Prairie willow (Salix humilis) is a compact shrub willow native throughout the eastern United States. Aside from its desirable habit, attractive flowers and foliage, and pervasive ecological associations, prairie willow demonstrates profound adaptability in its native range, offering potential for urban green infrastructure applications. The dwarf variety (S. humilis var. tristis) is particularly favorable for horticultural applications due to its pronounced short stature. However, prairie willow exhibits a unique recalcitrance to traditional asexual propagation techniques commonly employed with willows. Tissue culture, a highly effective means for propagating recalcitrant woody plants, has not been explored for prairie willow. Given its potential horticultural value, tissue culture serves as a promising alternative for commercializing this taxon. This study explored the impact of four concentrations (0mg/L, 0.1mg/L, 1mg/L, and 10mg/L) of the common shoot-inducing hormone BAP (6-benzylaminopurine, a cytokinin) on initial growth in culture. Plant material was harvested from actively growing softwood tissue on a greenhouse-grown stock plant of the dwarf variety (USDA-GRIN accession AMES35806) and was trimmed to 1-2cm single-node explants (N=80, n=20). Sterilization involved an initial rinse in tap water with Tween-20, followed by a 30-second soak in 70% ethanol, a 5-minute soak in 0.9% sodium hypochlorite, and intermittent 5-minute rinses in sterile distilled water. Explants were stuck in 15mL falcon tubes with 4mL of media (2.41g/L woody plant media 30g/L sucrose 7g/L agar BAP). Culture tubes were placed on a light rack (18.3°C) with continuous light (40 watt fluorescent) and monitored weekly. The number of expanded buds and contamination rates were recorded. Contamination rates were low (12.5%), indicating successful sterilization. Development was slow across all treatment groups, suggesting the need for stock plant rejuvenation before propagule harvest. However, days to bud break indicated that 0.1mg/L BAP may result in the quickest shoot proliferation. Percentages of explants with expanded buds by week 5 were 13% (0mg/L), 68% (0.1mg/L), 41% (1mg/L) and 6% (10mg/L). All explants in 10mg/L exhibited browning and necrosis by week 5, while all but 5% of explants in 0mg/L remained green despite limited bud expansion. Future trials will investigate rejuvenation and alternative cytokinins to generate a complete protocol for introducing prairie willow into tissue culture. This research supports the integration of this versatile plant into commercial production, enhancing the ornamental plant palette for challenging urban landscapes.
