Plant Pathology Masters Theses

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Assessing Cereal Aphid Diversity and Barley Yellow Dwarf Risk In Hard Red Spring Wheat and Durum
(North Dakota State University, 2018) Haugen, Samuel Arthur McGrath
Barley yellow dwarf (BYD), caused by Barley yellow dwarf virus and Cereal yellow dwarf virus, and is a yield limiting disease of small grains. A research study was initiated in 2015 to identify the implications of BYD on small grain crops of North Dakota. A survey of 187 small grain fields was conducted in 2015 and 2016 to assess cereal aphid diversity; cereal aphids identified included, Rhopalosiphum padi, Schizaphis graminum, and Sitobion avenae. A second survey observed and documented field absence or occurrence of cereal aphids and their incidence. Results indicated prevalence and incidence differed among respective growth stages and a higher presence of cereal aphids throughout the Northwest part of North Dakota than previously thought. Field and greenhouse screenings were conducted to identify hard red spring wheat and durum responses to BYD. Infested treatments in the greenhouse had significantly lower number of spikes, dry shoot mass and yield.
Augmenting Fungicidal Activity of Tetraconazole with Chemosensitization Agents for Cercospora Leaf Spot Management
(North Dakota State University, 2017) Metz, Nicholas James
Cercospora beticola (Sacc.) is the causal agent of Cercospora leaf spot (CLS). CLS is considered to be one of the most destructive foliar diseases of sugar beet in the world. CLS is managed in part through resistant cultivars, crop rotation, and cultural practices, but timely fungicide applications are necessary to manage disease effectively. Heavy reliance on fungicides to manage CLS has led to the development of resistance to multiple classes of fungicides. The most widely used class of fungicides is the demethylation inhibitors (DMIs). DMI-resistant C. beticola isolates have been increasing in incidence over the past decade. Chemosensitization agents (CAs) are compounds that have little to no antifungal activity, but may increase efficacy of commercial fungicides when co-applied. CAs could lead to better management of CLS and reduced production costs.
Biology and Management of Fusarium Species on Sugar Beet
(North Dakota State University, 2017) Lai, Xiao
Minnesota and North Dakota together produce about 51% of the beet sugar in the United States of America. Fusarium diseases caused by Fusarium oxysporum f. sp. betae and F. secorum on sugar beet cause significant reduction in both root yield and sucrose concentration. This research was conducted to determine the best inoculation methods to induce Fusarium diseases on sugar beet seeds and plants and to evaluate fungicides for their efficacy at controlling Fusarium diseases in greenhouse conditions. The use of Fusarium colonized barley seeds in close proximity to sugar beet seeds and seedlings caused similar level of disease severity as the standard root-dipping method, and reduced the time for evaluation by directly inoculating seeds and 4-leaf stage plants rather than using older plants which have to be transplanted into new pots. Pydiflumetofen and metconazole fungicides used in-furrow have the potential to provide effective control of Fusarium diseases on sugar beet.
Characteristics and Host Range of a Novel Fusarium Species Causing Yellowing Decline of Sugarbeet
(North Dakota State University, 2013) Villamizar-Ruiz, Johanna Patricia
In 2008, a novel and distinct Fusarium species was reported in west central Minnesota causing early-season yellowing and severe decline of sugarbeet. This study was conducted to (i) establish optimum conditions for fungal growth and (ii) determine the host range of the novel Fusarium. The optimum temperature for fungal growth is 24°C and root injury is not needed to penetrate, infect, and cause disease of sugarbeet plants. Of the fifteen common crops and weeds tested for susceptibility to the new Fusarium sp. in field and greenhouse trials, disease symptoms were only observed in sugarbeet. Host range plants were tested for the presence of latent infection by root isolations and PCR. The pathogen was only present in canola and sugarbeet. The results suggest that canola has implications in the sugarbeet production system and management strategies for the novel Fusarium species. The name and description of the new Fusarium sp. is pending.
