Citrullus lanatus (Thunb.) Matsum. & Nakai - Cucurbit Breeding ...

GENERAL CONCLUSIONS
Summary of Findings Presented in the Dissertation
The studies presented herein are a contribution to the understanding of the genetics of rind pattern,
flesh color, and resistance to gummy stem blight in watermelon.
We identified three new genes in watermelon. Scarlet red flesh (Scr) produced a higher intensity red
color in the flesh of 'Dixielee' and 'Red-N-Sweet' compared to 'Angeleno Black Seeded', the type line for red
flesh color in watermelon. Scr was inherited as a single dominant gene. Yellow belly (Yb) was classified as a
single dominant gene changing the color of the ground spot in 'Black Diamond' from creamy white to dark
yellow. The presence of intermittent vs. continuous stripes on the rind of 'Navajo Sweet' was explained by the
action of a single recessive gene that we named intermittent stripes (ins), with the dominant allele present in
'Crimson Sweet'. We confirmed the inheritance of the C gene for the canary yellow flesh as a single dominant
gene. The inbred line NC-517, the canary yellow parent in our study, should be considered the homozygous
public type line for the C gene, rather than the canary yellow F 1 hybrids available so far. We highlighted a new
possibility for the development of watermelon fruit with novel rind: the spotted phenotype (Sp gene) was
successfully transferred from 'Moon and Stars' to cultivars with gray background. The spotted trait was
undetectable on many fruit with light green rind. In addition, the presence of the small spots (stars) was shown
to have a random distribution on fruit and leaves, while the presence of large yellow blotches (moons) was
inconsistent and may be determined by the coalescence of many stars.
Our study highlighted a complex genetic background for the inheritance of red and salmon yellow
flesh colors, previously attributed solely to the expression of the Wf and y genes. Based on our observations, we
discarded the hypothesis of quantitative inheritance and suggested that different genes, or a tissue-specific
expression of the same genes, might be involved in the pigmentation of different portions of the fruit. Our
hypothesis should be further investigated. The tissue-specific identification of the pigments in the fruit of
segregating populations by high performance liquid chromatography (HPLC) would indicate localized
expression of genes and, possibly, indicate a model for pigment development in watermelon, by similarity with
known pathways in other species. The same crosses used in our study could be investigated at first, while new
crosses could be developed for future research.
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