Field trials were conducted to evaluate the effect of quizalofop-ethyl on quackgrass plants in a potato cropping sequence. Fall and summer applications were compared for their quackgrass control potential. Season-long quackgrass control was obtained with quizalofop-ethyl at 96 g/ha following summer application. An increase in the rate of quizalofop-ethyl did not further improve control. Yields with quizalofop-ethyl at 96 g/ha were similar to standard treatments sethoxydim and fluazifop-butyl at recommended rates. Quackgrass control following a summer application was not maintained through to the following season. Fall applications did not result in adequate control of quackgrass the following season at any of the quizalofop-ethyl rates tested.

The enrichment of B-carotene, a precursor to vitamin A, in the local sweetpotato (Ipomoea batatas L.) cultivars is an attractive option in order to improve vitamin A intake in Zambia. The study was conducted to: 1) identify sweetpotato genotypes high in B-carotene content and high root dry mass (RDM) and to determine their combining ability, as measured through their progeny performance; and 2) screen progeny for root characteristics, yield, B-carotene content, and RDM. Firstly, a participatory rural appraisal (PRA) was conducted to determine the consumer preferences for sweetpotato. These preferences would form the basis for selecting desirable genotypes. Secondly, five selected parents were crossed in a full diallel for genetic variance studies. A selected subset of the diallel progeny were evaluated in three environments. Thirdly, 15 polycross progeny were evaluated for stability in five environments using additive main effect and multiplicative interaction (AMMI). The PRA revealed that consumers preferred high RDM combined with high fresh root yield. The diallel crosses recorded significant general combining ability (GCA) and specific combining ability (SCA) effects for B-carotene, RDM, harvest index (HI) and root fresh yield (RFY). The ratios of GCA to SCA variances were large (0.68-0.92). Two high B-carotene parents exhibited positive high GCA effects, indicating that additive gene effects were predominant in the inheritance of B-carotene. Reciprocal mean squares were not significant for RDM but they were significant (p=0.01) for B-carotene content. The estimate of narrow sense heritability of RDM (76.3%) was high; but heritability of B-carotene (20.9%), HI (29.1%) and RFY (34.9%) were much lower. These results suggest that rapid genetic gains should be possible with mass selection breeding techniques based on the phenotype of the parent for RDM but progress will be slow for B-carotene content HI, and RFY. The AMMI analysis identified progeny G2 (B-carotene content = 5.0 mg 100 g-1 and RDM = 37%), G6 (B-carotene content = 4.7 mg 100 g-1 and RDM = 37%), and G8 (B-carotene content = 4.7 mg 100 g-1, RDM = 35%) from the polycross as stable across environments for both B-carotene content and RDM. Genotype G3 was best suited to one of the test environments and had the highest B-carotene content (9.421 mg 100 g-1) and a high RDM (35.47%). / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

The application of pulsed electric fields (PEF) in food processing is a novel technique that requires careful study. In addition, improved understanding of the effect of PEF parameters on both physical and qualitative attributes of agrifood products is a requirement for the application and control of this emerging technology. PEF parameters investigated were pulse widths of 100, 200, and 300 mus, with electric field strengths of 0.75 and 1.5 kV/cm. The amount of pulses used for apples was up to 60, whereas up to 120 pulses were used for potatoes. Initially, apple and potato slices were exposed to various combinations of PEF parameters in order to evaluate the change in their electrical conductivities as an indicator of the disruption of the cell membrane. Subsequently, the impact of PEF on color and texture attributes was studied. In the final set of experiments, PEF was applied as a pre-treatment in order to accelerate the diffusion of moisture in a convective air-drying process at 70°C. / Results regarding the electrical conductivity and the changes in color revealed the similar effect of applying pulses with 100, 200 and 300 mus of duration. Increasing the number of pulses and/or the electric field strength resulted in increased electrical conductivity and discoloration rates of samples. PEF reduced the compressive strength of apple tissues between 21 to 47%. However, the compressive strength of potato tissues did not seem to be affected by the application of PEF. When PEF was applied as a pre-treatment, it caused an increase of up to 30% in the moisture diffusion coefficients of potatoes. In the case of apples, PEF pre-treated samples did not show any increase in drying rates.

