Year: 2007
Type: dissertation
Abstract: The evaluation of environmental and genotypic effects on fruit physical and\nchemical characteristics enables assessment of the feasibility of selecting diploid and/or\ntriploid cultivars for either specific or more diverse locations. Isolation and\ncharacterization of genes encoding enzymes in the carotenoid biosynthetic pathway\nprovides fundamental genetic information which can facilitate breeding of watermelon\ncultivars having desirable flesh colors and enhanced beneficial carotenoids.\nFor the environmental studies, the effects of deficit irrigation on lycopene content,\ntotal soluble solids, firmness, and yield of diploid and triploid watermelon were\nevaluated in different locations and growing seasons. Irrigation regimes were 1.0\nevapotranspiration (ET), 0.75 ET, and 0.5 ET. To investigate if there is a consistent\nresponse in cultivars across diverse locations, studies were conducted in three distinct\nTexas regions. Deficit irrigation reduced total marketable yield, and increased the yield\nof small fruits. Location and irrigation regimes had major influences on yield. Soluble\nsolids content increased with deficit irrigation at 0.5 ET in triploids, but not in diploids. Flesh firmness also increased in triploids compared to diploids. Lycopene content\nincreased with maturity at all irrigation regimes and cultivars. This work confirms that\ndeficit irrigation directly reduces yield, but does not reduce lycopene and fruit quality of\nthe triploids used in this study. From the genetic studies, a total of eight genes encoding\nenzymes in the carotenoid biosynthetic pathway were isolated and characterized. Two\nmembers of the phytoene synthase (PSY) gene family were identified; PSY-A was\nexpressed in all type of tissues, but PSY-B transcript was detected only in ovary, leaf, and\nroot tissues. Gene expression of carotenoid isomerase (CRTISO) was not detected in\nsalmon yellow. A color inheritance study of watermelon flesh indicated that a single\ngene might determine color difference between canary yellow and red without an\ninhibitory effect. A cleaved amplified polymorphic sequence (CAPS) marker developed\nfrom the SNP marker tagging two different lycopene β-cyclase (LCYB) alleles cosegregated\nperfectly with color phenotypes. It was concluded that color determination\nmay be due to a reduced activity of LCYB enzyme in red, whereby a phenylalanine is\nconserved among canary yellow and valine is conserved among red watermelon.
Author: Hae Jeen Bang
Language: English
Subfield: Genetics
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2294515922