Undergraduate Research Theses

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https://hdl.handle.net/11299/203510

This collection holds undergraduate research theses from students in one of the CFANS majors. Currently it includes theses from students in Agro 4097W in the Plant Science major.

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    Investigating net blotch resistance in Hordeum jubatum
    (2019-08) Miller, Michael
    Net blotch (Pyrenophora teres f. teres) is a major disease of barley (Hordeum vulgare). Genetic resistance in cultivated barley is mainly found in one major region of the genome, suggesting that wild relatives should be investigated to enhance the diversity of resistance in the cultivated species . This study looked at net blotch resistance in Hordeum jubatum, a member of the tertiary genepool of barley. Over 300 accessions of H. jubatum collected from 108 sites in central North America were grown in a greenhouse and tested for their reaction to pathotype Pt_1351 of P. teres f. teres. Twenty-eight differential accessions of barley were also evaluated as controls. Nine days after inoculation, plants were scored for their infection responses (IRs) on a ten-point scale. IRs were generally low, but variation was observed. The H. jubatum accessions had a mean IR of 2.9 and a range of 1 to 6.5. H. vulgare controls had mean IR of 2.5 and a range of 1 to 6. No general trend was seen with respect to IR and geographic location. The disease scores of the H. vulgare controls generally did not match expectations based on previous studies, but average infection scores similar to that of the H. jubatum in this study was seen in other studies of net blotch infection in wild Hordeum species. The lack of a trend in disease score compared to geographic location suggests that factors heavily influenced by geographic location, such as rainfall and barley cultivation, are not responsible for variation in net blotch resistance. Future studies of net blotch resistance in H. jubatum would benefit from increased replication to better assess differences between individual accessions. The variation in net blotch resistance seen in this study suggests H. jubatum may be a source of novel resistance and warrants further study into net blotch resistance in H. jubatum.
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    Intraspecific Salt Tolerance Variation in Nicotiana tabacum Pollen Germination and Pollen Tube Growth
    (2019-08) Johnson, Nicholas
    Salt stress affects 20% of global cropland. Excessive salt inhibits pollen germination and pollen tube growth (PTG), two crucial aspects of angiosperm ontogenesis. Pollen tolerance to salt and how tolerances vary intraspecifically are important factors of the sexual reproduction and evolution of flowering plants. Additionally, pollen response to salt is an effective screening method for whole plant salt tolerance. While the general field of plant salt tolerance is well studied, little research has been done on intraspecific variation in salt effect on pollen germination and PTG. The objective of this study was to investigate the effect of super-optimal levels of sodium chloride (NaCl) on pollen germination and PTG in vitro in 11 diverse genotypes of Nicotiana tabacum. NaCl tolerance was evaluated in three concentrations in N. tabacum pollen tube growth medium (TPTGM), where tolerance was observed in terms of PTG and pollen germination. ‘Mpeskq’ is NaCl tolerant relative to 10 other genotypes of N. tabacum. ‘Mpsekq’ pollen germination percentage was reduced by 5.8% and PTG was reduced by 34.6% from control TPTGM to 50mM NaCl TPTGM treatments. ‘Aparecido’ was the least NaCl tolerant, with a reduction of 62.6% PTG and 93.5% pollen germination between these same treatments. A strong positive correlation between PTG NaCl tolerance and pollen germination NaCl tolerance was also discovered (r = 0.74, p-value = 7.54e^(-7)). These findings show there is genetic variation for NaCl tolerance among diverse genotypes of N. tabacum. Future research should confirm this work and identify the genes responsible for NaCl resistance among genotypes such as ‘Mpsekq’ for use in N. tabacum or other crops.