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Japanese barberry (Berberis thunbergii DC.) is a widespread invasive plant that remains an important landscape shrub represented by ornamental, purple-leaved forms of the botanical variety atropurpurea. These forms differ greatly in appearance from fetal plants, bringing into question whether they contribute to invasive populations or whether the invasions represent self-sustaining populations derived from the initial introduction of the species in the late 19th century. In this study we used amplified fragment length polymorphism (AFLP) markers to determine whether genetic contributions from B. t. var. atropurpurea are found within naturalized Japanese barberry populations in southern New England. Bayesian clustering of AFLP genotypes and principal coordinate analysis distinguished B. t. var. atropurpurea genotypes from 85 plants representing five invasive populations. While a single fetal plant resembled B. t. var. atropurpurea phenotypically and fell within the same genetic cluster, all other naturalized plants sampled were genetically distinct from the purple-leaved genotypes. Seven plants from two different sites possessed morphology consistent with Berberis vulgaris (common barberry) or B. xottawensis (B. thunbergii x B. vulgaris). Genetic analysis placed these plants in two clusters separate from B. thunbergii. Although the Bayesian analysis indicated some introgression of B. t. var. atropurpurea and B. vulgaris, these genotypes have had limited influence on extant feral populations of B. thunbergii. Key words: AFLP; Bayesian analysis; Berberidaceae; Berberis thumbergii; Berberis thunbergii var. atropurpurea: invasive plants; molecular markers.

Tissue proliferation (TP) is characterized primarily by the formation of galls or tumors at the crown of container-grown rhododendrons that were initially propagated in vitro. In the cultivar 'Montego', TP-like symptoms are first observed in vitro as shoot clusters with small leaves and nodal tumors. In addition, unlike the normal in vitro non-TP (TP-) shoots, in vitro TP (TP+) shoots proliferate rapidly without the presence of the plant growth regulator cytokinin in the tissue culture medium. Comparisons of the anatomy of TP+ and TP- shoot tips showed that TP+ shoots had a less developed vascular system, longer cells in the pith and cortex, and altered internodal elongation at the shoot apex. In addition, TP+ axillary buds were abnormal in that they were displaced onto the stem above the leaf axil, and a small group of proliferating cells replaced the shell zone at the base of the bud. Initiation of tumor formation began with the expansion of this region of cell proliferation (RCP) and shoot growth from the abnormal axillary bud (tumor bud). Organization of the tumor bud and extension of the RCP characterized the further development of two types of tumors. In polar shoot tumors, shoot growth continued from the persistent tumor bud and the tumor at the base of the shoot remained small in size. The RCP extends downward to the vascular junction of the subtending leaf and the stem of the TP+ shoot. In nonpolar tumors, continuous de novo meristem formation led to the development of large tumors with or without shoots. The RCP is present throughout the tumor and is associated with de novo meristem formation. Comparisons to the anatomy of other tumor-like structures showed that TP tumors of Rhododendron 'Montego' are most similar to tobacco genetic tumors. Key words: de novo meristem; Ericaceae; region of cell proliferation; Rhododendron; tissue proliferation; tumor bud.

The extent of rejuvenation that occurs during in vitro culture and propagation of Betula was determined. Comparisons were made between half-sib seedlings and micropropagated, grafted, and cutting-propagated mature-phase birch plants grown under similar conditions. To measure relative levels of juvenility, three clones were examined at 1, 4, and 8 mo postpropagation, for differences in stem and leaf morphology and the presence or absence of reproductive structures. Numerous morphological indicators of phase change in Betula were identified. Micropropagated plants are not initially morphologically identical to conventionally propagated mature plants and display many features characteristic of seedlings. Micropropagated plants that exhibited juvenile morphology developed mature morphology more rapidly than did plants grown from seed. However, some mature-phase morphological characteristics did not return to micropropagated plants during the time frame of the study. Rejuvenation of Betula appears to occur during in vitro micropropagation, but the level of juvenility that is regained may not be equivalent to that of a seedling. Not all morphological indicators of phase change are affected equally by in vitro rejuvenation.

The pattern of protein production during rejuvenation of in vitro cultured Betula was determined. Comparisons were made between half-sib seedlings and micropropagated, grafted, and cutting-propagated mature-phase birch grown under similar conditions. Three clones were examined at 1, 4, and 8 mo postpropagation, for differences in total denatured protein and peroxidase and esterase isozymes. Polyacrylamide gel electrophoresis was employed to produce protein banding patterns representative of each type of plant at each time postpropagation. Evaluation of total denatured protein banding patterns indicated that micropropagated plants are initially more like seedlings than mature plants. Peroxidase and esterase isozyme analyses detected differences in isozyme activity and composition between the variously propagated plants and supported evidence provided from the denatured protein patterns. The type of plant part that is evaluated is critical in determining if isozyme banding patterns can be seen. Specific proteins or enzymes that mediate phase change in birch could not be detected consistently between clones or tissue types.

Tissue proliferation (TP) is characterized primarily by the formation of galls or tumors at the crown of container-grown rhododendrons that were initially propagated in vitro. In the cultivar 'Montego', TP-like symptoms are first observed in vitro as shoot clusters with small leaves and nodal tumors. In addition, unlike the normal in vitro non-TP (TP-) shoots, in vitro TP (TP+) shoots proliferate rapidly without the presence of the plant growth regulator cytokinin in the tissue culture medium. Comparisons of the anatomy of TP(+) and TP(-) shoot tips showed that TP(+) shoots had a less developed vascular system and altered internodal elongation at the shoot apex. In addition, TP(+) axillary buds were abnormal in that they were displaced onto the stem above the leaf axil, and a small group of proliferating cells replaced the shell zone at the base of the bud. Initiation of tumor formation began with the expansion of this region of cell proliferation (RCP) and shoot growth from the abnormal axillary bud (tumor bud). Organization of the tumor bud characterized two patterns of further tumor development. In polar shoot tumors, shoot growth continued from the persistent tumor bud and the tumor at base of the shoot remained small in size. In non-polar tumors, the tumor bud became dedifferentiated and de novo meristem formation led to the formation of large tumors with or without shoots. The RCP was a common feature in polar shoot tumors and in non-polar tumors.