The genetic mechanisms controlling fruit morphology in watermelon is not fully understood. Only one candidate gene, ClSUN25-26-27a (Cla011257), has been identified as a significant contributor to the ovary and fruit shape. ClSUN25-26-27a is a member of the SUN gene family, which has been extensively studied in relation to fruit morphology in tomatoes. In tomato, the effect on fruit shape facilitated by this gene is detectable during the early stages of fruit development, with the cell patterns established pre-anthesis. In watermelon, three alleles of ClSUN25-26-27a are known to be associated with ovary and fruit shape variation: the wild-type, a SNP, and a 159bp deletion in the 3rd exon. This study aims to determine the effect of the novel allelic variation for ClSUN25-26-27a on ovary and fruit shape. Four novel alleles have been identified and sequenced in the coding region of ClSUN25-26-27a across three Citrullus species. Marker assisted backcrossing was used to introgress the different alleles into a common genetic background. The NILs were phenotyped in the field to determine the effect of the novel alleles on ovary and fruit shape. Ovary length and width were measured four days pre-enthesis, at anthesis, and four days post-anthesis and used to calculate the ovary shape index (OSI). Mature fruit was also phenotyped using Tomato Analyzer. One of the novel alleles was significantly associated with ovary and fruit shape. These findings contribute to the understanding of the important SUN gene family and the genetic mechanisms contributing to watermelon fruit shape. Future research will determine the gene expression patterns of the different alleles and the effect of the alleles on the cell number or cell size in watermelon.
