QUERIES IN QUERCUS: FROM THE DEVELOPMENT OF A TISSUE CULTURE CLONAL PROPAGATION SYSTEM TO THE EVALUATION OF STRESS TOLERANT HYBRID WHITE OAKS FOR THE URBAN ENVIRONMENT

A research program was developed by Miles Schwartz Sax with a focus on researching two key priority areas for the Urban Horticulture Institute (UHI). The first priority area was the creation of a tissue culture system for the clonal propagation of hybrid white oaks. The second priority area was the development of evaluation methods to assess hybrid white oaks and other tree species for tolerance to stresses commonly found in the urban environment. A tissue culture system was developed for the clonal propagation of hybrid white oaks between 2014 to 2018. There were 1,966 buds from 34 genotypes of UHI hybridized white oaks that were attempted in establishment and trialed in a tissue culture system. Individual genotype was the single largest factor affecting successful establishment, multiplication, stabilization and rooting of oaks in a tissue culture system. Fourteen lines of hybrid oaks were identified as having the capacity to stabilize and grow continuously in the tissue culture environment. Multiplication efficiency rates were dependent on individual genotype. This research showed the ability to re-establish genotypes of interest that had been previously established and stabilized in tissue culture. Re-establishment allowed for the possibility of the development of a direct establishment to rooting method that bypasses the time-consuming multiplication phase. A series of studies were undertaken with a focus on refining and simplifying the tissue culture process. These included the use of phenolic binding agent PVP to reduce damage to explants by oxidization, the modification of the subculturing cycles, and the use of isolated terminal buds for explant multiplication. In addition to trialing hybrids oaks, a series of oak species (Q. bicolor, Q. gambelii, Q. macrocrpa, Q. garryana) were trialed in a tissue culture system. This study examined how initial shoot and bud position on the stock plant affected establishment and multiplication rates of oaks in tissue culture. This study found that initial shoot position had no effect on tissue culture efficacy for trees up to four years old. As with hybrid oaks’ successful establishment, multiplication and rooting rates were highly dependent on genotype. This study represents the first time that Q. macrocarpa and Q. garryana were successfully used in a tissue culture system. Lastly, an experiment was undertaken that observed the gas exchange response and changes in turgor loss points of two tree species (Quercus bicolor and Betula pendula) grown under well-watered and drought conditions in limited soil volume. In response to soil water deficit conditions, Q. bicolor reduced its turgor loss point (osmotic adjustment) and maintained gas exchange rates. In contrast, B. pendula shed its leaves, did not reduce turgor loss point, and had varied gas exchange responses. Both species displayed contrasting physiological strategies to cope with drought by showing either an avoidance or tolerance mechanism