Plant Pathology Masters Theses

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Evaluation of fungicide sensitivity and forms of resistance of selected Diaporthe species in soybean (Glycine max L.)
(North Dakota State University, 2024) Mankara Sureshbabu, Bijula
In U.S, Diaporthe species caused yield losses of 0.2 million metric tons in soybean in 2022. Quinone outside inhibitor fungicides carry high risk of fungicide resistance and may use for managing Diaporthe. In this study, isolates of D.aspalathi, D.caulivora and D.longicolla from 16 U.S. states were tested for their sensitivity to azoxystrobin. Significant effect of isolates (P<0.05) was observed on effective concentration at which mycelial growth was inhibited by 50% (EC50). The results showed the presence of sensitive Diaporthe isolates in soybean to azoxystrobin. Moreover, resistance to stem and seed infection by D.longicolla was evaluated in 39 soybean accessions. Significant effect of genotypes was observed on disease severity of stem and seed infection (P<0.05). Correlation between disease severity of stem and seed infection was non-significant. Results indicate defense mechanism against D.longicolla during stem and seed infection may differ. These findings indicate need to determine alternative fungicide chemistries and develop Diaporthe-resistant soybean varieties.
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.
Managing Sclerotinia sclerotiorum: an emerging threat to the sugar beet industry
(North Dakota State University, 2024) Aderoju, Mayowa
Recent studies have reported S. sclerotiorum (Lib.) de Bary as an emerging pathogen of sugar beet (Beta vulgaris L.) causing leaf blight, seedling damping-off and root necrosis, becoming a fundamental production problem in the Red River Valley of North Dakota and Minnesota. The continuous spread of this pathogen's damaging impact across sugar beet-producing states necessitates proactive management measures to reduce the risk of potential outbreaks. This study aimed to (1) assess inoculation methods for sugar beet reaction to S. sclerotiorum, varietal response and cross-infectivity, and (2) evaluate fungicide efficacy against Sclerotinia diseases in three sugar beet varieties. Disease evaluation was measured as lesion size. Results from this study indicated that colonized barley inoculum was particularly effective in causing leaf blight on sugar beet plants (P= 0.05). Crystal M837 variety showed reduced susceptibility to Sclerotinia leaf blight. ACH 166 and Beta 7029 were moderately susceptible to leaf blight, but for root infection, they showed reduced susceptibility which was significant at all stages during the fungicide efficacy study (P= 0.05). Proline and Priaxor provided the most effective control against Sclerotinia leaf blight and root necrosis in sugar beet (P= 0.05). These findings offer critical insights into sugar beet variety and fungicide selection for effective control of S. sclerotiorum. Also, vital information about the cross-infectivity status of major host crops (soybean, sunflower and canola) provides valuable information for crop rotation decisions towards mitigating losses caused by S. sclerotiorum. This study gives a first look into managing S. sclerotiorum, an emerging pathogen of sugar beet and a potential threat to the sugar beet industry.
The Impact of Plant Age, Fungicide Application Methodology and Timing, and Depth of Soil Inoculation on Infection by Rhizoctonia solani on Sugarbeet.
