Doctor of Philosophy (PhD)
Plant Pathology and Crop Physiology
Development of resistant cultivars is the main control measure against sugarcane brown rust caused by Puccinia melanocephala. Durability is uncertain, since the pathogen possesses adaptive ability to overcome host plant resistance. A differential gene expression study utilizing suppressive subtraction hybridization was conducted to improve understanding of brown rust resistance mechanisms in sugarcane. The expression patterns of 11 unigenes representing biosynthetic pathways, defense-related genes, and signaling genes were analyzed in L 99-233, a cultivar exhibiting quantitative resistance, L 01-299, a resistant cultivar with the major resistance gene Bru1, and two susceptible cultivars, Ho 95-988 and L 09-125, at 24 h, 48 h, 72 h, and 1 week after inoculation with P. melanocephala using (semi)quantitative RT-PCR. All genes analyzed for their expression showed message accumulation upon infection in susceptible and resistant cultivars, but the maintenance of high amounts of mRNAs of the genes for a prolonged time period appeared to be the most important factor contributing to brown rust resistance. Differences in the time-course of gene expression were detected between L 01-299 and L 99-233 suggesting variable mechanisms for resistance between the cultivars. Molecular markers were used to screen the World Collection of Sugarcane and Related Grasses (WCSRG) for Bru1 to determine its distribution and frequency in Saccharum species and related genera. A total of 1,282 clones were screened. Bru1 was distributed across the Saccharum complex, but the frequency varied among species. Bru1was more prevalent in S. robustum clones (59.1%), whereas it occurred in low frequency and exhibited the highest level of variability in clones of S. spontaneum (18.8%). Bru1 frequency was highest in the two secondary cultivated species, S. barberi (79.3%) and S. sinense (71.8%). The frequency of Bru1 detection was 26.4% and 21.0% for S. officinarum and interspecific hybrid clones, respectively. The characterization of the WCSRG for Bru1 distribution and prevalence will complement efforts to characterize diversity in the Saccharum complex for the expected expanded use of marker-assisted selection in the future. Selection for quantitative resistance in combination with Bru1 could allow breeding programs to develop sugarcane cultivars with effective and durable resistance against brown rust.
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Avellaneda Barbosa, Mavir Carolina, "Identification of Genes Associated with Resistance to Brown Rust in Sugarcane and Prevalence of One Major Gene" (2016). LSU Doctoral Dissertations. 3645.
Hoy, Jeffrey W.