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Meng Wei, Aijun Zhang, Hongmin Li, Zhonghou Tang and Xiaoguang Chen

Nitrogen (N) is an essential macronutrient limiting plant growth and quality of leaf-vegetable sweetpotato (Ipomoea batatas Lam). The objective of this study was to investigate the effects of N deficiency and re-supply on growth, physiology, and amino acids in sweetpotato. Two leaf-vegetable sweetpotato cultivars, Pushu 53 and Tainong 71, were subjected to three treatments in hydro-culture: 1) N sufficiency, 2) N deficiency, and 3) N deficiency and subsequently with N re-supply. Compared with N sufficiency, N deficiency caused a decrease in vine growth, carotenoid and chlorophyll content (Chlt), root viability, photosynthesis, and nitrate reductase (NR) activity in both cultivars, but to a great extent in Tainong 71. Whereas N deficiency increased root growth and glutamine synthetase (GS) activity in both cultivars, and the increase in ‘Tainong 71’ was more obvious. Re-supply of N recovered the vine growth, root viability, Chlt, photosynthesis, NR, and GS activity, to a greater extent for ‘Pushu 53’ than for ‘Tainong 71’. N deficiency significantly decreased essential amino acids, including lysine, phenylalanince, isoleucine, tryptophane, leucine, and valine contents and nonessential amino acids, consisting of glutamic acid, aspartic acid, glycine, argnine, and proline content in both cultivars. These results indicated that the light leaf color leafy sweetpotato ‘Tainong 71’ is sensitive to the N availability and the dark green leaf color ‘Pushu 53’ is more tolerant to low N, which appear to reflect the differential response of two cultivars to their different adaptability to N availability.

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Liping Zhang, Chen Shen, Jipeng Wei and Wenyan Han

6-Benzyladenine (6-BA) is a safe and efficient cytokinin. The adult tea plants of the cv. Longjing 43 were used in this study. The foliar portion of tea bushes were sprayed with different concentrations (50, 100, 200, or 400 mg·L−1) of 6-BA after heavy pruning, when three to four leaves grew out in late May. The effects of 6-BA application on the growth of the new shoots and lateral branches were quantified. After 5 months, treatments with 50, 100, 200, or 400 mg·L−1 6-BA suppressed plant height by 11.0%, 18.0%, 21.0%, or 22.0%, respectively; 6-BA at 100, 200, or 400 mg·L−1 decreased the number of lateral branches by 20.0%, 23.0%, or 18.0%, respectively. Meanwhile, treatments with 50, 200, or 400 mg·L−1 6-BA increased the length of lateral branches by 38.0%, 79.0%, or 81.0% respectively; 200 mg·L−1 6-BA increased the diameter of lateral branches by 8.0%. In addition, after 2 months, 50 or 200 mg·L−1 6-BA did not significantly affect the growth of functional leaves, 50, 100, or 200 mg·L−1 6-BA did not significantly affect photosynthetic rate (Pn) as compared with the control. Furthermore, 200 or 400 mg·L−1 6-BA significantly increased spring tea yield by 28.9% or 13.3%, respectively as compared with the control. In conclusion, 6-BA at the four concentrations promoted dwarfing and the formation of productive lateral branches and increased the spring yield, and 200 mg·L−1 6-BA exerted the best comprehensive effect.

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Jin-wei Zhang, Yi-xue Liu, Jin-ping Yu, Wei Zhang, Ya-qiong Xie and Ning-ning Ge

In the early Spring of 2015 and 2016, weed infestation surveys were conducted in areas of cool-season turfgrass Festuca arundinacea Schreb. at 23 sites within Tianjin municipality in northern China. The weed community within turfgrass areas comprised 37 weed species belonging to 14 families. Perennial weeds accounted for 45.9% of the total community of weed species, whereas annual or biennial weeds accounted for 54.1%. Asteraceae was the dominant family (43.2%), and the percentage of broadleaved weeds was 94.6%. Statistical analyses of the weed dominance index (integrating weed relative height and relative coverage) and relative abundance (integrating weed relative density, frequency, and uniformity) showed that the 10 most common weed species during the early spring were Ixeris polycephala Cass., Taraxacum mongolicum Hand.-Mazz., Inula japonica Thunb., Hemistepta lyrata Bge., Trigonotis pedunclaris (Trev.) Benth., Calystegia hederacea Wall., Lepidium apetalum Willd., Plantago asiatica L., Cirsium segetum Bge., and Ixeris sonchifolia Hance. Ixeris polycephala Cass. and T. mongolicum Hand.-Mazz were the most dominant and harmful weed species. Partial correlation analysis (PACA) indicated that the deterioration rate (percentage of bare soil or coverage of plants other than turfgrass) of the turfgrass area was significantly and positively correlated with the total dominance index [(TDI), an index to evaluate the weed infestation severity)] and that the soil organic matter (SOM) and salinity factors were negatively correlated with the TDI. Factors such as soil nutrient conditions (the contents of N, P, and K and the total N), soil physical properties (density and clay content), soil moisture, soil temperature, and soil pH did not correlate significantly with the TDI. We conclude that the deterioration rate was the most important factor influencing weed infestation in the early spring and that SOM and soil salinity might also be important factors. The results of this study can help turfgrass researchers and managers identify the most harmful weed species and integrate management strategies in areas of cool-season turfgrass F. arundinacea Schreb. during early spring in the Tianjin region, China.

