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  • Author or Editor: William R. Graves x
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Morphological distinctions between sugar maples and black maples are not consistently evident, and molecular assessment of genetic diversity is lacking for these taxa. We examined restriction-site polymorphisms in the ndhA intron of the chloroplast DNA (cpDNA) in populations of sugar maples and black maples representing their zones of allopatry and sympatry in eastern North America. Restriction-site analysis of the ndhA intron after digestion with HinfI and Sau3AI yielded no polymorphisms. Restriction digestion of the ndhA intron with TaqI revealed two cpDNA haplotypes that were neither geographically localized nor taxon specific. Although testing additional accessions of sugar maples and black maples for cpDNA variation will further elucidate patterns of genetic variation, our initial results suggest that the taxa are either exchanging genes or share an ancestral cpDNA polymorphism.

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Knowing whether leguminous trees have the potential to nodulate after infection by rhizobial bacteria is important for managing nitrogen (N) applications during tree production and for culture in the landscape. Although 98% of studied species in the Papilionoideae nodulate, the nodulation status of two tree species in this subfamily is uncertain. Cladrastis kentukea (Dum.-Cours.) Rudd (American yellowwood) did not form nodules during inoculation studies in 1939 and 1992. Nodules were observed on mature Sophora japonica L. (Japanese pagodatree) in Japan and Hawaii in the 1940s, but compatible rhizobia reportedly isolated in Japan are no longer held in bacterial collections. Our objective was to verify further that American yellowwood does not nodulate and to confirm reports that Japanese pagodatree does nodulate. Rhizobia that infect many plant hosts, soil samples and rhizobial isolates from other Sophora spp., and soil samples from mature American yellowwood and Japanese pagodatree were used to inoculate 5-day-old seedlings of American yellowwood, Japanese pagodatree, and control species. Soil from indigenous and introduced trees in the continental United States, Hawaii, Japan, and China was used. Inoculated and uninoculated plants were grown for 7 weeks in sterile Leonard jars or clay pots containing perlite and irrigated with sterile, N-free Hoagland's solution. No inoculation treatment elicited nodulation of American yellowwood or Japanese pagodatree. Our results provide additional evidence that American yellowwood lacks that capacity to nodulate and cast further doubt on nodulation of Japanese pagodatree.

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Freeman maples (Acer × freemanii E. Murray) are marketed as stress-resistant alternatives to red maples (Acer rubrum L.), but few data from direct comparisons of these species are available. As a first step in comparing the stress resistance of red maple and Freeman maple, responses to drought were studied in Acer × freemanii `Autumn Fantasy', `Celebration', and `Marmo'. Plants grown from rooted cuttings were treated by withholding irrigation through four drought cycles of increasing severity that were separated by irrigation to container capacity. Drought reduced shoot dry mass, root dry mass, and height growth by 64%, 43%, and 79%, respectively, over all cultivars. Predawn leaf water potential was reduced by 1.16 MPa over all cultivars, and stomatal conductance data indicated water use was more conservative over all root-zone moisture contents after repeated cycles of drought. Specific mass of drought-stressed leaves increased by 25% for `Autumn Fantasy', and microscopy to determine leaf thickness and cellular anatomy is ongoing. `Autumn Fantasy' also had the lowest ratio of leaf surface area to xylem diameter, and `Autumn Fantasy' and `Celebration' had higher ratios of root to shoot mass than `Marmo'. Pressure-volume curve analysis revealed osmotic potential of drought-stressed plants at full turgor was 0.24 MPa more negative than controls, and droughted plants had a greater apoplastic water percentage than controls. Although osmotic adjustment during drought was similar among cultivars, differences in specific mass of leaves and in ratios of transpiring and conducting tissues suggest cultivars of Freeman maple vary in resistance to drought in the landscape.

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Can Carolina buckthorn (Rhamnuscaroliniana) persist north of its native habitat without becoming invasive? Its distribution (USDA zones 5b to 9b) suggests that genotypes vary in cold hardiness, and invasiveness of other Rhamnus sp. has been linked to unusually early budbreak each spring. Therefore, we investigated depth of cold hardiness and vernal budbreak of Carolina buckthorns from multiple provenances and made comparisons to the invasive common buckthorn (Rhamnus cathartica). Budbreak was recorded in Ames, Iowa, from 9 Apr. to 10 May 2002. Buds of common buckthorn broke earlier than those of Carolina buckthorn, and mulching plants of Carolina buckthorn hastened budbreak. Stem samples were collected in October, January, and April from a plot in Ames, Iowa (USDA zone 5a), of Carolina buckthorns from three provenances (Missouri, Ohio, and Texas) and of naturalized common buckthorns. A similar schedule was followed during the next winter, when two plot locations [Ames, Iowa, and New Franklin, Mo. (USDA zone 5b)], were compared, but Carolina buckthorns from only Missouri and Texas were sampled. Carolina buckthorn and common buckthorn survived midwinter temperatures as low as –21 °C and –24 °C, respectively. Provenance differences were minimal; Carolina buckthorns from Missouri were more hardy than those from Ohio and Texas only in April of the first winter. We conclude that its cold hardiness will permit use of Carolina buckthorn beyond where it is distributed in the southeastern United States. Delayed budbreak of Carolina buckthorn relative to that of common buckthorn may underscore the potential for Carolina buckthorn in regions with harsh winters and may lessen its potential to be as invasive as common buckthorn.

