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

Internode length is an important plant type characteristic of watermelon (Citrullus lanatus L.). A dwarf phenotype can increase plant density and land utilization. In this study, W1-1 (standard vine) and ZXG01061 (dwarf) were used as the parental lines to create F1, F2, BC1P1 and BC1P2 progenies for dwarf trait inheritance analysis and candidate gene identification. Genetic analysis indicated that the watermelon dwarf trait was regulated by a single recessive gene (cladw) with phenotypic data collected over two years. The bulked segregant analysis (BSA-seq) revealed a 1.24 Mb genomic region harbouring the candidate dwarfing gene on chromosome 9. Through initial and fine mapping with 1,097 F2 plants, the cladw locus was finally delimited into a 203 kb region containing 10 candidate genes (including five genes annotated as GID1L2 gibberellin GA receptors). Hormone analysis showed that the GA content of the ZXG01061 internode was higher than that of W1-1. When ZXG01061 plants were treated with exogenous GA, the original plant height could not be recovered, indicating that ZXG01061 is GA insensitive. Cla010254 and Cla010256 (annotated as gibberellin receptor GID1L2) in ZXG01061 had base deletions compared with W1-1. The expression pattern of Cla010254 in W1-1 was significantly higher than that in ZXG01061. In conclusion, our results indicate that Cla010254 is a candidate gene for watermelon dwarfing.