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Michael S. Dosmann

Aconitum sinomontanum is a robust perennial monkshood native to China that shows promise as a cultivated ornamental. However, nothing has been reported about the germination requirements of the species, and little is known about the requirements of the genus as a whole. The objective of this study was to test the influence of stratification (moist prechilling) on germination of A. sinomontanum seeds. The seeds were from wild-collected plants of identical provenance growing at the Arnold Arboretum (Jamaica Plain, Mass.). After harvest and before stratification, seeds were stored dry at 38 °F (3.3 °C) and percentage germination was assessed after seeds were stratified, also at 38 °F, for 0, 21, 42, or 84 days. It is likely that stratification is required for seeds of this species to germinate, as unstratified seeds failed to germinate through the duration of the experiment (73 days). The highest level of germination (90.8%) was achieved after 84 days of stratification, and as length of stratification increased, so did percentage germination and indices of peak value and germination value. Days to maximum germination decreased with additional days of chilling. Growers wishing to germinate seed of this species should stratify seed for 3 months to achieve the highest level of germination.

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Michael S. Dosmann

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Michael S. Dosmann and Peter Del Tredici

The 1980 Sino-American Botanical Expedition (SABE) to the Shennongjia Forest District, Hubei Province, China was the first botanical collecting trip by American scientists to that country since 1949. This collaborative venture with Chinese botanists yielded 2085 herbarium and 621 germplasm collections from the species-rich region. Our analysis tracked the fate of the SABE germplasm after its introduction to North America and represents one of the few case studies of its kind. Two hundred and fifty-eight of the original germplasm collections still survive and are in cultivation in at least one of 18 botanical institutions. Yet 115 of these (45%) are represented by a single accession growing in a single location, which suggests that the plant introduction process is more tenuous than is generally assumed. The scientific value of documented wild germplasm warrants that careful measures are in place to ensure that significant collections do not vanish. This case study outlines steps that can be taken throughout the introduction process (from propagation to distribution and follow-up) to prevent any such loss. In particular, the role of data sharing among institutions is highlighted as a means of identifying collection uniqueness, and assessing environmental adaptability and invasiveness.

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Michael S. Dosmann, Jeffery K. Iles and Mark P. Widrlechner

Germinability of two, half-sib seed sources of Cercidiphyllum japonicum Sieb. & Zucc. and one seed source of Cercidiphyllum magnificum (Nakai) Nakai was determined after not stratifying or stratifying seeds at 3.5 ± 0.5 °C (38.3 ± 0.9 °F) for 8 days followed by germination for 21 days at 25 °C (77 °F) in darkness or under a 15-hour photoperiod. Stratification was not required for germination, but increased germination percentage, peak value, and germination value for both species. Stratification increased germination of C. japonicum from 42% to 75%, and germination of C. magnificum from 12% to 24%. Light enhanced germination of nonstratified seeds of one source of C. japonicum and of C. magnificum from 34% to 52% and from 8% to 15%, respectively. Stratification improved germinability of both species and obviated any preexisting light requirements the seeds may have had.

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Jianhua Li, Michael S. Dosmann, Peter Del Tredici and Susyn Andrews

Sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA were used to examine genetic divergence of the two species of katsura [Cercidiphyllum japonicum Sieb. & Zucc. and Cercidiphyllum magnificum (Nakai) Nakai] and four clones of weeping katsura (`Amazing Grace', `Tidal Wave', `Pendulum', and `Morioka Weeping'), and to characterize the affinity of these weeping katsura to both species. Our results indicate that C. japonicum and C. magnificum are genetically distinct, supporting the recognition of them as separate species. Based on our DNA sequence data and morphological evidence, all weeping selections are phylogenetically derived from C. japonicum, not C. magnificum; nor are they of a hybrid origin between C. japonicum and C. magnificum. We propose the new cultivar-group Cercidiphyllum japonicum Weeping Group to include all katsura clones of weeping or pendulous habit, and recognize the cultivar epithet `Morioka Weeping' and its application to the excurrent and upright clone obtained from Japan and distributed in North America by the Arnold Arboretum.

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Michael S. Dosmann, William R. Graves and Jeffery K. Iles

The limited use of the katsura tree (Cercidiphyllum japonicum Sieb. & Zucc.) in the landscape may be due to its reputed, but uncharacterized, intolerance of drought. We examined the responses of katsura trees subjected to episodes of drought. Container-grown trees in a greenhouse were subjected to one of three irrigation treatments, each composed of four irrigation phases. Control plants were maintained under well-hydrated conditions in each phase. Plants in the multiple-drought treatment were subjected to two drought phases, each followed by a hydration phase. Plants in the single-drought treatment were exposed to an initial drought phase followed by three hydration phases. Trees avoided drought stress by drought-induced leaf abscission. Plants in the multiple- and single-drought treatments underwent a 63% and 34% reduction in leaf dry weight and a 60% and 31% reduction in leaf surface area, respectively. After leaf abscission, trees in the single-drought treatment recovered 112% of the lost leaf dry weight within 24 days. Leaf abscission and subsequent refoliation resulted in a temporary reduction in the leaf surface area: root dry weight ratio. After relief from drought, net assimilation rate and relative growth rate were maintained at least at the rates associated with plants in the control treatment. We conclude that katsura is a drought avoider that abscises leaves to reduce transpirational water loss. Although plants are capable of refoliation after water becomes available, to maintain the greatest ornamental value in the landscape, siting of katsura should be limited to areas not prone to drought.

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Brian E. Whipker, Shravan Dasoju, Michael S. Dosmann and Jeffery K. Iles

Double impatiens (Impatiens wallerana Hook.) `Blackberry Ice' (variegated-leaf) and `Purple Magic' (green-leaf) were grown on flood benches and irrigated with 50, 100, 200, or 300 mg·L-1 (ppm) N to study the effect of fertility on growth and development. Electrical conductivity (EC) levels at week 9 were similar for both cultivars at each fertilizer rate, except for the 100 mg·L-1 N where EC levels of `Blackberry Ice' were more than double those of `Purple Magic'. This indicated that the nutrient demands were less for `Blackberry Ice' and fertilization rates lower than 100 mg·L-1 N would be required. After nine weeks, plants grown with 100 mg·L-1 N had a 22% larger plant diameter than plants grown with either 50 or 200 mg·L-1 N. Fertilization rates of 50 mg·L-1 N resulted in plants which were covered with a higher percentage of blooms per unit of leaf area, but the plants were smaller. Plant tissue dry weight (leaf, bud, stem, and total) increased to the highest level at 100 mg·L-1 N, then decreased with further increases in fertilization rate. For maximum shoot growth with flood irrigation, growers should apply 100 mg·L-1 N when growing `Purple Magic' double impatiens and a fertilization rate between 50 and 100 mg·L-1 N for `Blackberry Ice'.