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William C. Kelly

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Nihal C. Rajapakse, William B. Miller and John W. Kelly

Low-temperature storage potential of rooted cuttings of garden chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] cultivars and its relationship with carbohydrate reserves were evaluated. Storage of chrysanthemum cuttings at -1 and -3 °C resulted in freezing damage. Visual quality of rooted cuttings stored at 0 or 3 °C varied among cultivars. Quality of `Emily' and `Naomi' cuttings was reduced within a week by dark storage at 0 or 3 °C due to leaf necrosis, while `Anna' and `Debonair' cuttings could be held for 4 to 6 weeks without significant quality loss. In `Anna' and `Debonair', low-temperature storage reduced the number of days from planting to anthesis regardless of storage duration. However, flowers of plants grown from stored cuttings were smaller than those of nonstored cuttings. At the beginning of storage, `Emily' and `Naomi' had lower sucrose, glucose, and fructose (soluble sugars) content compared to `Anna' and `Debonair'. Regardless of temperature, leaf soluble sugar was significantly reduced by dark storage for 4 weeks. In stems, sucrose and glucose were reduced while fructose generally increased during low-temperature storage probably due to the breakdown of fructans. Depletion of soluble sugars and a fructan-containing substance during low-temperature dark storage was greater in `Emily' and `Naomi' than in `Anna' and `Debonair'. Low irradiance [about 10 μmol·m-2·s-1 photosynthetically active radiation (PAR) from cool-white fluorescent lamps] in storage greatly improved overall quality and delayed the development of leaf necrosis in `Naomi'. Cuttings stored under light were darker green and had a higher chlorophyll content. Leaf and stem dry weights increased in plants stored under medium and high (25 to 35 μmol·m-2·s-1 PAR) irradiance while no change in dry weight was observed under dark or low light. Results suggest that the low-temperature storage potential of chrysanthemum cultivars varies considerably, and provision of light is beneficial in delaying the development of leaf necrosis and maintaining quality of cultivars with short storage life at low temperatures.

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Joseph C. Kuhl, Kelly Zarka, Joseph Coombs, William W. Kirk and David S. Douches

Late blight of potato (Solanum tuberosum L.), incited by Phytophthora infestans (Mont.) de Bary, is a devastating disease affecting tuber yield and storage. Recent work has isolated a resistance gene, RB, from the wild species Solanum bulbocastanum Dun. Earlier work in Toluca, Mexico, observed significant levels of field resistance under intense disease pressure in a somatic hybrid containing RB. In this study, five transgenic RB lines were recovered from the late blight susceptible line MSE149-5Y, from the Michigan State University (MSU) potato breeding program. Transgenic lines were molecularly characterized for the RB transgene, RB transcript, and insertion number of the kanamycin resistance gene NPTII. Transgenic lines and the parent line were evaluated for resistance in field and laboratory tests. Molecular characterization alone did not predict which lines were resistant. Three of the RB transformed MSE149-5Y lines showed increased resistance under field conditions at MSU and increased resistance in detached leaf evaluations using multiple isolates individually (US-1, US-1.7, US-8, US-10, and US-14). Transfer of RB into late blight susceptible and resistant lines could provide increased protection to potato late blight. The use of the RB gene for transformation in this way creates a partially cisgenic event in potato because the gene's native promoter and terminator are used. This type of transformation provides a chance to generate greater public acceptance of engineered approaches to trait introgression in food crops.