AUTHOR=Paudel Lucky , Clevenger Josh , McGregor Cecilia 

TITLE=Chromosomal Locations and Interactions of Four Loci Associated With Seed Coat Color in Watermelon

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00788

DOI=10.3389/fpls.2019.00788

ISSN=1664-462X

ABSTRACT=<p>Different species of edible seed watermelons (<italic>Citrullus</italic> spp.) are cultivated in Asia and Africa for their colorful nutritious seeds. Consumer preference varies for watermelon seed coat color. Therefore, it is an important consideration for watermelon breeders. In 1940s, a genetic model of four genes, <italic>R</italic>, <italic>T</italic>, <italic>W</italic> and <italic>D</italic>, was proposed to elucidate the inheritance of seed coat color in watermelon. In this study, we developed three segregating F<sub>2</sub> populations: Sugar Baby (dotted black seed, <italic>RRTTWW</italic>) × plant introduction (PI) 482379 (green seed, <italic>rrTTWW</italic>), Charleston Gray (dotted black seed, <italic>RRTTWW</italic>) × PI 189225 (red seed, <italic>rrttWW</italic>), and Charleston Gray (dotted black seed, <italic>RRTTWWdd</italic>) × UGA147 (clump seed, <italic>RRTTwwDD</italic>) to re-examine the four-gene model and to map the four genes. In the dotted black × green population, the dotted black seed coat color (<italic>R_</italic>) is dominant to green seed coat color (<italic>rr</italic>). In the dotted black × red population, the dominant dotted black seed coat color and the recessive red seed coat color segregate for the <italic>R</italic> and <italic>T</italic> genes, where the <italic>R</italic> gene is dominantly epistatic to the <italic>T</italic> gene. However, the inheritance of the <italic>T</italic> locus did not fit the four-gene model, thus we named it <italic>T<sup>1</sup></italic>. In the dotted black × clump population, the clump seed coat color and the dotted black seed coat color segregate for <italic>W</italic> and <italic>D</italic>, where <italic>D</italic> is recessively epistatic to <italic>W</italic>. The <italic>R</italic>, <italic>T<sup>1</sup></italic>, <italic>W</italic>, and <italic>D</italic> loci were mapped on chromosomes 3, 5, 6, and 8, respectively, using QTL-seq and genotyping-by-sequencing (GBS). Kompetitive Allele Specific PCR (KASP™) assays and SNP markers linked to the four loci were developed to facilitate maker-assisted selection (MAS) for watermelon seed coat color.</p>