The Development of Asexual Systems for Apple Cultivar Improvement

172 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.The apple (Malus xdomestica Borkh.) is an important food crop in most regions of the world. Its growth in tissue culture has become quite common and in vitro apple propagation has become a commercial reality.Hormonal and environmental factors affecting apple shoot proliferation in vitro were investigated. An effective rooting system was developed for in vitro-proliferated apple shoots. Various factors affecting rooting in peat plugs were investigated. Tissue culture-derived stomates seemed to be non-functional. No trichomes were observed on leaves and stems of tissue culture-grown apple shoots. The lack of trichomes might interact with the wide open (non-functional) stomates of tissue culture-derived leaves to cause severe water loss.Adventitious shoot formation is important in the production of new cultivars via sports. Various environmental and internal factors which might affect in vitro adventitious shoot formation were investigated. Medium components, dark pre-treatment, and disinfestation method affected adventitious shoot formation from embryonic axis-free apple cotyledons. Adventitious shoot formation was investigated from early stage of fruit to fruit in cold storage. Adventitious shoot formation also was observed from four apple cultivars and 3 different crabapple species.A very simple and effective in vitro cedar-apple rust inoculation system was developed. Using this system, variation in terms of rust resistance between pre-formed embryonic and adventitious shoots were investigated. This system can be used to select rust resistant apple shoots in vitro.Among 4 different auxins, 2,4-D produced the largest amount of callus. IBA produced less callus while IAA and NAA produced little callus. IBA usually produced very friable callus consisting of elongated cells while 2,4-D and NAA had a tendency to produce hard callus consisting of round cells. Large numbers of protoplasts were isolated from cell suspensions and friable callus cultures of MM.106 apple rootstock. However, only a small percentage of the protoplasts divided. No colony formation was observed.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD