Theses and Dissertations at Montana State University (MSU)
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Item Aphanomyces euteiches spatial distribution, host studies, and characterization in Montana(Montana State University - Bozeman, College of Agriculture, 2022) Murphy, Carmen Yvette; Chairperson, Graduate Committee: Mary BurrowsGrowing pulse crops in Montana has been inhibited by biotic constraints to production, including a complex of pathogens causing root rot. Aphanomyces root rot, caused by the soilborne oomycete, Aphanomyces euteiches, causes plant stunting and yellowing, root browning and constriction, and reduces yield in dry pea and lentil in the state. Twelve fields with a history of pulse root rot were sampled in northeast Montana with three 100 m entrance transects and one 50 m transect at a low spot or problem area. Soil from each 10 m quadrat within transects was assessed for root rot using a greenhouse bioassay with a susceptible dry pea variety, and with PCR. Samples were also analyzed for soil properties and nutrients. Distribution of the pathogen was sporadic in most fields, except for fields that had been growing pulses in a consistent rotation, where root rot severity was high and consistent. Soil pH, organic matter, potassium, and sulfur concentration were correlated with Aphanomyces root rot, and isolates varied in their response to acidic pH in vitro. Using a highly virulent A. euteiches isolate, greenhouse trials were conducted to assess the pathogen load of inoculated soil after growing host and non-host plant species, measured with a bioassay. Greenhouse pots were inoculated with 500 oospores per gram prior to planting plant treatments. Growing host plants resulted in higher root rot severity on dry pea bait plants compared to non-host plant treatments. When five cycles of plants were grown in greenhouse pots inoculated with A. euteiches, using five 'rotation' treatments, one treatment with three consecutive rounds of non-host plants reduced the disease severity score in one trial repetition compared to treatments with less than three successive rounds growing a non-host. This research indicates that sampling strategies for Aphanomyces root rot requires multiple sampling locations within a field to enhance the probability of detection, and that crop rotation is an important tool for management of pathogen load in the soil.Item The characterization of fungicide resistance, population structure, and aggressiveness of fungal species associated with ascochyta blight of pulse crops in Montana(Montana State University - Bozeman, College of Agriculture, 2019) Owati, Ayodeji Stephen; Chairperson, Graduate Committee: Mary Burrows and Bright Agindotan (co-chair); Bright Agindotan, Julie Pasche and Mary Burrows were co-authors of the article, 'The detection and characterization of QOI-resistant Didymella rabiei causing ascochyta blight of chickpea in Montana' in the journal 'Frontiers in plant science' which is contained within this dissertation.; Bright Agindotan and Mary Burrows were co-authors of the article, 'First microsatellite markers developed and applied for the genetic diversity study and population structure of Didymella pisi associated with ascochyta blight of dry pea in Montana' in the journal 'Fungal biology' which is contained within this dissertation.; Bright Agindotan and Mary Burrows were co-authors of the article, 'Characterization and detection of fungal species associated with ascochyta blight of dry pea in Montana' submitted to the journal 'Plant disease' which is contained within this dissertation.; Bright Agindotan and Mary Burrows were co-authors of the article, 'The development and application of real-time and convention SSR-PCR assays for rapid and sensitive detection of Didymella pisi associated with ascochyta blight of dry pea' submitted to the journal 'Plant disease' which is contained within this dissertation.Ascochyta blight (AB) of pulse crops causes yield loss in Montana, where 1.24 million acres were planted to pulses in 2018. Pyraclostrobin and azoxystrobin, quinone outside inhibitor (QoI) fungicides, have been the choice of farmers for the management of AB in pulses. QoI-fungicide-resistant Didymella rabiei isolates were found in one chickpea seed lot each received from Daniels, McCone and Valley Counties, MT, from seed produced in 2015 and 2016. Multiple alignment analysis of amino acid sequences showed a mutation that replaced the codon for amino acid 143 from GGT to GCT, introducing an amino acid change from glycine to alanine (G143A), which is reported to be associated with QoI resistance. Under greenhouse conditions, disease severity was significantly higher on pyraclostrobin-treated chickpea plants inoculated with QoI-resistant isolates of D. rabiei (QoI-R) than sensitive isolates (QoI-S) (p-value = 0.001). D. rabiei-specific PCR primer pair and probes were developed to discriminate QoI-R and QoI-S isolates. In North America, AB of dry pea is caused by a complex of fungal pathogens (Didymella pisi, Peyronellaea pinodes, and Peyronellaea pinodella). D. pisi is the predominant causal pathogen of AB of dry pea in Montana resulting in yield losses. Thirty-three microsatellite markers (SSR) were developed and used to analyze the genetic diversity and population structure of 205 D. pisi isolates from four geographical regions of Montana. Unweighted Neighbor-joining, principal coordinate, and population structure analyses grouped these 205 isolates into two major sub-groups. The clusters did not match the geographic origin of the isolates. Analysis of molecular variance showed 85% of the total variation within populations and only 15% among populations. There was moderate genetic variation in the total populations (PhiPT = 0.153). Recently, a shift in pathogen composition has been observed in Montana from D. pisi to P. pinodes and P. pinodella. Also, a Phoma sp. was found associated with AB contaminated dry pea seeds and included in this study. Mycelial growth and sporulation were evaluated at different temperatures. Also, the pathogenicity of Phoma sp. and the difference in aggressiveness among the fungal pathogens was evaluated. At all temperatures, Phoma sp. had the highest growth rate (p-value = < 0.001) and produced more spores than the other species (p-value = < 0.001). P. pinodes caused greater disease severity than the other species when inoculated on pea plants (cv. Carousel, p-value < or = 0.001). The Phoma sp. was not pathogenic. Peameal agar was used to visually discriminate between fungal species. Diagnosis of AB of dry pea is challenging because of the complex of pathogens involved. Also, they have slow growth rate and different morphotypes. Currently, there are no PCR-based assays developed for D. pisi or any of the fungal pathogens associated with the AB complex of dry pea. D. pisi specific SYBR green SSR-qPCR and conventional SSR-PCR assays were developed for rapid detection and quantification of D. pisi both in-planta and in-vitro.Item Phylogenetic systematics of Strophostyles (Fabaceae)(Montana State University - Bozeman, College of Agriculture, 2003) Riley-Hulting, Erin ThaisItem Phosphorus uptake from insoluble soil sources by five forage legumes, winter wheat, and buckwheat(Montana State University - Bozeman, College of Agriculture, 1979) Jacques, Robert Mark