College of Agriculture & Natural Resources
Permanent URI for this communityhttp://hdl.handle.net/1903/1598
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Microbial Ecology and Horticultural Sustainability of Organically and Conventionally Managed Apples(2008) Ottesen, Andrea; Walsh, Christopher S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Objectives: Organically and conventionally managed apple trees (Malus domestica Borkh) were evaluated for three growing seasons (2005-2007) to examine the impact of organic and conventional pesticide applications on the microbial ecology of phyllosphere and soil microflora. An important objective was to establish if organic or conventional selection pressures contribute to an increased presence of enteric pathogens in phyllosphere microflora. The horticultural and economic sustainability of the organic crop was also compared to the conventional crop with regard to fruit yield and input costs. Methods: Microbial populations from phyllosphere and soil environments of apple trees were evaluated using clone libraries of 16S rRNA gene fragments. Clones were sequenced and software was used to assess diversity indices, identify shared similarities and compute statistical differences between communities. These measurements were subsequently used to examine treatment effects on the microbial libraries. Phyllosphere Results: Eight bacterial phyla and 14 classes were found in this environment. A statistically significant difference between organically and conventionally managed phyllosphere bacterial microbial communities was observed at four of six sampling time points. Unique phylotypes were found associated with each management treatment but no increased human health risk could be associated with either treatment with regard to enteric pathogens. Soil Results: Seventeen bacterial phyla spanning twenty-two classes, and two archaeal phyla spanning eight classes, were seen in the 16S rRNA gene libraries of organic and conventional soil samples. The organic and conventional soil libraries were statistically different from each other although the sampling depth was not sufficient to make definitive inference about this environment. Horticultural Results: Fruit yields from organically managed apple trees were from one half to one third of the yields from conventionally managed trees. Based on input costs, organic fruit was about twice as expensive to produce. Asian pears (Prunus serotina) were also included in this horticultural analysis and showed greater field tolerance as an organic specialty niche crop than apples.Item GENERIC DIFFERENCES IN ANTIOXIDANT CONCENTRATION IN THE FRUIT TISSUES OF FOUR MAJOR CULTIVARS OF APPLES(2004-05-21) Kandhari, Pankaj; Quebedeaux, Bruno; Food ScienceApples have been cultivated for over two millennia and over 10,000 named cultivars exist. Antioxidants protect against oxidative stress and provide resistance against superficial scald in apple (Malus domestica Borkh). In the present study four commercially important apple cultivars (Red Delicious, Gala, Fuji and Granny Smith) and source leaves of Gala apple tree were studied. Ascorbate concentration, SOD activity, and protein concentration was determined for Gala leaves and all the four apple (fruit peel and fleshy cortex tissue) cultivars. Gala leaves had the highest ascorbate concentration and SOD activity. Granny Smith fruit peel tissue had the highest and Red Delicious fruit peel tissue had the lowest ascorbate concentration. Granny Smith fruit peel tissue had the highest SOD activity. These results demonstrate that ascorbate concentration and SOD activity in apple tissue may depend on their respective breeding parents, scald susceptibility and the amount of ethylene they produce.