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Jianhua Li, Suzanne Shoup, Jianhua Li and Thomas S. Elias

Intergeneric hybrids are generally rare; nevertheless, such putative hybrids need confirmation from other lines of evidence besides morphological intermediacy. In this study the authors used DNA sequences of nuclear and chloroplast genes to determine the hybrid identity of ×Chitalpa. Their results confirm that both ×Chitalpa tashkentensis `Pink Dawn' and ×C. tashkentensis `Morning Cloud' are the result of an Chilopsis linearis ×Catalpa sp. cross. However, Catalpa bignonioides does not seem to have participated in the cross, as speculated before. Different species of Catalpa may have been used as the paternal parent. ×C. tashkentensis `Morning Cloud' is the result of the C. linearis × C. speciosa cross, whereas the paternal parent of ×C. tashkentensis `Pink Dawn' may be a hybrid plant of C. ovata and C. speciosa.

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Peter Del Tredici and Jianhua Li

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Jianhua Li, Jeremy Ledger, Peter Del Tredici and Donglin Zhang

The identity of heath-leaved cypress is controversial. In this study nucleotide sequences of nuclear ribosomal DNA were used to identify heath-leaved cypress (Chamaecyparis `Ericoides') species. Sixteen individuals were sampled representing the five species of Chamaecyparis, `Ericoides', and four other genera of Cupressaceae (Cupressus, Fokienia, Juniperus, and Thuja). The results placed `Ericoides' unequivocally to Chamaecyparis thyoides, supporting a conclusion derived from wood anatomy. This study supports the usefulness and integrity of using molecular data to identify the genetic affinity of cultivars that are morphologically different from the parent species.

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Dongyan Hu, Zuoshuang Zhang, Donglin Zhang, Qixiang Zhang and Jianhua Li

Ornamental peach (Prunus persica (L.) Batsch) is a popular plant for urban landscapes and gardens. However, the genetic relationship among ornamental peach cultivars is unclear. In this report, a group of 51 ornamental peach taxa, originated from P. persica and P. davidiana (Carr.) Franch., has been studied using AFLPs. The samples were collected from China, Japan, and US. A total of 275 useful markers ranging in size from 75 to 500 base pairs were generated using six EcoRI/MseI AFLP primer pairs. Among them, 265 bands were polymorphic. Total markers for each taxon ranged from 90 to 140 with an average of 120. Two clades were apparent on the PAUP–UPGMA tree with P. davidiana forming an outgroup to P. persica, indicates that P. davidiana contributed less to the ornamental peach gene pools. Within P. persica clade, 18 out of 20 upright ornamental peach cultivars formed a clade, which indicated that cultivars with upright growth habit had close genetic relationship. Five dwarf cultivars were grouped to one clade, supported by 81% bootstrap value, indicating that they probably derived from a common gene pool. These results demonstrated that AFLP markers are powerful for determining genetic relationships in ornamental peach. The genetic relationships among ornamental cultivars established in this study could be useful in ornamental peach identification, conservation, and breeding.

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Stephanie Byard, Michael Wisniewski, Jianhua Li and Dale Karlson

Temperate woody plants have evolved two methods for coping with seasonal exposure to subzero temperatures. Supercooling is a freeze-avoidance strategy in which cells can avoid intracellular freezing below subzero temperatures. Nonsupercooling is a freeze-tolerance strategy in which the growth of extracellular ice crystals is promoted and intracellular water is withdrawn. Thus, nonsupercooling species have also evolved adaptations to tolerate intracellular dehydration, which results from the formation of extracellular ice. The goal of our study was to provide the first broad characterization of freezing response within two representative woody genera (Acer and Betula) in relation to the evolution of the freezing response trait. Although all of the examined Acer species (nine) exhibited xylem supercooling response, only five of 14 Betula species were identified as supercooling species. When the characterized freezing responses were overlaid onto a phylogenetic tree, the supercooling freezing response was revealed as an ancestral trait in Betula.

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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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Dongyan Hu, Donglin Zhang, Zuoshuang Zhang, Qixiang Zhang and Jianhua Li

Ornamental peach [Prunuspersica (L.) Batsch.] is a well-known ornamental plant for the garden. However, the genetic relationship among ornamental peach cultivars is not clear, which limits further studies of its molecular systematics and breeding. A group of 16 taxa of ornamental peach, originated from Prunuspersica and Prunusdavidiana (Carr.) Franch., had been studied using AFLPs and ISSRs. A total of 243 useful markers between 75 to 500 base pairs were generated from six EcoRI/MseI AFLP primer combinations (ACC/CAT, AGG/CAT, ACT/CAT, ACC/CTC, AGG/CTC, and ACT/CTC). The average readable bands were 41 per primer combination. Among them, 84% of the bands were polymorphic markers. A total of 132 useful markers between 300 to 1400 base pairs were generated from 10 ISSR primers (UBC818, UBC825, UBC834, UBC855, UBC817, UBC868, UBC845, UBC899, UBC860, and UBC836). The mean reliable bands were 14 per primer. Among them, 62% of the bands were polymorphic markers. Both methods generated very similar phenograms with consistent clades. From these results we concluded that AFLP and ISSR analysis had a great potential to identify ornamental peach cultivars and estimate their phylogeny. The application of these molecular techniques may elucidate the hierarchy of ornamental peach taxa.