Progress 10/01/02 to 09/30/04
Outputs
We have conducted studies on four Berberis thunbergii cultivars (AT=Atropurpurea; AU=Aurea; CP=Crimson Pygmy and RG=Rose Glow) and the green-leaved wild type (WT) using landscape specimens. We have generated data on the fruit production, seed production, germination rates, seedling foliage color, seedling vigor/growth capacity and the ability to grow in shaded conditions. The average seed production of some popular purple-leaf cultivars (AT and RG) approximates or exceeds that demonstrated by WT barberry, while others (AU and CP) have significantly reduced seed production. To move beyond this work using landscape plants and a limited number of cultivars, a replicated planting of 45 barberry genotypes in total has been established at UConn. This planting will provide uniform growing conditions for all genotypes and will furnish each genotype with a single, homogeneous and diverse pollen reservoir. Preliminary fruit productivity data from the replicated planting showed
differences in fruit production from no fruiting to very heavy fruiting. Additional fruiting evaluations are planned for the next several years. In addition to use for studies on reproductive potential, this planting is serving as a germplasm bank for DNA fingerprinting activities. These findings indicate that some existing barberry cultivars fruit little or not at all and may not present an invasive risk. Seedlings derived from AT and RG were just as vigorous as those from WT, while those from AU and CP were less vigorous. Some of the most interesting observations thus far concern the foliage color of seedlings raised from cultivar seed. Some observers have long assumed that purple-leaf barberry forms present little invasive danger since they must produce predominately purple progeny and purple plants are rarely seen among naturalized populations. Ratios of green to purple seedlings vary widely, however, among specimens of the same cultivar. For example, some CP specimens may produce
80%-90% purple seedlings, while others produce less than 10% purple seedlings, with the remainder green. It appears that seedling foliage hue varies according to the proximity of other barberry cultivars in the landscape. For example, a RG specimen growing adjacent to other purple-leaf forms may produce over 85% purple seedlings due to cross-pollination, while a plant near green-leaved forms may produce less than 5% purple seedlings. In studying the effect of shade levels from 30% to 70% on barberry cultivar seedlings, we found that shade levels as high as 70% did not seriously hinder germination and growth. However, shading of 70% did alter expression of the purple foliage phenotype and made all genotypes appear green. This observation brings into question whether some feral barberry may be genetically purple, but do not produce visible pigment due to intensely shaded growing conditions.
Impacts
Japanese barberry (Berberis thunbergii) cultivars are popular and useful landscape shrubs that represent millions of dollars of value to the landscape and nursery industries. As species are evaluated for invasiveness, one question that must be addressed is the invasive potential of cultivars. If a species is documented as invasive, will cultivated varieties of that species be considered invasive as well? Current policy is ambiguous, in part, due to a lack of scientific information about the role of cultivars in invasive plant biology and ecology. Japanese barberry and its cultivars represent a model system to use to ascertain how horticultural genotypes contribute to plant invasions. The findings from this research will provide guidance to local, state and national authorities as they assess how cultivars will be treated in invasive plant decisions.
Publications
- Lehrer, J. M. and M. H. Brand. 2003. Seed production levels and seedling traits of Berberis thunbergii cultivars. Proc. Intl. Plant Prop. Soc. 53:472-476.
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Progress 01/01/03 to 12/31/03
Outputs
Thus far quantitative data has only been collected and processed for the cultivar seed/seedling evaluation. Of the major commercial cultivars studied, Rose Glow produced the highest estimated seed production relative to canopy volume at 3.9x10-4 seeds/cm3 followed by Atropurpurea at 2.9x10-4 seeds/cm3, Crimson Pygmy at 2.4x10-4 seeds/cm3 and Aurea at 1.1x10-4 seeds/cm3. As a control, wild type B. thunbergii produced 2.3x10-4 seeds/cm3, though this estimate may be low due to the shaded conditions under which naturalized Japanese barberry normally grows. While the average gross seed production of popular commercial cultivars varies widely from plant to plant of the same cultivar, some trends are evident. Large-growing purple-leaf cultivars such as B. thunbergii Atropurpurea and Rose Glow on average produce greater than 1000 seeds per plant, a level comparable to or greater than wild type Japanese barberry. The yellow-leaf Aurea and the dwarf purple-leaf Crimson Pygmy
produce significantly fewer seeds on average. The foliage color of seedlings derived from popular Japanese barberry cultivars varies widely as measured by the ratio of green and purple seedlings. While some accessions of Atropurpurea, Rose Glow and Crimson Pygmy produced large percentages of purple-leaf seedlings (80%-90%) with the remainder green, other specimens produced predominately green seedlings. As a result, on average these cultivars produced no more than 50% purple seedlings. Wild type Japanese barberry produces almost 100% green seedlings with only an occasional purple individual. The initial results of this study indicate that important commercial cultivars such as Atropurpurea and Rose Glow demonstrate levels of gross seed production and seed production per canopy volume that approximate or exceed the levels expressed by wild type naturalized B. thunbergii. The figures for Aurea and Crimson Pygmy are somewhat lower. While such findings suggest that these cultivars are not
without invasive potential, other factors not measured as part of this study may more accurately predict the invasive ability of these plants. Seeds derived from Atropurpurea, Crimson Pygmy and Rose Glow produce ratios of purple and green seedlings that differ widely from plant to plant. Empirical observations seem to indicate a relationship between these ratios and the proximity of other Japanese barberry to the mother plant. For example, seed collected from a specimen of Atropurpurea growing immediately adjacent to plants of Rose Glow and Crimson Pygmy may produce greater than 80% purple seedlings, while a specimen of Rose Glow growing in isolation may produce greater than 90% green seedlings. These observations indicate that cross-pollination plays an important role in barberry seedling traits. It is clear that purple-leaf Japanese barberry cultivars can produce large numbers of green seedlings that may be indistinguishable from those derived from invasive B. thunbergii
populations.
Impacts
Japanese barberry (Berberis thunbergii) cultivars are popular and useful landscape shrubs that represent millions of dollars of value to the landscape and nursery industries. As species are evaluated for invasiveness, one question that must be addressed is the invasive potential of cultivars. If a species is documented as invasive, will cultivated varieties of that species be considered invasive as well? Current policy is ambiguous, in part, due to a lack of scientific information about the role of cultivars in invasive plant biology and ecology. The findings from this research will provide guidance to local, state and national authorities as they assess how cultivars will be treated in invasive plant decisions.
Publications
- Lehrer, J. M. and M. H. Brand. 2003. Horticultural strategies to counter invasive Japanese barberry (Berberis thunbergii). HortScience 38:757.
- Lehrer, J. M. and M. H. Brand. 2004. Seed viability and seed production levels in Berberis cultivars. Proc. Intl. Plant Prop. Soc. (in press).
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