Characterization and Detection of Bacterial Pathogens of Common Bean
(North Dakota State University, 2022) Nelson, Katie
Common bacterial blight (CBB) (Xanthomonas axonopodis pv. phaseoli (Xap) and X. fuscans pv. fuscans (Xff), halo blight (Pseudomonas savastanoi pv. phaseolicola (Psp)), and bacterial brown spot (P. syringae pv. syringae (Pss)), are yield-limiting diseases of common bean in North Dakota and Minnesota. The objectives of this research were to optimize a multiplex quantitative PCR (qPCR) assay for rapid detection and quantification of four bacterial pathovars in common bean seed, leaf, and pod tissue; determine the aggressiveness of Xap and Xff isolates; and determine the race types of Psp isolates in North Dakota and Minnesota. A fourplex qPCR assay was optimized, and novel primers and probe were designed for pathovar-specific detection of Pss. Significant differences were observed in Xap/Xff aggressiveness across isolates evaluated and in susceptibility of the differential lines (P <.0001). The 60 Psp isolates were identified as Race 6, the predominant race in the region.
Characterization of Cytochrome B from European Field Isolates of Cercospora Beticola with Quinone Outside Inhibitor Resistance
(North Dakota State University, 2012) Birla, Keshav
Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on fungicides including quinone outside inhibitor (QOI) fungicides. We collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the QOI fungicide pyraclostrobin. To gain an understanding of the molecular basis of QOI resistance, we cloned the full-length coding region of Cbcytb. All tested QOI-resistant isolates harbored a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay was developed to discriminate QOI-sensitive and QOI-resistant isolates based on the G143A mutation. Our results indicate that QOI resistance has developed in some European C. beticola populations in Italy and monitoring the G143A mutation is an essential fungicide resistance management strategy.
Characterization of Effector Encoding Genes from the Novel Sugar Beet Pathogen Fusarium Secorum
(North Dakota State University, 2015) Bian, Zhuyun
A new disease of sugar beet, named Fusarium yellowing decline, was recently found in in the Red River Valley of MN and ND. This disease is caused by a novel pathogen named Fusarium secorum. Pathogens such as F. secorum secrete proteins during infection called ‘effectors’ that help establish disease. Since pathogenicity and disease development may depend on effector proteins produced by F. secorum during infection, effector protein identification furthers our understanding of the biology of this important pathogen. A list of 11 candidate effectors was generated previously. In this study, to characterize putative effectors, we developed a transformation system using polyethylene glycol–mediated transformation. Several mutant lines were created with an effector deleted from the genome using a split-marker knock-out strategy. To explore their role in pathogenicity, mutant strains have been inoculated to sugarbeet and compared to WT F. secorum.
Characterization of North Dakota Hard Red Spring Wheat for Stem and Stripe Rust Resistance
(North Dakota State University, 2022) Kim, YongJae
Puccinia graminis f. sp. tritici (Pgt) and Puccinia striiformis f. sp. tritici (Pst) are causal agents of devastating wheat stem and stripe rust diseases, respectively. Both diseases sporadically occur in North Dakota (ND), and stripe rust incidence has been increasing in the Midwest of United States over the last decade. Complete information of rust resistance in ND hard red spring wheat (HRSW) germplasm is not well-established. This study focused on the phenotypic characterization of ND HRSW germplasm for stripe and stem rust resistance and the identification of existing and novel rust resistance genomic loci in this population through genome-wide association study (GWAS). The GWAS has identified several marker-trait associations (MTAs) for both all-stage and adult plant resistance for each rust disease. This information will support the deployment of these resistant loci in wheat varieties by the NDSU HRSW breeding program.
