identification of 20 specific defence-related unigenes, as well as numerous transcripts with possible involvement in the coordination of defence responses. To explore the expression patterns of the defence-related unigenes in an A. rabiei resistant and susceptible genotype, the unigenes were employed as probes in microarrays. Resulting expression data was analysed to identify differentially expressed unigenes over a time-course after infection. Comparison of the expression profiles from the resistant and susceptible genotype identified three putative genes that were exclusively up-regulated in the resistant genotype, thus may be involved in an effective defence response. Considering that a defence response can involve hundreds of genes, the entire set of chickpea unigenes were used to construct large-scale microarrays. To supplement the chickpea probes, 156 putative defence-related grasspea (Lathyrus sativus L.) ESTs and 41 lentil (Lens culinaris Med.) Resistance Gene Analogs (RGAs) were also included. Expression profiles for three chickpeas and one wild relative were generated over a time course. 97 differentially expressed ESTs were identified using a robust experimental system that included confirmation by quantitative RT-PCR. The results indicated that genes involved in the active defence response were similar to those governed by R-gene mediated resistance, including the production of reactive oxygen species and the hypersensitive response, down-regulation of 'housekeeping' gene expression, and expression of pathogenesis-related proteins. The comparison between resistant and susceptible genotypes identified certain gene expression 'signatures' that may be predictiv e of resistance. To further characterise the regulation of potential defence-related genes, the microarray was used to study expression profiles of the three chickpea genotypes (excluding the wild relative) after treatment with the defence signalling compounds, ethylene (E), salicylic acid (SA), and jasmonate (JA). 425 ESTs were differentially expressed, and comparison between genotypes revealed the presence of a wider range of inducible defence responses in resistant genotypes. Linking the results with the previous microarray results indicated the presence of other pathogen-specific signalling mechanisms in addition to E, SA and JA. The lower arsenal of defence-related gene expression observed in the susceptible genotype may be a result of 'breaks' in the pathways of defence-related gene activation. To draw together the findings of all experiments, a model was constructed for a hypothetical mechanism of chickpea resistance to A. rabiei. The model was synthesised based on the evidence gathered in this study and previously documented defence mechanisms in chickpea, and identified signal transduction as a key to resistance.

Field pea (Pisum sativum L.) is highly susceptible to ascochyta blight, primarily caused by the pathogen Mycosphaerella pinodes (Berk. & Blox.) Vestergr. Grasspea (Lathyrus sativus L.) has been reported to possess a moderate level of resistance to ascochyta blight caused by M. pinodes. The work reported in this thesis aimed to develop the various techniques that would be required to transfer ascochyta blight resistance from grasspea into field pea via somatic hybridisation. This thesis also assesses the feasibility of achieving this goal. Field pea shoot cultures were established on hormone-free MS medium, and a protoplast isolation protocol developed for both species. Grasspea shoot cultures were established on both RL and SSB8 medium. Friable grasspea callus was achieved on media supplemented with 2,4-D in the range 4.523 µM, whereas kinetin tested at any concentration did not appear to influence callus growth. A suspension culture of grasspea was developed for the first time, in B5 medium supplemented with 4.5 µM 2,4-D and 0.5 µM kinetin. Grasspea protoplasts were isolated from both in vitro seedlings and suspension cultures. Protocols for hybrid shoot culture on KM8p medium were developed via organogenesis and somatic embryogenesis.