(North Dakota State University, 2010) Pooran-DeSouza, Scmwattie
Rhizoctonia root rot caused by Rhizoctonia solani (Kuhn), is the most important problem faced by sugarbeet (Beta vulgaris L.) grm.vers in North Dakota and Minnesota. Research was conducted that may be used to manage the disease. Six cultivars from 2 to 8- leaf stage were evaluated for their ability to withstand infection after soil inoculation by R. solani AG 2-2 IIIB. All leaf stages of the cultivars evaluated were susceptible to R. solani. Sugarbeet plants at the 2-leaf stages were most susceptible and had significantly higher root rot severity than plants at the 4, 6 and 8-leaf stages. Cultivars Crystal 454 and Hillshog 3035 had the lowest root rot severity of the cultivars evaluated, but root rot severity was still greater than 50%. The cultural practice of planting early in soils when the temperature is about 10°C at the 10 cm depth may result in plants being older and more tolerant by the time the pathogen becomes infective at warmer soil temperatures. However, the fact that all plant stages were susceptible to R. solani may require additional protective measures in highly infested fields with a knovm history of severe Rhizoctonia root rot. During greenhouse research, it was observed that azoxystrobin fungicide applied as a hypocotyl drench provided excellent control of Rhizoctonia root rot. It is recommended that growers use a foliar banded application of azoxystrobin at the 4-leaf stage to control Rhizoctonia root rot. Research was conducted to compare and evaluate the effect of foliar band and hypocotyl drench applications of azoxystrobin to control R. solani. The study showed that foliar banded and hypocotyl drench applications of azoxystrobin provided significantly similar disease control under conditions that were ideal for disease development However, disease from plants with a hypocotyl drench application was not significantly different than the non-inoculated control suggesting that further testing should be done to determine the utility of this application methodology in field conditions. Research was conducted to determine the best time to apply azoxystrobin fungicide for effective R. solani control relative to timing of soil inoculation. Sugarbeet hypocotyls were drenched at the 4-leaf stage at 0, 7, 14, 21, and 28 days pre-inoculation and at 0, 3, 10, 14, and 21 days post-inoculation. Azoxystrobin applications prior to inoculation resulted in significantly lower root rot compared to fungicide applications at post inoculation. Among the post inoculation applications, treatments where the fungicide was applied within 2 hours provided the best disease control. Fungicide application at pre-inoculation provided effective control at all timings evaluated: This research reinforces the need for azoxystrobin application before infection to control the disease in field conditions. The depth at which R. solani caused root rot infection of sugarbeet was studied after burying R. solani AG 2-2 IIIB inoculurn at depths of 2.54, 7 .62, and 12. 7 cm. R. solani AG 2-2 IIIB infections occurred at all depths of inoculation. However, inoculum buried at 2.54 cm depth had significantly higher root rot severity than inoculum buried deeper. Root rot symptoms were prevalent on the upper portion of the sugarbeet root just below the soil line irrespective of the depth of inoculurn placement. This suggests that the upper part of the root below the soil line is most vulnerable to R. solani infection. Consequently, in the soil fungicide application should target the root area just below the soil line for effective disease control.
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.
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.
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.
Identification and Characterization of Novel Cercospora beticola Necrosis-Inducing Effectors
(North Dakota State University, 2021) Hamilton, Olivia Grace
Cercospora beticola is a hemibiotrophic fungus responsible for Cercospora leaf spot disease of sugar beet (Beta vulgaris). Plant pathogens such as C. beticola utilize “effector” molecules to aid in disease establishment. Effectors are generally small, secreted molecules that contribute to pathogen virulence. A culture filtrate infiltration study was conducted to identify potential effector molecules secreted by C. beticola. A variety of fungal growth conditions were pursued, one of which resulted in a necrotic phenotype when the culture filtrate was infiltrated into sugar beet leaves. The culture filtrate was fractioned using ion-exchange chromatography. Fractions were infiltrated to identify the protein responsible for necrosis. Five candidate necrosis-inducing effector proteins were identified through mass spectrometry analysis. Targeted gene disruption of these candidates and subsequent virulence assays revealed an increased virulence for Δ05663 strains compared to the inoculated wild-type. Full characterization of this candidate effector will shed light on the C. beticola-sugar beet interaction.
Improving Disease Management in Field Pea and Durum Wheat in the MonDak Region
(North Dakota State University, 2021) Gargouri-Jbir, Taheni
Results from wilt pathogenicity and race evaluations for 25 North Dakota Fusarium oxysporum f.sp. pisi (Fop) isolates conducted in the greenhouse indicated all Fop races exist in North Dakota. Race 2 isolates were more frequently recovered from plants with root rot symptoms. Root rot assays also conducted in the greenhouse demonstrated that most Fop isolates were as aggressive as F. solani and F. avenaceum based on increased root disease severity. Results from field experiments conducted in 4 sites in the MonDak region between 2017 and 2019 evaluating the effect of three planting dates and six durum varieties with differing levels of susceptibility to leaf spot and Fusarium Head Blight (FHB) indicated that early planting maximized yield and influenced ergot incidence. Although planting date did not affect late leaf spot and DON, choosing less susceptible varieties to fungal leaf spot and FHB reduced late fungal leaf spot and DON, respectively.
