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United States Department of Agriculture

Agricultural Research Service

Research Project: PHYSIOLOGICAL AND GENETIC BASIS OF POSTHARVEST QUALITY, DISEASE CONTROL, AND PHYTONUTRIENT CONTENT OF WATERMELONS
2012 Annual Report


1a.Objectives (from AD-416):
Objective 1: Determine impact(s) of pre-harvest production and post-harvest handling and storage factors on quality, including phytonutrients, for watermelon. Sub 1A. Evaluate effects of gene sequences, linkages, and other genetic factors on human health bioactive compounds in watermelon germplasm. Sub 1B. Determine effects of pre-harvest diseases, environmental conditions, and cultivars on carotenoid and free amino acid levels in watermelon. Sub 1C. Elucidate the effects of post-harvest storage/handling time and temperature on carotenoid and free amino acid levels in watermelon. Objective 2: Develop analytical methods/screening techniques/molecular markers for L-citrulline, L-ornithine, carotenoids, and other human health bioactive compounds in watermelon. Sub 2A. Determine inheritance/sequence of carotenoid genes in watermelon. Sub 2B. Develop analytical methods to quantify free amino acids, including L-citrulline, L-ornithine and other bioactive compounds. Sub 2C. Develop processes for economical extraction and purification of value-added components of watermelon.


1b.Approach (from AD-416):
Experiments to evaluate the effects of gene sequences, linkages, and other genetic factors on human health bioactive compounds in watermelon will be conducted. Analytical methods to quantify free amino acids, including L-citrulline, L-ornithine, and other bioactive compounds will be developed, along with processes for economical extraction and purification of value-added components of watermelon fruit. The effects of post-harvest storage/handling time and temperature on carotenoid and free amino acid levels in watermelon will be elucidated. The effects of pre-harvest diseases, environmental conditions, and cultivars on carotenoid and free amino acid levels in watermelon will be determined.


3.Progress Report:
This project began 4/21/11 and terminated 1/12/12, due to FY12 Appropriation that directed the Unit closure. Progress was made on the two objectives and their six sub-objectives over the first year of research directed at developing value-added products from watermelon fruit. Under Research Objective 1A, watermelon from 50 varieties were grown at two locations. Approximately 1,500 watermelon flesh samples were taken for bioactive compound quantification (carotenoids, L-citrulline, and glutathione) and for DNA extraction. A paper was submitted on L-citrulline accumulation as affected by environment and genotype, another paper was prepared on bioactive compound accumulation as affected by ploidy level. Under Research Objective 1B, pre-harvest production factors on phytonutrient levels in watermelon, 20 varieties of watermelon were grown on location. Daily soil and weather conditions and disease scores were recorded. Ripe fruit were harvested, and flesh and rind samples were collected and stored frozen for subsequent analyses for carotenoids and amino acids. The greater than average rainfall in 2010 precluded a drought-stress study on watermelon citrulline levels. Under Research Objective 2A, five watermelon populations segregating for carotenoid expression were produced. Carotenoid content was determined, and DNA samples were collected for future testing. A manuscript on a novel color mutant was prepared. Under Research Objective 2B, the development of analytical methods for human health bioactive compounds in watermelon, methodology for quantitative extraction of physiological amino acids from cucurbit fruit was developed. Similarly, an existing HPLC methodology was optimized to separate dabsylated physiological amino acids extracted from cucurbit fruit. Physiological amino acids from the rinds and flesh of the 20 watermelon cultivars grown in 2010 were quantified by this newly developed methodology. Under Research Objective 2C, the development of a scalable process for the production of L-citrulline from watermelon flesh and rind, bench-scale experiments were performed to develop methods to release and isolate citrulline. It was found that mechanical pressing of flesh or rind released about 90% of the citrulline and other amino acids in the juice. A freeze/thaw step before the mechanical squeeze increased citrulline recovery to greater than 90%. Separation of the citrulline from the watermelon juice was subsequently carried out by adsorption of the amino acids in the juice onto a cation exchange resin such as Dowex 50 at pH 3. The amino acids were eluted from the column with 1M base (e.g., NaOH). Citrulline is obtained at a purity of 80-85% and a yield of greater than 80% at this step. If desired, further purification of the citrulline can be effected by crystallization. No research was conducted during FY12; all efforts were directed toward the efficient finalization of this project.


Review Publications
Fish, W.W. 2012. Refinements of the attending equations for several spectral methods that provide improved quantification of B-carotene and/or lycopene in selected foods. Postharvest Biology and Technology. 66:16-22.

Zhang, H., Guo, S., Gong, G., Ren, Y., Davis, A.R., Yong, X. 2011. Sources of resistance to race 2WF powdery mildew in U.S. watermelon plant introductions. HortScience. 46(10):1349-1352.

Davis, A.R., Webber III, C.L., Fish, W.W., Wehner, T., King, S., Perkins-Veazie, P. 2012. L-citrulline levels in watermelon cultigens tested in two environments. HortScience. 46(12):1572-1575.

Bruton, B.D., Fish, W.W. 2012. Myrothecium roridum leaf spot and stem canker on watermelon in the southern Great Plains: Possible factors for its outbreak. Plant Health Progress. Available: doi:10.1094/PHP-2012-0130-01-BR.

Sikora, E.J., Bruton, B.D., Wayandande, A.C., Fletcher, J. 2012. First report of the cucurbit yellow vine disease caused by Serratia marcescens in watermelon and yellow squash in Alabama. Plant Disease. 96(5):761.

Fish, W.W., Bruton, B.D., Popham, T.W. 2012. Cucurbit host range of Myrothecium roridum isolates from watermelon. American Journal of Plant Sciences. 3:353-359.

Last Modified: 9/29/2014
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