Genetic analysis and mapping of a short-internode gene (cladw) in watermelon (Citrullus lanatus L.)

Internode length (IL) is an important characteristic of plant architecture of watermelon (Citrullus lanatus L.). A dwarf type plant phenotype can support the greater planting density and land utilization for well growth of crop plants. In this study, two watermelon lines "W1-1 (standard vine) and ZXG01061 (dwarf vine)” were used as parental lines and F1, F2, BC1P1 and BC1P2 generations were developed for dwarf trait inheritance analysis and candidate gene identification. Genetic analysis of two year's collected phenotypic data indicated that watermelon dwarfism was regulated by a single recessive gene (cladw). Bulked segregant analysis sequencing (BSA-seq) total of 1.24-Mb genomic region harbouring the candidate dwarfism gene on chromosome 9. Fine genetic with 1,097 F2 plants signified that the cladw locus was finally delimited to a 203-kb region containing 10 candidate genes (including five genes annotated as GID1L2 gibberellin (GA) receptors). Endogenous hormone quantification analysis also showed that the internode GA content of ZXG01061 was higher than that of W1-1. When ZXG01061 plants were treated with exogenous application of GA3, then original plant height was not recovered, indicating that ZXG01061 is GA insensitive. Further, Cla010254 and Cla010256 (annotated as gibberellin receptor GID1L2) exhibted base deletions in ZXG01061 compared with W1-1. The expression of Cla010254 in W1-1 was significantly higher than that of ZXG01061. In conclusion, our results indicated that Cla010254 is a candidate gene for regulating the watermelon dwarfism trait.