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Jian-Feng Geng, Cheng-Song Zhu, Xiao-Wei Zhang, Yan Cheng, Yuan-Ming Zhang and Xi-Lin Hou

Brassica rapa L. ssp. chinensis (L.) Hanelt, known as nonheading chinese cabbage in China, is an important vegetable in eastern Asia and its genetic improvement requires a genetic linkage map. The first genetic linkage map of nonheading chinese cabbage using 112 doubled haploid lines derived from a released F1 hybrid cultivar Shulü between two lines SW-3 and Su-124 was constructed in this paper. One hundred thirty-eight molecular markers were mapped into 14 linkage groups. Among these markers, there were 77 sequence-related amplified polymorphism markers, 27 simple sequence repeat markers, 21 random amplification polymorphic DNA markers, and 13 intersimple sequence repeat markers. Chi-square tests showed that 54 markers are distorted from Mendelian segregation ratios, and the direction of the distortion is mainly toward the maternal parent SW-3. The distortion affects not only the estimation of genetic distance, but also the order of distorted markers on a same linkage group. Given a specific marker order, the authors proposed a multipoint approach to correct the linkage map in an unbiased manner in an F2 population while considering distorted, dominant, and missing markers. A new method was used to correct the linkage map in the doubled haploid population mentioned earlier considering new, distorted, and missing markers. The total length of the corrected linkage map was 1923.75 cM, with an average marker spacing of 15.52 cM. The map will facilitate selective breeding and mapping of quantitative trait loci.

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Lian-wei Qu, Gui-mei Xing, Juan-juan Chen, Jia-jun Lei and Yan-qiu Zhang

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Wanmei Jin, Qiang Zhang, Sunzhong Liu, Qinping Wei, Wanmei Jin, Zongming Cheng, Xiaohui Xue and Tingzhen Yang

Molecular markers are valuable tools in evaluating genetic diversity and fingerprinting plant germplasm. In this report, simple sequence repeat (SSR) markers were used for assessing genetic diversity in 41 dwarf and semidwarf and early flowering apple (Malus sp.) rootstocks. Sixty-two of 112 pairs of SSR primers generated multiple, scorable fragments. The total number of scored bands was 4138 with the polymorphic frequency ranging from 22.0% to 68.6% with a mean value of 58.5% in 737 alleles. The number of alleles per locus ranged from 6 to 19 with an average of 11.9 alleles. Polymorphic information content per locus was ranged from 0.176 to 0.885 with an average value of 0.606. These results suggested a complex genetic background and genetic diversity in these apple rootstocks. Based on three principal components and unweighted pair group mean average (UPGMA) of SSR data, the 41 apple rootstocks were divided into five groups. Group I contained M. xiaojinensis ‘Xiaojinhaitang'. Group II consisted of M. hupehensis var. pingyiensis ‘Pingyitiancha'. Group III contained M. baccata ‘Shandingzi' and its offspring. Group IV was composed of 16 apple rootstocks, including Malling and Malling Merton series from Great Britain; ‘Budagovski 9' from Russia; ‘Polish 22' from Poland; ‘Cornell-Geneva 24' from the United States; and ‘GM.256', ‘Nei Meng 11', ‘MD.001', ‘7734', and ‘7848' from China. Group V consisted of 16 Shao series rootstocks, which were offspring of M. honanensis × M. domestica ‘Ralls Genet'. This research suggests that the breeding can achieve best performance with more robust rootstock if crosses were performed among these five major groups of germplasms rather than within the major groups.