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.
Resistance Screening and QTL Mapping in Wheat and Triticale Against Root-Lesion Nematode
(North Dakota State University, 2020) Singh, Gurminder
Root-lesion nematode (RLN, Pratylenchus neglectus) invades the roots of wheat and causes yield losses throughout the world. Genetic resistance is the most economical and effective means to manage RLNs. The objective of this study were to identify source of resistance to RLN in a small collection of wheat germplasm and to map quantitative trait loci (QTL) associated with RLN resistance in two; one wheat and one triticale recombinant inbred line (RIL) populations. Out of wheat lines, three were resistant, including hard red spring wheat cultivars Brennan, SY Ingmar, and SY Soren. A number of genomic regions in wheat and rye were identified as QTL for RLN resistance. My research provides a better understanding of the genetic basis of P. neglectus resistance and important tools for RLN resistance breeding.
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.
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.
Plant-Parasitic Nematodes on Sugarbeet in North Dakota and Minnesota
(North Dakota State University, 2019) KC, Ashmit
Field surveys were conducted in the Red River Valley (RRV) of North Dakota and Minnesota during 2016 and 2017 to determine the incidence, abundance, and distribution of plant-parasitic nematodes (PPNs) on sugarbeet. Seventy-two and 65 % of the fields surveyed were positive for PPNs in 2016 and 2017, respectively. The major genera of PPNs identified from sugarbeet production fields were Heterodera, Helicotylenchus, Tylenchorhynchus, Paratylenchus, Pratylenchus, Paratrichodorus, Hoplolaimus, and Xiphinema. Eight of PPNs were identified at the species level using species-specific PCR assays, and sequencing of the ribosomal rDNA gene. Stubby-root nematode, Paratrichodorus allius, is one of the important nematode pests for sugarbeet production worldwide. An experiment was conducted to determine the host status of sugarbeet and their rotational crops for P. allius under greenhouse conditions. The results from two experiments indicated sugarbeet and most rotational crops support the reproduction of P. allius.
Inoculation and Spread of Dickeya in Potatoes
(North Dakota State University, 2019) Greiner, Blake William
Field experiments were conducted in two different growing environments to evaluate the spread and movement of Dickeya dadantii. A procedure to inoculate seed potatoes with Dickeya dadantii was developed to use during this study. Spread of Dickeya dadantii from inoculated potato seed to healthy potato seed during the handling, cutting and planting procedures was not detected at either location. Spread of Dickeya dadantii from inoculated seed to surrounding progeny tubers in the field was documented in both locations. In Florida, 33% of progeny tubers tested positive for Dickeya using PCR, and in North Dakota, 13% of the progeny tubers tested positive. Stunting was observed in plants grown from Dickeya dadantii inoculated seed tubers in North Dakota, but not in Florida. These results indicate that Dickeya dadantii may spread during the seed handling and cutting processes and can spread in the field from infected seed tubers to progeny tubers.
Screening of Germplasm Accessions from the Brassica Species for Resistance against PG3 and PG4 Isolates of Blackleg
(North Dakota State University, 2011) Marino, Dante
Blackleg is a disease of canola and rapeseed cultivars that is caused by the fungus Leptosphaeria maculans (Desm.) Ces. & de Not., and it is by far the most destructive pathogen of canola in North America. In recent years, blackleg strains belonging to pathogenicity groups (PG) 3 and 4 have been discovered in North Dakota. Recent outbreaks of the disease have added a sense of urgency to characterize the risk these new strains represent for the canola industry and to identify sources of resistance against them. Thus, the objectives of this study were to screen germplasm collections of Brassica rapa, B. napus. and B. juncea for their reaction to PG3 and PG4 and to evaluate the reaction of a sample of currently used canola commercial cultivars grown in North Dakota to PG3 and PG4 as means to estimate the risk these new strains represent. All canola germplasm and commercial cultivars were evaluated in replicated trials in greenhouse conditions using cotyledon bioassays. In 2009 and 2010, the effect of these strains, using five inoculation sequences, on the reaction of canola seedlings was also evaluated. Field trials were not conducted because of the limited geographical distribution of the new strains. No adequate sources of resistance were identified among the 277 B. rapa and 130 B. napus accessions evaluated; however, 22 of the 406 accessions of Brassicajuncea evaluated were considered to have moderate levels of resistance. B. juncea seedlings that survived these inoculations were self-pollinated and their progeny (F1) were also screened. As before, surviving seedlings were self-pollinated. These F2 seeds are the elite materials that could be used in future breeding programs. The complementary study evaluating the role of sequence inoculations in reaction of canola seedlings to blackleg indicated that an increased susceptibility to PG3 occurred when seedlings were first inoculated with PG4; however, reaction to PG4 was not enhanced by a prior inoculation with PG3. All 75 commercial cultivars evaluated were susceptible to PG3 and PG4, indicating that the risk these new strains represent to the canola industry of the region is serious. Further, when a subsample of 16 cultivars were challenged with PG2, they were either resistant or moderately resistant, suggesting the ratings the industry are using relate to reaction of those cultivars to PG2 but not to the new strains; thus, growers should use caution when using these ratings while deciding on which cultivars to plant.
