Fine Mapping of Bush Gene and Development of Molecular Marker for Bush Type in Pumpkin (Cucurbita maxima Duch.)

The bush trait is an important agronomic trait with great value for pumpkin crops. In this study, a bush-type line, CS82, identified in pumpkin (Cucurbita maxima) showed no obvious main vine, and all petioles clustered at the extremely shortened stem with limited internodes. The microscopy analysis revealed that the bush-type phenotype may be due to the degeneration of the shoot apex. Genetic analysis showed that the bush-type phenotype is controlled by a single dominant nuclear gene. Exogenous gibberellin treatment could not recover the bush-type phenotype to the wild type, indicating that the bush-type phenotype is not due to the mutation of gibberellin biosynthesis genes. The BSA-seq analysis preliminarily mapped the Bush gene to Chr.15 of the pumpkin genome. Further fine mapping limited the Bush gene to a physical distance of 95.65 kb with 19 genes. Based on the gene function and the 63 bp deletion, CmaCh15G011490, encoding an axial regulator YABBY 5-like protein, was selected as the candidate gene for the Bush gene. A quick and efficient method was developed for bush-type phenotype identification, which is useful for bush-type variety breeding in pumpkin.