Characterization of Programmed Cell Death Responses Involved in Disease Resistance/Susceptibility Responses in Barley
(North Dakota State University, 2015) Sager-Bittara, Lauren Paige
The plant innate immune system relies on regulated programmed cell death (PCD) responses which provide resistance against biotrophic fungal pathogens and are utilized by necrotrophic pathogens. The gene-for-gene interactions leading to resistance against biotrophs has been co-evolving over millions of years and provides many targets for necrotrophic pathogens to subvert the plants PCD for their benefit. Two PCD pathways involved in plant immunity were characterized. The first, nec3, appears to control runaway PCD in response to infection by many pathogens who mainly elicit pathogen or damage associated molecular pattern (PAMP or DAMP) triggered immunity. The nec3 mutant was mapped to chromosome 6H and a pool of candidate genes were identified by RNAseq. The second, Rcs5, is a dominant susceptibility gene or a putative necrotrophic effector triggered susceptibility (NETS) target that confers susceptibility to Cochliobolus sativus. The candidate Rcs5 genes are three Wall Associated Kinases (WAKs) found on chromosome 7H (1).
Characterization of Sensitivity of Sclerotinia Sclerotiorum Isolates from North Central U.S. to Thiophanate-Methyl and Metconazole
(North Dakota State University, 2013) Ameen, Gazala
Sclerotinia sclerotiorum (Lib.) de Bary causes Sclerotinia stem rot on canola and many other crops of economic importance in the U.S. SSR is primarily controlled with fungicides applied at flowering time. Most fungicides currently used to control SSR can promote resistance buildup in their target populations making monitoring of sensitivity important. In this study the reaction of S. sclerotiorum to thiophanate-methyl (TM) and metconazole (MTZ) was characterized. Samples collected in several states of north central U.S. were used. Three and ten isolates were considered to be moderately insensitive to TM and MTZ, respectively. Greenhouse trials indicated, however, that diseases caused by these isolates could be effectively controlled using currently recommended doses of each compound. In vitro sensitivity to TM was temperature dependent. A previously unreported mutation at codon E111D in the β-tubulin gene of a TM-moderately insensitive isolate was identified.
Determination of Disease Impacts on Sunflower Yield
(North Dakota State University, 2020) Hansen, Bryan Charles
Diseases that infect sunflower frequently occur in North Dakota, but the impact they have on yield is unclear. The objectives of this research are to 1) evaluate fungicide efficacy, application timing and yield impact of Phoma black stem of sunflower and 2) determine the impact of diseases on sunflower yield in North Dakota and Minnesota. Results of 14 fungicide trials conducted between 2017 and 2019 showed that yield losses to Phoma black stem were infrequent, but the disease could be managed by application of several available and efficacious fungicides applied at growth stage R1. Analysis of survey data collected over 11 years from 1,003 sunflower fields revealed that when diseases were determined to be a production-limiting factor, mean yield was 427 kg/ha less than in fields where no was production-limiting factor was reported. Results of these studies may help sunflower growers make decisions that optimize yield on their farms.
Developing a New Inoculation Method, and Evaluating the Potential Biological Control of Rhizoctonia solani by Penicillium pinophilum on Sugar Beet
(North Dakota State University, 2020) Haque, Md Ehsanul
Rhizoctonia solani causes damping-off, and root and crown rot of sugar beet (Beta vulgaris L.) and overwinters as sclerotia and mycelia. Research was conducted to determine how best to produce large quantities of sclerotia and mycelia in vitro, and compare their pathogenicity with traditionally used colonized barley grains to sugar beet in vitro and in vivo. The greatest number of sclerotia was produced on amended clarified V8 medium and sclerotia caused more disease compared to barley inoculum in the greenhouse. The bio-control potential of Penicillium pinophilum on R. solani AG2-2 on sugar beet was evaluated in vitro and in vivo. Results showed that the presence of P.pinophilum with R.solani reduced damping-off by 75% and thus have the potential to be developed as a bio-control agent for this pathogen.
Development of Quantification and Diagnosis Methods for Cereal Bacterial Leaf Streak Pathogens
(North Dakota State University, 2022) Hong, Eunhye
Bacterial leaf streak (BLS) has been a major disease on wheat and barley in the Northern Great Plains. It is caused by Xanthomonas translucens pv. undulosa (Xtu) on wheat and X. translucens pv. translucens (Xtt) on barley. Many questions remain unclear on pathogen biology and BLS epidemiology. Based on previous study, I identified an Xtu/Xtt specific region and established a qPCR quantification method for the bacterial pathogens. The method was shown to be effective to detect and quantify the bacterial pathogen in seeds and leaves. In addition, molecular markers were developed to differentiate Xtu and Xtt. Those markers were successfully used to characterize a collection of X. translucens strains into Xtu or Xtt. The results were also confirmed by pathogenicity tests on wheat and barley. The efficient Xtt/Xtu quantification and differentiation methods will be powerful tools to study disease epidemiology and host pathogen interaction for the two bacterial pathogens.
