Plant Sciences Masters Theses

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Browsing Plant Sciences Masters Theses by browse.metadata.program "Plant Pathology"

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    Assessment of Bacterial Blight Pathogens Prevalent on Dry Bean and Identification of Sources of Resistance to Rhizoctonia Root Rot in North Dakota
    (North Dakota State University, 2011) Yen-Wei, Chang
    Bacterial blights and root rots are two major diseases affecting dry edible bean (Phaseolus vulgaris L.) production in North Dakota and Minnesota (Venette and Lamey 1998). Bacterial blights of dry bean are commonly caused by three bacterial pathogens, namely Pseudomonas syringae pv. phaseolicola (Psp), Pseudomonas syringae pv. syringae (Pss) and Xanthomonas axonopodis pv. phaseoli (Xap), which can appear either together or independently under natural conditions. The bacterial portion of this study involved ascertaining the extent of incidence of bacterial blight in the major dry bean production areas of ND through surveys, determining the prevalence of Psp and Pss and screening a collection of commercial varieties from different market classes for resistance to these two bacterial pathogens. In this study, more than 50% of the fields surveyed in all the major dry bean producing counties, including Grand Forks, Pembina, Traill and Walsh from year 2008 to 2010, were found to have been affected by bacterial blight. Among the bacterial diseases, bacterial brown spot (caused by Pss) appeared to be the most prevalent. Representative isolates for both Psp and Pss randomly selected from the survey were used for pathogenicity tests and confirmed to be pathogenic. Race typing of the Psp isolates confirmed the presence of the races 6 and 8 in the field samples with race 6 being the most common. Susceptibility of the 11 varieties used in this study was also variable. Difference in aggressiveness was observed among the Psp isolates.
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    Association Mapping to Identify Sclerotinia sclerotiorum Genomic Regions Affecting Aggressiveness of Lesion Formation on Sunflower Stems
    (North Dakota State University, 2019) Belay, Kassaye Hussen
    Sclerotinia sclerotiorum is one of the most destructive pathogens of sunflower in the United States and worldwide. Distinctive symptoms include mid-stalk rot, basal stalk rot and head rot from subsequent infection of the sunflower head. This fungal pathogen has a remarkably broad host range of over 400 dicot plants. However, little is currently known about the virulence strategies that allow S. sclerotiorum to successfully infect a wide range of plant hosts. The goal of our project was to identify S. sclerotiorum virulence determinants and effectors that contribute to disease development on sunflower. We evaluated a diverse collection of 232 S. sclerotiorum isolates for aggressiveness of mid-stalk lesion formation on two sunflower inbred lines. In addition, we performed genotyping-by-sequencing on 191 isolates to identify genetic markers for genome-wide association mapping to identify candidate genes associated with aggressiveness. A total of eight loci associated with variation in aggressiveness were identified.
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    Developing a Blackleg Management Package for North Dakota
    (North Dakota State University, 2019) Upadhaya, Sudha G C
    Blackleg, caused by Leptosphaeria maculans, inflicts greatest canola yield losses when plants are infected before reaching the six-leaf growth stage. Studies were conducted to model pseudothecia maturation and ascospore dispersal to help growers make timely foliar fungicide applications. Pseudothecia maturation occurred mostly during the second half of June or in July in 2017 and 2018 in North Dakota and ascospores concentrations peaked during mid to late June in both years. A logistic regression model developed using temperature and relative humidity predicted the maturation of pseudothecia and ascospore dispersal with approximately 74% and 70% accuracy respectively. In addition, trials to evaluate the efficacy of five seed treatment fungicides were conducted under greenhouse and field conditions. All treatments reduced (P = 0.05) disease severity on seedlings in greenhouse trials, but not in field trials. Seed treatments, while a valuable tool, should not be used as the only means to manage blackleg.
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    Exploring Cover Crops for Managing Plant-Parasitic Nematodes Heterodera Glycines and Pratylenchus Penetrans
    (North Dakota State University, 2022) Neupane, Kamal
    Three studies were conducted to assess the effects of cover crops on plant-parasitic nematodes (PPNs) of potato and soybean. The first study investigated the hosting and population reduction abilities of 25 cover crops to Pratylenchus penetrans and found alfalfa (Bullseye) to reduce the initial population densities consistently. The second study tested the population reduction abilities of ten cover crops to two soybean cyst nematode (SCN; Heterodera glycines) populations in the microplot. Sunnhemp (cultivar not specified) was the most effective to reduce both SCN populations. The third study evaluated ten cover crops in a growth chamber for their impacts on hatching and root penetration of SCN and their potential as trap crops. Faba bean (Petite) showed the greatest potential to act as a trap crop for SCN, based on its effect on hatching and root penetration by SCN. These results help select suitable cover crops to manage PPNs in infested fields.