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Hao Wang and Mary Ann Rose

Nutrient uptake and allocation patterns of Forsythia ovata × europaea `Meadowlark' grown in a recirculating hydroponic system in the greenhouse were observed for 5 months. Dormant rooted cuttings were placed in the system on 8 May 1995. The nutrient solution supplied (in mg·L–1) 100 N, 48 P, 210 K, 30 Mg, 60 Ca, 117 SO4, 3 Fe, 0.5 Mn, 0.15 Zn, 0.15 Cu, 0.5 B, 0.1 Mo. Solutions were completely replaced every 2 weeks. Leaves, stems, and roots were harvested for dry weight and nutrient analysis at monthly intervals. Nitrogen uptake and dry-weight accumulation in the roots increased throughout the experiment, reaching a maximum in the fifth month (September). Nitrogen uptake and dry-weight accumulation of leaves and stems increased rapidly throughout the first 3 months, then leveled off. Whole-plant N recovery (N taken up/N in hydroponics system) reached a maximum (58%) between 6 July and 3 August. N recovery in the hydroponics system was about 10 times greater than what we observed in related experiments with woody plants in typical production environments, suggesting that there is potential for manipulating fertilization and cultural practices to increase fertilization efficiency in woody ornamentals. Nutrient recovery and accumulation patterns of P and K also will be presented.

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Mary Ann Rose and Hao Wang

Micronutrient supplements were applied to container rhododendron (Rhododendron L. × `Girards Scarlet' [Girard Evergreen Hybrid Group]) in three forms: uncoated micronutrient fertilizer; slow-release, NPK-plus-minors fertilizer; and biosolids compost (15% v/v). Control plants received no supplement. While all micronutrient treatments had significantly higher foliar Mn or Cu concentrations than controls 1 year after potting, they did not increase growth (dry weight) or plant quality. At 1, 3, and 12 months after potting, the compost treatment had significantly higher diethylenetriaminepentaacetic acid (DTPA)-extractable levels of Mn, Fe, and Zn in the medium. Only one micronutrient fertilizer treatment increased extractable micronutrient concentrations (Cu) on all testing dates. Correlations between medium-extractable and foliar micronutrient concentrations were low (r 2 < 0.30). Vigorous growth in the control treatment suggested that adequate levels of micronutrients were supplied by the pine bark-hardwood bark-peat-sand medium. September concentrations [ppm (mg·L-1)] as low as 2.0 Mn, 17.8 Fe, 0.3 Cu, 4.2 Zn, and 0.9 B in DTPA extracts produced acceptable growth in rhododendron through the following June.

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Mary Ann Rose, Mark Rose and Hao Wang

Fertilizer recommendations for woody ornamentals suggest applying nutrients in early spring at budbreak, and in fall at the time of leaf coloration or leaf abscission. Because plants lack functional leaves at those times, there would be minimal contributions from photosynthesis to active ion absorption or from transpiration to mass flow of ions in soil towards roots. Thus, we hypothesized that fertilizer efficiency also would be low at those times. To estimate N uptake efficiency, 15N-enriched fertilizer was applied to container linden trees at one of five times during the 1998 season: at budbreak, during active growth, after terminal bud-set, before leaf abscission, and during leaf abscission. Half of the plants received 15N-nitrate-enriched ammonium nitrate on each date, and half received 15N-ammonium-enriched ammonium nitrate. Treated plants were harvested 10 days after enriched fertilizer application (29 May, 6 July, 17 Aug., 28 Sept., and 16 Nov.). Patterns of uptake were not different between plants treated with 15N-ammonium- or 15N-nitrate-enriched fertilizer. In both cases, nitrogen recovery efficiencies at budbreak and leaf abscission were much lower than at other application times. Whole-plant recovery efficiency of 15N-nitrate-enriched ammonium nitrate was 10% at budbreak, 13% at leaf abscission, and ranged from 58% to 71% for the intervening times. Recovery of 15N-ammonium-enriched ammonium nitrate was 6% at budbreak, 24% at leaf abscission, and 42% to 56% for intervening times.

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Mary Ann Rose, Mark Rose and Hao Wang

Crabapple [Malus ×zumi (Rehd.) `Calocarpa'] and maple (Acer ×freemanii E. Murray `Jeffersred') trees were grown in containers from 22 June to 3 Oct. with three fertilizer concentrations (50, 100, and 200 mg·L-1 N) and two levels of moisture tension in the medium [low setpoint (moist) = 5 kPa and high setpoint (dry) = 18 kPa]. Whole-plant growth was enhanced more by minimizing water stress than by increasing fertilizer concentration. Shoot length and whole-plant dry weight were greater (>29% for crabapple and >90% for maple) in low tension treatments (low water stress) but were unaffected by fertilizer concentration. Moisture tension also had a dominant effect on dry-weight allocation to leaves, stems, and roots. In contrast, foliar nutrient concentrations increased with fertilizer concentration but were affected to a lesser degree by moisture tension. Seasonal patterns in biomass allocation were little affected by treatments; the largest proportions of leaf and root biomass accumulated during summer and fall, respectively.

