Genetic Inheritance and Primary Mapping of Candidate Region Regulating Black Border Seed Trait in Watermelon (Citrullus lanatus)

ABSTRACT Watermelon ( Citrullus lanatus ) is an important crop in the Cucurbitaceae family. In this study, two parental lines with distinct seed border phenotypes were crossed to generate F 1 and F 2 generations. Genetic inheritance analysis of 2 years of phenotypic data showed that a single recessive gene is regulating the black border seed trait. BSA‐seq analysis identified the candidate gene locus related to black border seed ( Clbbs ) in a 3.63 Mb interval on chromosome 3. In 2023, a total of 22 recessive recombinant F 2 plants allowed us to narrow down this region into a 466.07 Kb interval. In 2024, the targeted Clbbs locus was delimited to a 236.33 Kb interval by using another 336‐F 2 plants, and 41 recombinant plants were screened. The final mapping region contained 19 genes and eight genes encoding polyphenol oxidase protein were predicted as the candidate genes due to their involvement in the pigmentation pathway.