Utilizing Anti-auxin to Increase Axillary Shoot Proliferation Rate of Japanese Elm

There are a number of propagation techniques used for elm cultivar production including softwood cuttings, micropropagation and bud grafting. In the nursery trade it is highly desirable to propagate elm cultivars on their own roots. Micropropagation is an ideal propagation method to quickly increase a new cultivar. Japanese Elm [Ulmus davidiana var. japonica (Sarg. ex Rehd.) Nakai] is an outstanding shade tree and because of its inherent Dutch elm disease resistance, several selections and hybrids have been made. In 2014, North Dakota State University released Northern Empress® Japanese elm (U. davidiana var. japonica ‘Burgundy Glow’) in 2014. Northern Empress® is a very hardy, small to medium sized (28’) growing elm with a rounded crown and attractive summer and fall foliage. Fall foliage changes from green to apricot-orange to burgundy-red before leaf drop. Frontier Elm [U. (carpinifolia x parvifolia) 'Frontier'] has similar fall color to Northern Empress®but is not reliably hardy in zone 4. American elm has been shown to perform well in tissue culture except that high levels of shoot basal callus is produced reducing resources for shoot proliferation with Northern Empress® having similar results in preliminary studies. The objective of this study was to establish a micropropagation protocol for Northern Empress® Japanese elm utilizing anti-auxin compound 2-(p-chlorophenoxy)-2-methylpropionic acid (PCIB) to reduce basal callus and increase axillary shoot proliferation. A 3 x 3 factorial of three nutrient salt formulations (DKW, LP, and WPM) and three concentrations of PCIB (0, 5, 10 μM) were used determine shoot growth and shoot proliferation of viable axillary shoots. Nodal explants were 5mm in length and initiated into cultures on the various factorial media plus 2.2 μM 6-benzylaminopurine (BA), 3% sucrose, pH of 6.0 with 0.7% agar. Nodal explants were transferred every 6 weeks for a total culture period of 12 weeks. At each transfer date, data was taken on shoot number and propagation number, which entailed two nodes that were 5±1 mm length of shoot. Based on number of shoots produced per nodal segment and propagation number there was a significant interaction between nutrient salt formulation and PCIB concentration with DKW and 10 μM PCIB significantly producing the most axillary shoots, propagules per nodal segment with reduced basal callus production as compared to other combinations evaluated.