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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
2011 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
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 is in preparation 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. This study will be continued in 2011. 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 is in preparation. 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.


4.Accomplishments
1. Determination of genotype and environment on levels of watermelon L-citrulline, an amino acid believed to help regulate blood pressure. Preliminary studies suggested that genotype and environment affect L-citrulline content in watermelon, but a comprehensive study was needed, with the ultimate goal to optimize and stabilize fluctuations of this healthful amino acid in watermelon. ARS scientists at Lane, OK, and Charleston, SC, in cooperation with Texas A&M University and North Carolina State University scientists, identified watermelon germplasm with high levels of L-citrulline expression. Additionally, the role environment plays in accumulation of this amino acid was determined. Identification of high expressing germplasm will allow watermelon breeders to select parents for developing high L-citrulline cultivars. Identification of environmental effects on L-citrulline content will aid producers in increasing the content of amino acid in their watermelon.

2. Identification of a novel pigment in a rare watermelon flesh color. Breeding for high carotenoid (phytonutrient present in watermelon) content of watermelon is a time- and cost-consuming effort for watermelon breeding. ARS scientists at Lane, OK, and Charleston, SC, in cooperation with Texas A&M University and the Newe Ya'ar Research Center (Israel) scientists, identified the pigment responsible for a rare watermelon flesh color 'green' which is also a micro-color component in some yellow-fleshed watermelon. This trait is linked to low carotenoid levels, and this finding helped elucidate genetic steps involved in low versus high carotenoid accumulation in watermelon. This information will help breeders determine which parental lines to use when developing high carotenoid cultivars.


Review Publications
King, S., Davis, A.R., Zhang, X., Crosby, K. 2010. Genetics, breeding and selection of rootstocks for Solanaceae and Cucurbitaceae. Scientia Horticultureae. 127:106-111.

Fish, W.W., Bruton, B.D., Russo, V.M. 2009. Watermelon juice: A promising feedstock supplement, diluent, and nitrogen supplement for ethanol biofuel production. Biotechnology for Biofuels. 2:18.

Zhou, X.G., Everts, K.L., Bruton, B.D. 2010. Race 3, a new and highly virulent race of Fusarium oxysporum f. sp. niveum causing Fusarium wilt in watermelon. Plant Disease. 94(1):92-98.

Zhou, X.G., Everts, K.L., Bruton, B.D. 2010. Potential impact of a new highly virulent race of Fusarium oxysporum f. sp. niveum in watermelon in the USA. Acta Horticulturae. 871:535-542.

Last Modified: 4/20/2014
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