Plant-Parasitic Nematodes in Field Pea and Potato and their Effect on Plant Growth and Yield
(North Dakota State University, 2018) Upadhaya, Arjun
In this study, surveys were conducted in pea and potato fields in North Dakota and Central Minnesota to investigate the incidence and abundance of plant-parasitic nematodes in these fields. Moreover, the effect of the pin nematode, Paratylenchus nanus, on plant growth and yield of six field pea cultivars was determined under greenhouse conditions. Similarly, the influence of lesion nematode, Pratylenchus penetrans, and wilt fungi, Fusarium oxysporum alone and together on growth and yield of potato cultivar ‘Red Norland’, was evaluated in microplots under field conditions. The results indicate Paratylenchus spp. and Pratylenchus spp. are the most frequent nematodes, respectively, in pea and potato fields. Pin nematodes reproduced on field pea cultivars and caused up to 37% reduction in plant height and 40% reduction in yield. Additionally, both P. penetrans and F. oxysporum alone, and together had significant negative effect on growth and yield of potato.
Expression Analysis of the Expanded Cercosporin Gene Cluster in Cercospora beticola
(North Dakota State University, 2018) Stott, Karina
Cercospora leaf spot is an economically devastating disease of sugar beet caused by the fungus Cercospora beticola. It has been demonstrated recently that the C. beticola CTB cluster is larger than previously recognized and includes novel genes involved in cercosporin biosynthesis and a partial duplication of the CTB cluster. Several genes in the C. nicotianae CTB cluster are known to be regulated by ‘feedback’ transcriptional inhibition. Expression analysis was conducted in wild type (WT) and CTB mutant backgrounds to determine if feedback inhibition occurs in C. beticola. My research showed that the transcription factor CTB8 which regulates the CTB cluster expression in C. nicotianae also regulates gene expression in the C. beticola CTB cluster. Expression analysis has shown that feedback inhibition occurs within some of the expanded CTB cluster genes. The partial duplication of the CTB cluster was not found to be light activated or subject to feedback inhibition.
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.
Identification of Quantitative Trait Loci for Resistance to Tan Spot in Durum Wheat
(North Dakota State University, 2018) Galagedara, Nelomie Nayanathara
Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is a major foliar disease on wheat. The pathosystem involves three pairs of necrotrophic effector (NE) and host sensitivity (S) gene interactions, namely Ptr ToxA-Tsn1, Ptr ToxB-Tsc2 and Ptr ToxC-Tsc1. Additionally, genetic factors conferring race-nonspecific resistance have been identified. The objectives of this study were to map tan spot resistance QTL and investigate the role of NE-S interactions in disease in durum using association and bi-parental mapping. Evaluation of a worldwide collection of durum accessions allowed identifying highly resistant nineteen lines to multiple Ptr races. Association mapping revealed genomic regions on chromosomes 1A, 2B and 3B significantly associated with resistance to tan spot, which likely correspond to Tsc1, Tsc2 and racenonspecific resistance. Using a bi-parental population derived from Ben and PI 41025, we found that ToxA-Tsn1 interaction plays no significant role in disease, instead a major race-nonspecific QTL on chromosome 5A was identified.

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