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Six red maple (Acer rubrum L.) and four Freeman maple (A. ×freemanii E. Murray) cultivars were compared for rooting of single-node stem cuttings and subsequent development of rooted cuttings. Cuttings were taken in May 1990 and 1991 and treated with either 3 or 8 g IBA/kg. Rooting after 4 weeks differed among cultivars, ranging from 22% for `Karpick' to 100% for `Schlesinger' over both years. Rooting scores, based on root counts and lengths, were highest for `Schlesinger' and lowest for `Scarlet Sentinel' and `Karpick'. IBA at 8 g·kg–1 resulted in better rooting than at 3 g·kg–1. Mean length of shoots formed on potted rooted cuttings was 22.6 cm for `Franksred', which initiated shoots on 100% of the cuttings that rooted. In contrast, <50% of `Armstrong', `Jeffersred', `Karpick', `Northwood', and `Scarlet Sentinel' rooted cuttings initiated shoots, and mean length of new shoots was <4 cm for these cultivars. The amount of leaf desiccation that occurred after removing cuttings from the propagation bench varied among cultivars, and the percentage of viable leaf surface area correlated positively with final root or shoot dry mass for all cultivars. Chemical name used: indole-3-butyric acid (IBA).

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Early nodulin genes, such as ENOD2, may be conserved and could function as molecular markers for nodulation. Many nodulating and nonnodulating legumes must be analyzed before the role of such genes in nodulation can be determined. Japanese pagodatree and American yellowwood are closely related, ornamental woody legumes. Unsubstantiated reports of nodulation in Japanese pagodatree require confirmation, and American yellowwood has not been observed to nodulate. We investigated the presence of putative ENOD2 genes in these species, and we are studying differential and temporal expression. Genomic DNA of Japanese pagodatree and primers, derived from proline-rich pentapeptide repeats of conserved ENOD2 sequences, were used to obtain a 555-bp PCR fragment. This cloned fragment was used as a probe for Southern and Northern hybridizations. Genomes of Japanese pagodatree and American yellowwood contained sequences that are similar to ENOD2 sequences in other legumes. Treatments with either cytokinin or an auxin transport inhibitor may induce expression of the putative ENOD2 genes. New data on the characteristics of nodulin genes in woody legumes will clarify the nature and evolution of nodulation in legumes and may have implications for developing sustainable nursery production protocols.

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A complete picture of legume nodulation has yet to be elucidated. Most studies of the molecular mechanisms responsible for nodule organogenesis have focused on herbaceous legumes. We investigated the presence of a putative ENOD2 gene and studied the temporal and organ-specific production of its transcripts in an ornamental woody legume, Amur maackia. Primers derived from proline-rich pentapeptide repeats of conserved ENOD2 sequences and the genomic DNA of Amur maackia were used to obtain a 543-bp PCR fragment. Southern and Northern blots were probed with this cloned fragment. The Amur maackia genome contained an ENOD2 sequence that is similar to sequences in other species. Expression of the putative ENOD2 gene was detected in roots, 4 days after rhizobial inoculation, but not in leaves or stems. New data on the characteristics of nodulin genes in woody legumes will be beneficial in clarifying the nature and evolution of nodulation in legumes and may have implications for developing sustainable nursery production protocols.

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Use of cultivars resistant to high soil temperature could improve the performance of urban trees. The objective of this project was to examine selections of red maple (Acer rubrum L. and A. x freemanii E. Murray) for genotypic differences in resistance to root-zone heat stress. Development of roots and shoots from rooted single-node cuttings of seven genotypes grown in solution culture was optimal at about 28C. Shoot extension stopped within 3 weeks and terminal buds formed on plants of all genotypes at 36C. In a second experiment, the influence of 34C root-zone temperature on development varied significantly among six genotypes. Formation of terminal buds at 34C was observed only on plants of cv. Morgan and cv. Red Sunset. The reduction in new dry matter at 34C compared to plants at 28C ranged from 21% for cv. Schlesinger to 69% for cv. Morgan. We conclude that genotypes of red maple differ in resistance to high root-zone temperature.

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Maackia amurensis Rupr. & Maxim. is a leguminous tree with potential for increased use in urban landscapes. Information on the nutrition of M. amurensis is limited. To our knowledge, modulation and N2 fixation have not been reported. Our objective was to examine M. amurensis for nodulation and N2 fixation. Soil samples were collected near legume trees at arboreta throughout the United States, with additional samples from Canada and China. Seedlings were grown for six weeks in a low-N, sterile medium and inoculated with soil samples. Upon harvest, small white nodules were found on the lateral and upper portions of the root systems. Bacteria were isolated from the larger nodules, subculture, and used to inoculate seedlings. Inoculated plants nodulated and fixed N2 as determined by the acetylene reduction assay. We conclude M. amurensis forms N2-fixing symbioses with Rhizobium.

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Maackia amurensis Rupr. & Maxim. is a leguminous tree with potential for increased use in urban landscapes. Information on the nutrition of M. amurensis is limited. To our knowledge, modulation and N2 fixation have not been reported. Our objective was to examine M. amurensis for nodulation and N2 fixation. Soil samples were collected near legume trees at arboreta throughout the United States, with additional samples from Canada and China. Seedlings were grown for six weeks in a low-N, sterile medium and inoculated with soil samples. Upon harvest, small white nodules were found on the lateral and upper portions of the root systems. Bacteria were isolated from the larger nodules, subculture, and used to inoculate seedlings. Inoculated plants nodulated and fixed N2 as determined by the acetylene reduction assay. We conclude M. amurensis forms N2-fixing symbioses with Rhizobium.

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