The root system is a vital and dynamic part of a plant throughout its lifetime. Its spatial distribution is the consequence of multiple interactions with the surrounding soil medium. In particular, the presence of pathogens in soil may influence the development of the plant, especially the below-ground part, in both its physiology and its structure. Studies of diseased plant roots may take different approaches and investigate disease effects at different levels. In this study, two groups of four potato (Solanum tuberosum L.) plants were grown in middle-sized plastic pots in a greenhouse, and their root systems, together with the soil medium (i.e., sieved and autoclaved homogeneous sand), were submitted to computed tomography (CT) scanning every two weeks until 10 weeks after planting. For the "diseased" group, sand was inoculated with Streptomyces scabies EF-35, the causal agent of potato common scab, at the time of planting. Disease effects on tissue density of roots and below-ground organs, space occupancy and complexity were assessed by analyzing the CT scanning data in the spatio-temporal approach. Fluctuations of tissue density over time were different, on average, between the two groups. They were characterized by an increase of density in Week 2 for the diseased group, reflecting a hardening of tissue, and a delayed decrease relative to the "healthy" group, suggesting a slower transfer of energy from the seed potato to growing roots. Space occupancy, which was studied via volumetric growth rates evaluated from CT scan data, and complexity, which was quantified by the fractal dimension estimated from skeletonized 3-D images constructed from CT scan data, also showed differences in the first part of the experiment. Original analytical procedures based on data transformation and curve fitting in histogram analysis of CT numbers were developed to obtain those results. In conclusion, the new approach presented here, which is based on the advanced processing of CT scanning data collected over time on developing plant root systems and below-ground organs, can be recommended for future phytopathological applications.

Potato is one of the most important crops grown in Canada and all over the world. Late blight caused by P. infestans is one of the major diseases of potato and is mainly managed by fungicides application. The extensive use of fungicides not only causes adverse effects on the environment but also accelerates the development of resistance in this pathogen. Horizontal resistance is considered as the best choice to control P. infestans as it is durable over years. Breeding for durable resistance requires evaluation of hundreds of breeding lines in greenhouses and in the field. This is usually done by testing several epidemiological parameters such as infection efficiency, lesion size, latent period, and area under disease progress curve (AUDPC). These methods are time-consuming and expensive. The present study reports standardization of metabolic profiling protocols and exploration of metabolic profiling based on GC/MS as an additional tool to discriminate resistance in potato against late blight. Potato cultivars varying in horizontal resistance against late blight have been inoculated with water or the pathogen and more than 100 metabolites have been tentatively identified by GC/MS. Univariate analysis has been used to identify several pathogenesis related (PR) and defense related (DR) metabolites that have potential for application as resistance biomarker metabolites. Multivariate analysis of the abundances of metabolites (the mass spectral (MS) ion trap detector outputs were obtained using Saturn Lab Software Version 5.52 and these abundances are positively proportional to the concentration of mass ions of metabolites) in cultivars were mainly used to identify pathogenesis and resistance functions. Following pathogen inoculation, several metabolites such as amino acids, organic acids, fatty acids and sugars, were significantly increased in abundances, especially in the resistant cultivar. Other metabolites such as phenylalanine, tyrosine, shikimic acid and malonic acid detected here are well known for their direct participation in the shikimic acid, the phenylpropanoid, and the malonic acid metabolic pathways. These pathways lead to the production of several defense metabolites including antimicrobial compounds including phenolics, flavonoids and phytoalexins. The metabolic profiling technology developed here has the potential application for screening of potato breeding lines for horizontal resistance against late blight.

The purpose of this thesis is to design a computer model which compares three sprinkler irrigation systems---portable pipe with volume gun, traveller with volume gun and towable/non-towable centre pivot---for potato production. The model user is required to enter a set of basic data: crop and field conditions, irrigation technical parameters and basic economic data, following which the model establishes the preliminary irrigation system and a comparative investment analysis. The model was applied and tested on a potato farm situated in Notre-Dame-de-la-Paix (southwestern Quebec). Based on a 14-year climatic analysis, supplemental irrigation for a normal rainfall growing period (368 mm) was estimated at 250 mm. The application of the model indicates that for a normal rainfall period with an assumed yield increase of 25% over non-irrigated production, all three systems provide net profits (increases of 11% to 50%). However, when determining the Internal Rate of Return (IRR) on a 10-year period, the maximum rate attained by the more profitable systems---portable pipe and non-towable centre pivot (both with an electric pump)---was 14%, a rate inferior to the IRR for non-irrigated production (17%). The Net Present Value (NPV) analysis for the two most profitable irrigation systems provided a slightly higher NPV value for irrigated than for non-irrigated production ($10,942---irrigated vs $10,522---non-irrigated production). The payback period for those two irrigation systems was 7 years. Greater gains of irrigated over non-irrigated yields would be expected for a dry period because of low and unpredictable yields in non-irrigated conditions. A farmer planning to invest in an irrigation system must carefully investigate all technical and socio-economic aspects. The model presented gives the farmer a useful tool with which to do this.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2004. / Härtill 4 uppsatser.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.) in Plant, Soil and Environmental Sciences--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 88-93).

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 405-414). Also available on the Internet.