Downy Mildew of Sunflowers: Establishment of Baseline Sensitivity to Azoxystrobin and Monitoring for the Development of Fungicide Resistance and Plasmopara Halstedii Virulence Phenotype Changes
(North Dakota State University, 2017) Gilley, Michelle A.
Downy mildew, caused by Plasmopara halstedii (Farl.) Berl. and de Toni, is an economically important disease in cultivated sunflowers, Helianthus annuus L. The objectives of this study were to determine disease pressure in North Dakota and South Dakota, determine the virulence phenotypes in the pathogen population, determine the baseline sensitivity to azoxystrobin and evaluate select isolates for fungicide insensitivity. While downy mildew was present in many fields, incidence was typically low. To determine virulence phenotypes, selected isolates were evaluated on an expanded set of differential lines. New virulence was found to the Pl8 resistance gene, but no virulence was observed on the PlArg, Pl15, Pl17 and Pl18 genes. Using a discriminatory dose of 10 ug ai azoxystrobin/seed, no isolate approached infection levels found in inoculated, nontreated controls; therefore, the pathogen is considered sensitive to azoxystrobin in the greenhouse and azoxystrobin should still suppress downy mildew in the field.
The Effect of Substitution of Cytoplasmic Organelles on the Responses of Wheat to Foliar Pathogens
(North Dakota State University, 2016) Alhashel, Abdullah Fahad
Parastagonospora nodorum and Pyrenophora tritici-repentis are foliar pathogens of wheat, capable of causing up to 50% yield losses, and reduced grain quantity and quality, by infecting wheat leaves and kernels. The most economical means of disease control has been through the introduction of nuclear resistance genes. Changes in wheat’s nuclear-cytoplasmic (NC) interactions by the introduction of alien cytoplasms, can affect disease resistance. In this study, we investigated 32 alloplasmic lines derived from wheat cultivars Selkirk, Chris, and 56-1 (durum), in response to isolates of P. nodorum, P. tritici-repentis, and four host-specific toxins produced by them. All alloplasmic lines showed no difference from their parental lines with regards to toxin sensitivity. With spore inoculations, alloplasmic lines, SSM0039, SSM0237, and SSM0241, containing either Aegilops bicornis or Ae. longissima cytoplasm, exhibited increased disease resistance, compared to their parental lines. Two lines were found to be resistant to multiple isolates or pathogens.
The Effect of Variable Seed-Borne Inoculum Load of Dickeya dianthicola on Performance and Infection of Field Grown Potatoes
(North Dakota State University, 2020) Larson, William Kalvin
Field experiments were conducted at Live Oak, Florida, and Rhodesdale, Maryland, to evaluate the effect of variable seed-borne inoculum load of Dickeya dianthicola on potato plant emergence, plant growth throughout the growing season, disease prevalence in the field throughout the growing season, yield and grade, and transmission of D. dianthicola to progeny tubers. No statistically significant differences in emergence, plant height, or disease incidence were observed at either location. Statistically significant differences were observed in yield at the Florida location; all inoculated treatments had significantly lower yield than the non-inoculated control. No significant differences in yield were observed among treatments at the Maryland location. No significant differences in grade were observed at the Florida location. Significant differences in one tuber profile category were observed at the Maryland location. No significant differences in transmission of D. dianthicola to progeny tubers were observed at the Florida and Maryland locations.
