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Title:Characterizing maize resistance to Clavibacter nebraskensis
Author(s):Mullens, Alexander
Advisor(s):Jamann, Tiffany M
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:M.S.
Genre:Thesis
Subject(s):Clavibacter nebraskensis
host resistance
GF
Abstract:Clavibacter nebraskensis (Cn) causes Goss’s bacterial wilt and leaf blight, a major disease of maize. Infected crop residue is the primary inoculum source and infection can occur via wounds or natural openings, such as stomata or hydathodes. The use of resistant hybrids is the primary control method for this disease. In this study, colonization and movement patterns of Cn during infection were examined using green fluorescent protein (GFP)-labeled bacterial strains. We successfully introduced a plasmid to Cn via electroporation, which resulted in GFP expression. Fluorescence microscopy revealed that the bacteria initially colonize the xylem, and subsequently the mesophyll, which creates the freckles that are characteristic of the disease. In the absence of wounding, the bacteria colonized leaf tissue via the hydathodes when guttation droplets were present. Stomatal penetration was not observed under natural conditions. Bacteria forcibly infiltrated into the mesophyll did not cause typical disease symptoms and could not enter the vasculature. The resistant maize lines exhibited decreased bacterial spread in the vasculature and the mesophyll. Based on this information we identified phenotypes that allowed us to measure different components of Cn’s penetration and colonization of maize. We used these phenotypes to quantify the mechanisms of resistance in 20 diverse inbred lines. We measured six different phenotypes. Significant differences were observed for all the phenotypes among the evaluated lines. We found that some lines were differentially susceptible depending on whether a wounding or non-wounding inoculation method was used, indicating that hydathode-mediated resistance may exist in maize. Correlation coefficients between the phenotypes are consistent with the idea that resistance to Cn involves both vascular and non-vascular components. Additional observations made using the (GFP)-labeled strains provided evidence for hydathode-mediated resistance, resistance involving localized cell death similar to a hypersensitive response and vascular defense responses that resulted in the suppression of bacterial growth in the veins. With these tools to examine Cn’s colonization and movement we can gain insights into the pathogenesis process which could form the basis for improved Goss’s wilt management through host resistance.
Issue Date:2020-05-11
Type:Thesis
URI:http://hdl.handle.net/2142/108315
Rights Information:Copyright 2020 Alexander Mullens
Date Available in IDEALS:2020-08-27
Date Deposited:2020-05


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