From buds to shoots: Insights into grapevine development from the Witch's Broom bud sport

Premise of Study Development is relatively understudied in woody vines, such as grapevine (Vitis vinifera). We used the Witch's Broom bud sport in grapevine to understand the developmental trajectories of the bud sports, as well as the potential genetic basis of the bud sport. Methods We phenotyped shoots, buds, and leaves of two independent cases of the Witch's Broom bud sport, in the Dakapo and Merlot varieties of grapevine, alongside wild-type counterparts of the same variety. We also performed Illumina and Oxford Nanopore sequencing on the two independent cases and two wild-type counterparts of the same variety. Key Results The Dakapo and Merlot cases of Witch's Broom displayed severe developmental defects, with no fruit/clusters formed and dwarf vegetative features. However, the Dakapo and Merlot cases of Witch's Broom studied were also phenotypically different from one another, with distinct differences in bud and leaf development. We were able to identify unique genetic mutations in our two Witch's Broom cases that are strong candidates for the genetic basis of the bud sports. Conclusions The Witch's Broom bud sport in grapevine serves as a useful natural mutant in which to study grapevine development. The Witch's Broom bud sports in both varieties studied had dwarf phenotypes, but the two instances studied were also vastly different from one another. Future work on Witch's Broom bud sports in grapevine could provide more insight into development and the genetic pathways involved in grapevine. ### Competing Interest Statement The authors have declared no competing interest.