Tubers of Russet Burbank were surface disinfested and 3 mm diameter by 3 mm deep wounds were made with cork borer. The holes were inoculated with 20muL of 104 macroconidia/ml suspension of (Fusarium sambucinum) or 20muL of 104 sporangia/ml suspension (Pythium ultimum) and incubated under mist. For infection studies, the inoculated tubers were exposed to 0--48 h of mist at 4--20ºC, dried and stored at 16ºC and 95% RH in growth chamber with forced air for 15 d (F. sambucinum), whereas stored at 12ºC and 95% RH for 30 d (P. ultimum). For lesion expansion studies tubers exposed to 24 h wet at 16ºC were stored in growth chambers at 4, 8, 12, and 16ºC for 15--90 d. At the end of storage tubers were cut and the volume of diseased area was measured. Models explained 94.2% of the variation in infection and 99.7% in lesion expansion for F. sambucinum . Whereas, models explained 96.7% of the variation in infection and 99.6% lesion expansion for P. ultimum. (Abstract shortened by UMI.)

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 98-110). / ix, 110 leaves, bound ill. (some col.) 29 cm

Thesis (PhD)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: David K. Weaver. Includes bibliographical references.

Thesis (Ph.D.(Plant Pathology)--University of Pretoria, 2006. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Three independent studies were conducted for spot blotch (Bipolaris sorokiniana), Fusarium head blight (FHB) (Fusarium graminearum), and root rot diseases (Fusarium species and B. sorokiniana). Histopathology of compatible and incompatible interactions between different pathotypes of B. sorokiniana and different genotypes of barley was examined with red fluorescent protein-tagged fungal isolates. The fungus penetrated the host cell wall and developed multicellular globular infection hyphae (IH) in the lumen of epidermal cells, but infected epidermal cells appeared to be alive till 16 hours post-inoculation (HPI). In the susceptible plants, the tip of IH was found to grow ahead of the dead tissue and invade the surrounding live mesophyll cells, whereas growth of IH in the resistant plants was restricted to the dead tissue after 20 HPI. The amount of H2O2 accumulation and the fungal biomass were also significantly higher in the susceptible hosts than in the resistant hosts. To map resistance to FHB, two populations consisting 130 doubled haploid lines from the cross Grandin × PI277012 and 237 recombinant inbred lines from the cross Bobwhite × ND2710 were phenotyped and genotyped. QTL for Type I resistance were identified on chromosomes 1A, 2B, 4B, 5B and 6B in the GP population. These QTL explained 10.7-19 % of the total phenotypic variation. With the BN population, QTL for Type I resistance were identified on chromosomes 2A, 5A and 6B, explaining 6.2-13.7% of the total phenotypic variation. To assess the prevalence, incidence and severity of wheat crown rot (CR) and common root rot (CRR) in ND, wheat root samples were collected from fields across the state in 2012, 2013, and 2014. Fungal isolations indicated that B. sorokiniana was most frequently recovered in all sampled years. Seedling tests on ten spring wheat lines showed that Glenn was the least susceptible while Steele-ND was the most susceptible to one F. culmorum isolate and one B. sorokiniana isolate tested. Evaluation of 20 spring wheat genotypes for reaction to CRR at the adult plant stage showed that Freyr and RB07 were more resistant while Len and Briggs were more susceptible to CRR compared to other wheat genotypes evaluated. / North Dakota Wheat Commission, / Minnesota Wheat Research and Promotion Council / ND State Board of Agricultural Research and Education / Triticeae-CAP project (2011-68002-30029) of the US Department of Agriculture National Institute of Food and Agriculture / U.S. Wheat and Barley Scab Initiative (USWBSI)

Fusarium root rot is one of the most important diseases of pulse crops, with numerous Fusarium spp. comprising the disease complex. Fusarium solani and F. avenaceum have been reported to be major pathogens in the pea root rot complex, and all commonly grown varieties are susceptible. Greenhouse methods to evaluate peas for resistance to Fusarium root rot resulted in inconsistent disease severity across varieties. In 2015, F. avenaceum infested field plots were more heavily damaged based on emergence and yield than F. solani infested plots, and opposite trends were observed in 2016. Differences in root rot severity between years could be due to F. solani infestation causing more damage under warmer temperatures, while plots infested with F. avenaceum caused more damage under cooler temperatures. These results highlight the difficulties observed when screening for soil-borne pathogens, and the increased difficulties when a pathogen complex and changing environmental conditions are involved.

No description available.

Thesis (DSc (Biochemistry))--Stellenbosch University, 2009. / The fumonisin mycotoxins are known to be the causative principle for several animal diseases and are associated with the development of liver and oesophagus cancer and neural tube defects in humans. The thesis focuses mainly on the characterisation of the compounds from maize cultures of the fungus Fusarium verticillioides, isolated from maize, the toxicological effects in animals, mechanism involved in hepato- and nephrocarcinogenicity and discussing the major differences and contradictions in the literature together with their impact on setting relevant risk assessment parameters to safeguard human health. Controversies include the importance of non-genotoxicity vs genotoxicity in the development of cancer, the role of threshold effects in carcinogenesis and the establishment of realistic risk assessment parameters that will also be applicable in developing countries. Recent approaches suggest that thresholds should also apply for genotoxic carcinogens as interaction with the DNA is only one event in the multi-step process of cancer development and therefore could not be taken as the basis for applying a no-effect threshold for genotoxins. It would appear that a carcinogen such as fumonisin, whether it is labeled genotoxic or non-genotoxic per se, exhibits some degree of risk at any level due to additive or synergistic interactions with other xenobiotics and/or dietary constituents. The underlying mechanisms of fumonisin-induced carcinogenicity includes the disruption of sphingolipid, phospholipids and fatty acid metabolism, which plays a major role in the modulation of apoptotic and cell proliferative pathways related to cancer development. Interactive responses between arachidonic acid and ceramide affect downstream cell signal transduction pathways and depending on the cell type the disruption of these pathways could either stimulate or inhibit cell proliferation which eventually will determine the induction of apoptosis and hence affect cell survival. The modulating roles of dietary constituents such as vitamins, protein and the South African herbal teas are also highlighted as they affected the outcome of toxicological assays, thus determining thresholds of the adverse effects in specific target organs that will impact risk assessment parameters. Regulation of the fumonisins in food and the associated risk are debated from many perspectives. In developing countries there is a lack of quality control implying that maize highly contaminated with mycotoxins may directly enter the food chain of adults and children as control of mycotoxins is difficult or in some cases totally absent. The interaction of politics, economy and technology will eventually determine the impact on health as the regulation of fumonisin in food differs between countries. Knowledge about the biological effects of the fumonisins is currently playing an important role in the development of simple and inexpensive methods to reduce the levels of the fumonisin in maize by targeting specific populations at risk.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007. / Submitted to the African Centre for Crop Improvement. Full text also available online. Scroll down for electronic link.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.