Effects of synonymous and nonsynonymous Cyp51 mutations on DMI resistance in Cercospora beticola
(North Dakota State University, 2024) Courneya, Isaac
Cercospora beticola is the most devastating foliar pathogen of sugar beet. This pathogen is primarily managed by the application of fungicides, including demethylation inhibitors (DMIs). Given the broad use of DMIs in managing Cercospora leaf spot, resistance has developed. Recently, five haplotypes of CbCyp51 have been correlated with DMI resistance. To improve our understanding of these haplotypes, this study has evaluated CbCyp51 expression across haplotypes with and without DMI exposure using RT-qPCR. Significant differences were found between haplotypes in control and difenoconazole groups, but the broader implications were unclear. This study also produced mutant C. beticola strains with replaced CbCyp51 haplotypes. DMI sensitivity was assessed, revealing dramatic changes in difenoconazole resistance. Most mutants exhibited elevated tetraconazole resistance, which was largely shown to be associated with the transformation process rather than haplotype exchange. Further studies involving the different haplotypes and mutants could improve our understanding of these DMI resistance associated mutations.
Efficacy of Seed Treatments and In-Furrow Fungicides for Management of Dry Bean Root Rot Caused by Rhizoctonia Solani and Fusarium Solani, and Field Pea Root Rot Caused by Fusarium Avenaceum and Fusarium Solani
(North Dakota State University, 2017) Tvedt, Chryseis Theresa
Dry bean and field pea root rots have resulted in substantial yield losses in North Dakota. Root rot symptoms range from small lesions to complete root destruction. Traditional management practices such as seed treatment fungicides and crop rotation have proven insufficient under high disease pressure. The objective of this research was to determine the efficacy of in-furrow fungicide applications for management of dry bean and field pea root rot under field and greenhouse conditions. Fungicides were applied in-furrow at planting on dry beans and field peas. In most trials, the inoculated/non-treated control displayed significantly higher levels of root rot than the non-inoculated/non-treated control. In-furrow fungicides generally reduced root rot severity, sometimes significantly over the seed treatment; however, the level of control varied among hosts and pathogens. The results of these studies indicate that the use of in-furrow fungicides, along with cultural practices, may improve the overall management of root rot.
Ellucidation of RPG4/RPG5-Mediated Resistance Against Wheat Stem Rust in Barley
(North Dakota State University, 2015) Wang, Xue
Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a major threat to barley and caused devastating reductions in yield and economic losses. The barley line Q21861 was identified as the best source of resistance to the potential threat posed by the highly virulent Pgt race TTKSK. Resistance to TTKSK was mapped to the telomeric region of chromosome 5HL, now designated as the rpg4-mediated resistance locus (RMRL). RMRL has been delimited into two tightly linked yet distinct loci, designated as RMRL1 and RMRL2. Three genes (HvRga1, Rpg5, and HvAdf3) were found at RMRL1 while gene(s) at RMRL2 remains unknown. BSMV-VIGS revealed that all three genes at RMRL1 are required for rpg4-mediated resistance, which follows the emerging theme of dual genetically linked NBS-LRR genes required for resistance. HvAdf3 may play an important role in controlling host-specific resistance as suggested by AtADF4 in the Arabidopsis-Pseudomonas syringae plant-microbe interaction model.
Evaluating Chemical Seed Treatments for Fusarium Root Rot Control in Dry Beans and Field Peas
(North Dakota State University, 2014) Hegde, Namratha Prakashchandra
This study evaluated commercially available seed treatment products for their ability to control Fusarium solani and F. avenaceum, causal agents of root rot in dry edible bean and field peas, respectively, through in-vitro, growth chamber and field trials. Disease severity was assessed using a 0 to 5 scale, and root health parameters were recorded. The in-vitro tests conducted were not considered good predictors of fungicide performance in growth chamber or field trials in case of dry beans for management of F. solani. In case of field peas, in-vitro and growth chamber studies provided consistent results and allowed the identification of fludioxonil, trifloxystrobin and pyraclostrobin as the most effective products to manage F. avenaceum. Overall, integration of chemical seed treatments along with cultural practices; crop varieties partially resistant to root rot, and drench application is necessary to effectively manage Fusarium root rot of dry beans and field peas in field conditions.

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