ASHS 2024 Conference

Buttonbush (Cephalanthus occidentalis) is a valuable landscape shrub revered for its prominent white, globe-shaped blooms which can later develop into brilliant red aggregate fruits. This North American native shrub occurs almost exclusively in riparian habitats, typically in standing water in the wild, but it is curiously adaptable to a range of landscape conditions in cultivation. Because this species appears to perform well when grown using average soil-moisture conditions, we questioned where the limits of drought tolerance occur for this riparian-adapted species. The objective of this study was to evaluate USDA-GRIN germplasm of buttonbush to compare unique provenances representing different regions of the native range of the taxon to generate a relative scale of predicted drought tolerance for the species. Utilizing vapor pressure osmometry, this study examined seasonal osmotic adjustment and predicted leaf water potential at the turgor loss point (ᴪpo) among ten Cephalanthus occidentalis populations grown at the Morton Arboretum in Lisle, Illinois. All populations evaluated demonstrated a minor ability to osmotically adjust (Δᴪ𝝿100) throughout the growing season. NA 79917 exhibited the most osmotic adjustment (-0.22 MPa) whereas NA 61271 exhibited the least (-0.08 MPa). Estimated spring ᴪpo and summer ᴪpo across populations was -1.75 MPa and -1.91 MPa, respectively. NA 79705 exhibited the highest ᴪpo in both spring (-1.56 MPa) and summer (-1.68 MPa). NA 82190 exhibited the lowest ᴪpo in spring (-1.92 MPa ), whereas NA 73814 exhibited the lowest in summer (-2.17 MPa). These data indicate that drought tolerance in buttonbush varies across populations, suggesting that this trait can be improved in landscape selections through selective breeding efforts.