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Tao Wang, Ruijie Hao, Huitang Pan, Tangren Cheng and Qixiang Zhang

Mei (Prunus mume) is widely cultivated in eastern Asia owing to its favored ornamental characteristics and its tolerance for low temperatures. Reverse transcription quantitative real-time polymerase chain reaction (qRT-PCR) is a widely used method for gene expression analysis, requiring carefully selected reference genes to ensure data reliability. The aim of this study was to identify and evaluate reference genes for qRT-PCR in mei. Ten candidate reference genes were chosen, and their expression levels were assessed by qRT-PCR in four sample sets: 1) flowering mei; 2) mei undergoing abiotic stress; 3) different genotypes of Prunus species; and 4) all mei samples. The stability and suitability of the candidate reference genes were validated using commercially available software. We found that protein phosphatase 2A-1 (PP2A-1) and PP2A-2 were suitable reference genes for flowering with ubiquitin-conjugating enzyme E2 (UBC) also being suitable for different genotypes of Prunus species. UBC and actin (ACT) were most stably expressed under abiotic stress. Finally, the expression of an AGAMOUS homolog of Arabidopsis thaliana (PmAG) and a putative homolog of Group 2 late embryogenesis abundant protein gene in A. thaliana (PmLEA) were assessed to allow comparisons between selected candidate reference genes, highlighting the importance of careful reference gene selection.

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Fengge Hao, Lirong Wang, Ke Cao, Xinwei Wang, Weichao Fang, Gengrui Zhu and Changwen Chen

Crown gall disease caused by Agrobacterium tumefaciens affects a wide range of horticultural plants, and has no effective treatment. During the evaluation of crown gall resistance of peach germplasm resources, we observed enhanced resistance to subsequent invasion that was activated by virulence of A. tumefaciens in two peach cultivars. To further verify the phenotype observed in field experiments, systemic acquired resistance (SAR)-related salicylic acid (SA) and PR1 genes were investigated. The levels of SA were elevated in two cultivars, and these high levels were maintained for 35 days postinoculation. Compared with mock-inoculated controls, eight of the 22 candidate PpPR1 genes in A. tumefaciens-inoculated samples were significantly upregulated and three were downregulated in response to inoculation with A. tumefaciens. These data suggested that SA-induced SAR was activated in two peach cultivars by virulent A. tumefaciens infection. In addition, the eight induced PpPR1 genes can be used as molecular markers in defense studies in peach.

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Xuhong Zhou, Xijun Mo, Yalian Jiang, Hao Zhang, Rongpei Yu, Lihua Wang, Jihua Wang and Suping Qu

The omission of second division gene (OSD1) gene plays a fundamental role in meiosis and is associated with 2n gamete formation in Arabidopsis thaliana. The objective of this work was to unravel the mechanisms leading to 2n pollen production, and isolate and analyze the expression patterns of OSD-like (OSDL) genes in carnation (Dianthus caryophyllus). We found an absence of the second meiotic division caused the formation of 2n pollen. Three homoeologous genes were cloned and labeled as OSDLa, OSDLb, and OSDLc in a diploid carnation. The cDNAs were 1180 bp for OSDLa, 1288 bp for OSDLb, and 971 bp for OSDLc. A strong similarity was found between the amino sequences of OSDLb and OSDLc. An evident feature of OSDLs proteins is the presence of D-box and MR-tail domains; however, the GxEN/KEN-box domain, which is distinct among the other plant proteins was absent. Quantitative real time polymerase chain reaction (qRT-PCR) analysis showed that OSDL genes maintain continuous expression in buds and other tissues. OSDLa has the highest expression in buds of 1.1–1.2 cm long (stage 2), and OSDLb has a high level of expression in buds of 0.9–1.0 cm long (stage 1) and stage 2 buds and ovary tissues in three carnation cultivars. The expression level of OSDLc was highest in ovaries. These expression patterns strongly suggest that OSDLs in carnation involve male meiosis and ovary development. These findings can have potential applications in fundamental polyploidization research and plant breeding programs in carnation.

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Xianqin Qiu, Hao Zhang, Hongying Jian, Qigang Wang, Ningning Zhou, Huijun Yan, Ting Zhang and Kaixue Tang

Roses are one of the economically most important groups of ornamental plants. The internal transcribed spacers (ITS) of the nuclear ribosomal DNA and the chloroplast gene matK were used to investigate the genetic diversity and genetic relationships among Rosa germplasm including 39 wild species, 21 old garden roses, and 29 modern cultivars. Three dendrograms based on ITS and matK clustering data indicated that 1) 39 wild genotypes were consistent with their classification into botanical sections with only a few exceptions; 2) most of the wild genotypes were separated from rose cultivars. However, three sections, Synstylae, Chinenses, and Rosa, that contributed to the modern roses generally gathered together with almost all old garden and modern roses on the molecular level; and 3) the relationships between cultivated roses as inferred by ITS and matK sequences do not correlate with horticultural groups. Results demonstrated that both sequence techniques can contribute to clarifying the genetic relationships of rose accessions and germplasm conservation to enhance the ornamental and economic value of rose.

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Ting Zhou, Hao Jiang, Donglin Zhang, Junjun Fan, Long Zhang, Guibin Wang, Wangxiang Zhang and Fuliang Cao

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Junjun Fan, Wangxiang Zhang, Donglin Zhang, Ting Zhou, Hao Jiang, Guibin Wang and Fuliang Cao