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Item Understanding resistance and transcriptional responses to potato virus Y infection in potato plants(Montana State University - Bozeman, College of Agriculture, 2021) Ross, Brian Thomas; Chairperson, Graduate Committee: Michelle Flenniken; Nina Zidack and Michelle L. Flenniken were co-authors of the article, 'Extreme resistance to viruses in potato and soybean' in the journal 'Frontiers in plant science' which is contained within this dissertation.; Nina Zidack and Michelle L. Flenniken were co-authors of the article, 'Transcriptional responses to potato virus Y infection in resistant and susceptible potato cultivars' submitted to the journal 'Cultivars' which is contained within this dissertation.The potato is one of the world's most important crops. Cultivation of potatoes occurs on every continent except Antarctica and in a wide variety of climates. Potatoes are susceptible to a multitude of pathogens that can decrease yield and market quality. Viruses are particularly problematic for potato growers, as most potato production involves the replanting of tubers grown the previous year. Because virus-infected potato plants can harbor virus in their tubers, these tubers can in turn be the source of infection in the next generation of plants. Strains of Potato virus Y are the most economically burdensome viruses for potato growers worldwide. In field settings, Potato virus Y is primarily transmitted to plant by aphids feeding on leaves, but PVY can also be transmitted mechanically through infected plant sap. The use of insecticides and the application of mineral oil to leaves can help limit aphid populations and prevent infection to an extent but are generally both less effective and more environmentally impactful than genetic antiviral resistance mechanisms. The incorporation of genes that provide durable resistance to Potato virus Y into commercial potatoes is a major focus of potato breeders. One form of resistance, called extreme resistance, is characterized by a lack of symptoms and little to no virus replication occurring at the site of infection, but the molecular mechanisms of this response are not well understood. A comprehensive analysis of the extreme resistance literature indicates that movement of the resistance protein from the cytoplasm to the nucleus of the cell directly after virus infection may be a key aspect of this immune response. The downstream, transcriptional aspects of the extreme resistance response are also not well understood. We analyzed the gene expression from a Potato virus Y-resistant potato variety, Payette Russet, and a commonly grown susceptible variety, Russet Burbank, at a series of time points after virus infection using RNA sequencing. Results of these analyses indicate that an immune response likely occurs in Payette Russet quickly after virus inoculation. These analyses also indicate that the virus-susceptible variety, Russet Burbank, exhibits changes in gene expression that are similar to other susceptible potato varieties during asymptomatic or tolerant infection. Furthering our understanding of the molecular mechanisms controlling resistance and severity of virus infections will help inform future breeding and genetic engineering efforts, which require detailed knowledge of the mechanisms of virus resistance.Item Evaluation of susceptibility to wheat streak mosaic virus among small grains and alternative hosts in the Great Plains(Montana State University - Bozeman, College of Agriculture, 2011) Ito, Dai; Chairperson, Graduate Committee: Mary Burrows.Wheat streak mosaic virus (WSMV), endemic in small grains production areas of the Great Plains, causes yield losses of wheat 2 to 5% annually. Yield loss in individual fields can reach 100%. Control relies on cultural practices to control the vector, the wheat curl mite (Aceria tosichella Keifer, WCM), and the use of resistant or tolerant varieties. WSMV and WCM depend on living tissue for survival and reproduction, including common grassy weeds. Little is known about the relative importance of these weeds as alternative hosts of WSMV. The purpose of these studies was to evaluate the risk of infection with WSMV in commonly grown wheat varieties and various grassy weed species, information useful to understanding WSMV epidemiology and control. Winter wheat, spring wheat and barley varieties in Montana were evaluated in the field by measuring the effect of fall vs. spring inoculation and variety on incidence, symptom severity, and yield components. Winter wheat varieties from five states, and spring wheat and barley varieties from Montana were tested for incidence and absorbance in greenhouse. Fall-inoculated winter wheat had less effect of WSMV inoculation compared to spring-inoculated winter wheat. Yields of spring wheat varieties were largely reduced by WSMV inoculation. There was no correlation between yield and incidence or symptom severity. In greenhouse studies, the highest incidence was observed in varieties from Idaho and Nebraska, whereas the highest relative absorbance was observed in varieties from Montana. In 2008 and 2009, surveys of common grassy weeds were conducted. Grass species from croplands in six states were selected and mechanically inoculated to determine the susceptibility to WSMV. Grassy weeds were also evaluated as a source of WSMV by measuring transmission efficiency with virulifeous WCM. Bromus tectorum was the most prevalent grassy weed and the most frequent viral host. Aegilops cylindrica, and Avena fatua had the highest incidence and relative absorbance. There were no differences in the susceptibility of grass species to WSMV by their state of origin. WCM transmission study indicated infected grass species had lower transmission efficiency than from infected wheat. These studies will benefit producers in Montana to assess their risk of WSMV based on variety selection and the presence of grassy weeds.