The evaluation of environmental and genotypic effects on fruit physical and
chemical characteristics enables assessment of the feasibility of selecting diploid and/or
triploid cultivars for either specific or more diverse locations. Isolation and
characterization of genes encoding enzymes in the carotenoid biosynthetic pathway
provides fundamental genetic information which can facilitate breeding of watermelon
cultivars having desirable flesh colors and enhanced beneficial carotenoids.
For the environmental studies, the effects of deficit irrigation on lycopene content,
total soluble solids, firmness, and yield of diploid and triploid watermelon were
evaluated in different locations and growing seasons. Irrigation regimes were 1.0
evapotranspiration (ET), 0.75 ET, and 0.5 ET. To investigate if there is a consistent
response in cultivars across diverse locations, studies were conducted in three distinct
Texas regions. Deficit irrigation reduced total marketable yield, and increased the yield
of small fruits. Location and irrigation regimes had major influences on yield. Soluble
solids 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
increased with maturity at all irrigation regimes and cultivars. This work confirms that
deficit irrigation directly reduces yield, but does not reduce lycopene and fruit quality of
the triploids used in this study. From the genetic studies, a total of eight genes encoding
enzymes in the carotenoid biosynthetic pathway were isolated and characterized. Two
members of the phytoene synthase (PSY) gene family were identified; PSY-A was
expressed in all type of tissues, but PSY-B transcript was detected only in ovary, leaf, and
root tissues. Gene expression of carotenoid isomerase (CRTISO) was not detected in
salmon yellow. A color inheritance study of watermelon flesh indicated that a single
gene might determine color difference between canary yellow and red without an
inhibitory effect. A cleaved amplified polymorphic sequence (CAPS) marker developed
from the SNP marker tagging two different lycopene ò-cyclase (LCYB) alleles cosegregated
perfectly with color phenotypes. It was concluded that color determination
may be due to a reduced activity of LCYB enzyme in red, whereby a phenylalanine is
conserved among canary yellow and valine is conserved among red watermelon.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4949 |
| Date | 25 April 2007 |
| Creators | Bang, Hae Jeen |
| Contributors | Leskovar, Daniel I., Pike, Leonard M. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 916574 bytes, electronic, application/pdf, born digital |
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