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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Plant, Soil & Insect Sciences

Year Degree Awarded

2014

First Advisor

Allen V. Barker

Second Advisor

Geunhwa Jung

Third Advisor

Yeonhwa Park

Subject Categories

Horticulture | Other Plant Sciences | Plant Sciences

Abstract

The mineral nutrient density of vegetables has fallen in the past fifty years. As a result, some people are suffering chronic diseases due to shortage of mineral elements in these foods. The causes of this decline in nutritive value of vegetables have been attributed to a depletion of soil fertility and to a decrease in nutrient concentration in modern cultivars of vegetables. Lettuce (Lactuca sativa L.) is the most widely used leafy vegetable around the world. Research is needed to develop a nutrient content of lettuce that was help to supply adequate mineral nutrition to people. The objectives of the study are to determine if the mineral nutrient densities of lettuce can be increased through cultivar selection and soil fertility practices and to assess genetic diversity of the selected cultivars with use of molecular markers. This experiment was conducted with lettuce grown in organic and conventional fertility management practices in a greenhouse and in field sites. Butterhead, Romaine, and Loose-leaf phenotypes were selected in Heritage and Modern groups of lettuce. Eighteen lettuce cultivars were used from among three phenotypic groups with half of the varieties being Heritage and half being Modern cultivars. Commercial organic and water-soluble nutrient solutions (including Hoagland No. 1 Solution and 20-10-20 Peat Lite) were used in the greenhouse experiments. In the field, compost, organic, and conventional fertility regimes were used. Molecular diversity tested phenotypes and cultivars of lettuce through use of EST-SSRs markers. Growth parameters of height and fresh and dry weights were reported for the experiment. Elemental analysis of P, K, Ca, Mg, S, Mn, Fe, Cu, and Zn were conducted by ICP spectrophotometry. Generally, no differences or only small differences in nutrient accumulation were noted between Heritage and Modern cultivars in the greenhouse or field. Differences among phenotypes were small with somewhat higher accumulations of nutrients occurring with the Loose-leaf and Romaine cultivars than with the Butterhead cultivars. However, large differences in nutrient accumulation occurred among cultivars. ‘Red Deer Tongue’, ‘Forellenschluss’, ‘Winter Density’, ‘Coastal Star’, ‘Simpson Black-Seeded’, and ‘Tom Thumb’ were high in P, K, Ca, Mg, and Zn contents. ‘Two Star, ‘Tropicana’, ‘Red Rosie’, ‘Simpson Elite’, ‘Focea’, and ‘Claremont’ were low in these elements. Overall, in the field, the conventional fertility regime showed higher produce yield than compost or organic fertility regimes. Modern and Loose-leaf types of lettuce showed higher weight yields than Heritage or Butterhead varieties. In the greenhouse, higher elemental accumulation occurred in conventional organic and Hoagland no. 1 fertility regimes than with a conventional fertilizer (20-10-20 Peat Lite), and accumulation was higher in Loose-leaf and Romaine lettuce than in Butterhead cultivars. In molecular assessment, higher heterozygosity was observed in Loose-leaf than in Romaine or Butterhead types. These studies allowed assessments of cultivars and management of conventional fertilizers on the accumulation of nutrients in lettuce and determination of genetic diversity. It is clear that varietal differences occur among cultivars of lettuce and that accumulation of nutrients can be controlled by management of the fertility regimes. Organic and conventional management might be equally effective as long as adequate plant nutrition is provided by each regime.

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