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Fan Zhang, Zi Wei, Peter Jeranyama, Carolyn DeMoranville and Harvey J.M. Hou

Numerous observations of yellow vine syndrome of cranberry have been reported from commercial cranberry growers. The molecular mechanism resulting in yellow vine syndrome is unknown. We have previously reported on the shading effect as an approach to explore the mechanisms of yellow vine formation and proposed photoinhibition as a possible cause. To compare the photosynthetic performance of yellow vine-affected and normal cranberry leaves, we conducted chlorophyll fluorescence analyses over 1 period of 1 day and 3 weeks, respectively. Both experimental data sets indicated that the maximum quantum efficiency of photosystem II, the size of the quinone pool, the numbers of reaction centers (RCs) per chlorophyll absorption, and the photosynthesis performance index of the yellow vine samples are substantially lower than those of normal cranberry leaves. These results are in line with the data of yellow vine leaves, having 26% to 28% less in chlorophyll than the normal leaves as measured by spectrometric and high-performance liquid chromatography analysis. We concluded that yellow vine syndrome is associated with poor photosynthetic activity and is likely becoming a threat for the long-term growth and crop production of cranberries.

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L.X. Zhang, W.C. Chang, Y.J. Wei, L. Liu and Y.P. Wang

Cryopreservation of pollen from two ginseng species —Panax ginseng L. and P. quinquefolium L.—was studied. Freezing anthers that served as pollen carriers to –40C before liquid N storage affected pollen viability little after liquid N storage. Anther moisture content affected pollen viability significantly when stored in liquid N. The ideal anther moisture content to carry pollen for liquid N storage was 32% to 26% for P. ginseng and 27% to 17% for P. quinquefolium. Viability of pollen from P. quinquefolium anthers with 25.3% moisture content changed little after 11 months of liquid N storage.

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Zi Wei, Peter Jeranyama, Fan Zhang, Carolyn DeMoranville and Harvey J.M. Hou

Yellow vine symptoms are often observed in cranberry bogs. To explore the mechanisms of the formation of yellow vine syndrome in cranberry leaves, the shade effect on the chlorophyll (Chl) content and photosynthetic activities in cranberry bogs were investigated by spectrometric, high-performance liquid chromatography (HPLC), and in vivo Chl fluorescence kinetics. Spectrometric and HPLC analyses revealed that the yellow vine leaves were associated with a 11% ± 5% and 14% ± 5% increase in Chl a/Chl b ratio after shading, respectively. The Chl a/Chl b ratio was the same in both types of leaves, suggesting the photosystem (PS) II organization remains invariant. The rise in chlorophyll content suggested that the number of reaction sites on PS II is increased in the shaded yellow vine leaves. The results of in vivo chlorophyll fluorescence analysis also indicated that the electron transport chain in the PS II is enhanced and that the size of the quinone pool is increased. In addition, the overall photosynthesis index is drastically improved by shading. These three lines of evidence imply that the shading of cranberry plants appeared to reduce the syndrome by improving the photosynthetic activity and increasing the chlorophyll content. The techniques presented here may be valuable for characterizing variations of plants by stress or disease.

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Yihui Cui, Peng Zhao, Hongqiang An, Nan Lv, Zifeng Zhang, Wei Pei and Wanjun Wang

To find the characteristics of somatic embryogenesis of orchids and elucidate the mechanism, we had previously established an efficient plant regeneration system via somatic embryogenesis in Dendrobium candidum Wall ex Lindl. In this study, a detailed cytological investigation was carried out on the initiation and developmental process of somatic embryogenesis. Based on our observations, the somatic embryogenesis in D. candidum originated from the transition of an embryonic callus cell to the initial somatic embryo cell, and the somatic embryos initiated from those cells. During the transition process, condensation and devacuolation successively occurred in the cytoplasm of the embryonic callus cells, giving rise to the formation of a typical initial somatic embryo cell with dense cytoplasm and a clear nucleus. One of the two pathways in somatic embryogenesis is the single-cell-derived somatic embryo which is generated from an inner initial somatic embryo cell in embryonic callus and develops into a globular somatic embryo in a way similar to zygotic embryogenesis and then keeps developing into a protocorm-like body (PLB). The other is a multiple-cell-derived somatic embryo which is generated from peripheral grouped initial somatic cells in embryonic calli and directly forms globular embryo or multicellular somatic proembryo, lacking the typical early stages of embryogenesis. Both pathways were observed in the somatic embryogenesis system, indicating that the culture system in D. candidum can be a useful tool for investigating the mechanisms underlying orchid embryogenesis.