Call number: LD2668 .T4 1956 P41 / Master of Science

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.

Common bean (Phaseolus vulgaris) is the most important legume for direct human consumption. Common bean originated and was domesticated in the Americas but now is grown worldwide. As in the case of other crops, common bean can be infected with acute and persistent plant viruses. A modified dsRNA extraction method was developed and used in this study. The method was fast, economic, versatile, and required relatively small amounts of desiccated plant tissue. The method was successfully used to extract dsRNAs from plants infected with RNA plant viruses and to investigate the occurrence of two endornaviruses, Phaseolus vulgaris endornavirus 1 (PvEV1) and Phaseolus vulgaris endornavirus 2 (PvEV2), in breeding lines, cultivars, landraces, and wild genotypes of common bean from the two centers of common bean domestication: Mesoamerica and the Andes. The two endornaviruses were detected in many common bean genotypes of Mesoamerican origin but rarely in genotypes of Andean origin. A comparative study of morphological and physiological characteristics between two common bean lines of the cultivar Black Turtle Soup (BTS); one infected with PvEV1 and PvEV2 (BTS+) and the other endornavirus-free (BTS-) was conducted. Morphological differences between the two lines were not observed. However, the study revealed that common bean endornaviruses may promote seed germination, pod length, and carotenoid content. Nevertheless, endornaviruses were associated with lower chlorophyll content. When interactions studies were conducted between PvEV1 and PvEV2 and three acute viruses, synergistic effects were obtained. Quantitative RT-PCR results supported a synergism between PvEV1 and Sunn-hemp mosaic virus. More research should be conducted to determine the type of symbiotic interaction that exists between common bean and endornaviruses.

Excess nitrate-N concentration (>10 mg L-1) in drinking water can cause significant risk to human health. Also, at very low concentration (0.035-0.1 mg P L-1), phosphorus is considered as a pollutant due to its effects of promoting algal growth and eutrophication of surface waters. This thesis’ research was conducted at two different sites. The first study was conducted at Carman on a sandy loam soil with cropping system, perennial versus annual, as the main plot and manure nutrient management system, as the subplot to measure nitrate and phosphorus leaching from hog manures. The second field experiment, located northwest of the town of Carberry, Manitoba, was conducted on a loamy sand soil. A two year rotation was employed for the annual cropping systems with a randomized complete block design. Treatments included two rates of liquid hog manure (LH-5000, LH-2500), two rates of fertilizers (F5000, F2500) corresponding to the amount of available nitrogen in the two rates of hog manure a compost treatment (Com-2500) and a control for a total of six treatments. The results from Carman site showed that while a substantial amount of nitrate-nitrogen was lost from the annual plots (40 to 60 kg ha-1 in 2010 and 23 to 60 kg ha-1 in 2011), a negligible amounts of nitrate was lost from the perennial (< 1 kg ha-1). There was no evidence of significant downward movement of phosphorus below the top 15 cm soil layer in this study. However, repeated, annual application of manure at an N-based rate resulted in increased soil test P. In Carberry, total N leaching of fertilizer amended plots was greater than in plots that received manure. Based on the results, application of liquid hog manure at the rate of 2500 gallon ac-1 was economically and environmentally more desirable and is recommended. We applied the multi-layer water balance model, VSMB, to the data that we generated in the field to gain an understanding of how well the model will simulate the loss of water that we measured from the lysimeters. The simulation study showed that the VSMB model grossly underestimated the amount of leached water, possibly due to an overestimation of evapotranspiration. / October 2015

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