Differentiation of Callus and Root Initiation in Pinus banksiana Seedling Cuttings

Jack pine (Pinus banksiana Lamb.) is an important forest species in the Lake States Region and across Canada to the Rocky Mountains. Jack pine can maintain itself on unproductive, dry, nutrient poor soils. Opportunities for genetic improvement within the species are numerous as wide variations are found in vigor, wood and cone characteristics, stem and crown form, and insect and disease resistance. Vegetative propagation is an important tool used in stock improvement. Through vegetative propagation genetically superior stock may be introduced quickly into tree improvement programs. Some tree taxa, for example Salix and Populus, root quite easily because they contain preformed root initials (Carlson, 1938). However, latent root initials have not been described for any of the conifers commonly used in forestry (Dalgas, 1973). In these hard-to-root species, root initiation has been found in callus (Satoo, 1955), a tissue composed of large thin-walled cells developing as a result of injury (Esau, 1977). An accurate understanding of the processes and factors affecting root initiation in cuttings of Pinus species is lacking. Nienstadt et al. (1958) say, "The mysteries of root initiation (in cuttings) remain mostly unsolved . . . We are aware of the important environmental factors governing rooting but we know extremely little of the internal mechanisms controlling root initiation . . ." I have attempted to study the development of callus on seedling cuttings of Pinus banksiana and the development of roots and associated anatomical features in that callus. Material for this study, supplied by Dr. Bruce Haissig, plant physiologist, at the U.S. Forest Service Forestry Sciences Laboratory in Rhinelander, Wisconsin, was control (untreated) material from a physiology study of effects of different growth substances on root initiation