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Dongyan Hu and Ralph Scorza

Since the first report of the ‘A72’ semidwarf peach [Prunus persica (L.) Batsch] tree in 1975, no new information has become available on this genotype. We evaluated the growth habit and verified the inheritance of ‘A72’ in a population of 220 progeny derived from self-pollination. Detailed tree and branch measurements revealed a unique forked-branch (FBR) character of the ‘A72’ (Nn) phenotype. The progeny segregated into 1 NN:2 Nn:1 nn. NN trees were indistinguishable from standard peach trees, Nn were FBR, and nn were dwarf. Hybrids between ‘A72’ and columnar (brbr) peach trees confirmed that FBR is inherited as a monogenic trait that appears to express incomplete dominance. ‘A72’ (Nn) trees were later blooming than sibling NN trees. The relationship (linkage or pleiotropy) between the growth habit of ‘A72’ and late bloom is not known. The structure of ‘A72’ trees presents new opportunities to breeder/geneticists, physiologists, and horticulturists to further explore the plasticity of peach tree growth and architecture that can be achieved through breeding. Applications of the ‘A72’ growth habit for commercial fruit production and as an ornamental, particularly in the dwarf form (nn) and in combination with the columnar tree (brbr) form, present opportunities that await exploration.

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Donglin Zhang, Hongwen Huang and Dongyan Hu*

Horticultural plants include fruit, vegetable, ornamental, turf, medicinal, beverage, spice, and other economic species. Although these plants originally derive from wild populations and play a vital role in our daily life, their importance on protecting biodiversity has not been addressed. With tremendous driving force of their monetary value, farmers, gardeners, breeders, and researchers have domesticated, selected, and bred many new horticultural crops, which ultimately increase biological diversity in cultivated plant communities. Both morphological and molecular data from 90 accessions of cultivated Cephalotaxus and 48 accessions of cultivated Chamaecyparis thyoides demonstrated their wide range of morphological differences and more than 43% of genetic dissimilarity coefficients. In US alone, one new cultivar of Loropetalum chinense var. rubrum was released to the nursery industry every year since the first plant was introduced from Wuhan Botanical Garden in 1983. Obviously, human activities rapidly accelerate evolutions. To preserve and reproduce new and rare taxa, regeneration of these plants is challenging. Rooting of Magnolia grandiflora stem cuttings, overcoming Cephalotaxus seed dormancy, experimenting Pinus strobus embryogenesis, and overwintering Stewartia cuttings should be applied for reproduction studies of unusual horticultural clones. For plants that could not be regenerated with today's propagation methods, their seeds, tissues, pollen, and embryos should be preserved as some USDA labs do for heirloom horticultural crops. In the future, with aid of advanced science and technology, we should be able to regenerate those plants from preserved materials and increase biological diversity.

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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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Dongyan Hu*, Zuoshuang Zhang, Donglin Zhang and Qixiang Zhang

Ornamental peach (Prunus persica (L.) Batsch) is native to China. The ornamental value of peach is gaining popularity for its use in urban landscape and everyday gardens. However, the genetic relationship among ornamental peach cultivars is not clear, which limits the further studies of its molecular systematic. A sample of 51 cultivars of ornamental peach, originated from P. persica and Prunus davidiana, had been studied by using AFLPs. All samples were collected from China, Japan, and the US. A total of 275 useful markers between 75 to 500 base pairs were generated from 6 EcoRI/MseI AFLP primer combinations. Among them, 93% of bands were polymorphic markers. Total markers for each cultivar ranged form 90 to 140, and the average number of markers for each cultivar was 120. Two distinguished clad generated from PAUP-UPGMA tree. P. davidiana, as a species, was apparently an out-group to P. persica, which implied that P. davidiana was far away genetically from ornamental peach (P. persica). Within P. persica clad, 15 out of 17 upright ornamental peach cultivars in this study were grouped to one clad, which indicated cultivars that with upright growth habit had close genetic relationship. Five dwarf cultivars were grouped to one clad, with 81% bootstrap supported. The genetic relationships between these five dwarfs were much closer than any other cultivars, and showed that they probably derived from the similar gene pool. The results demonstrated that AFLP are powerful markers for revealing genetic relationships in ornamental peach. The genetic relationships among ornamental cultivars established in this study could help future ornamental peach germplasm identification, conservation, and new cultivars development.

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Ajay Nair, Donglin Zhang, John Smagula and Dongyan Hu

Stewartia pseudocamellia Maxim. (Japanese Stewartia), a member of Theaceae (tea family), is an excellent garden plant with ornamental features for all four seasons. Reproduction difficulty, however, limits its popularity. We conducted three experiments to ascertain the optimum conditions needed for rooting and subsequent overwintering of semihardwood Stewartia pseudocamellia cuttings. Cuttings were collected in July and prepared for rooting using two types of hormones (KIBA quick dip and Hormodin powder) and three media (Perlite + ProMix, Perlite + Perennial Mix, or Perlite + ProMix + Perennial Mix). Rooted cuttings were overwintered at four different temperatures. The best overwintering temperature was 5 °C, at which 65.6% of newly rooted cuttings survived. Temperatures lower than –12.2 °C were detrimental to the plants. Without cold treatment, only 21.9% of the rooted cuttings survived, which was three times lower than those that received 5 °C treatments. Plants rooted in Perlite + Perennial Mix had 61.8% overwintering survival, which is significantly higher than Perlite + ProMix. The quality of roots, indicated by total root length per cutting, was higher (104.3 cm) with Perlite + Perennial Mix, but not statistically significant. Cuttings treated with rooting hormones had higher rooting percentages (71.9% to 93.6%) as compared with the control (53%). For the same concentration (8000 mg·L−1), liquid (KIBA) and liquid + powder (KIBA + indole-3-butyric acid) rooting hormones resulted in better rooting percentages than powder (Hormodin) alone, although there was no statistical difference in rooting percentages among rooting hormone treatments. The best hormone for subsequent overwintering survival was the combination of quick dip (5000 mg·L−1 KIBA) and Hormodin #2 (0.3% a. i.; equivalent to 3000 mg·L−1). It resulted in 64.2% survival, significantly higher than for KIBA quick dip (8000 mg·L−1 a.i.) or Hormodin #3 (0.8% a. i.; equivalent to 8000 mg·L−1) alone. Our results suggest that reproduction (rooting and overwintering) of Stewartia was affected by many factors. We recommend rooting Stewartia in media that has good aeration and moderate water-holding capacity and overwintering them at ≈5 °C.

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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.