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Pengpeng Duan, Ying Sun, Yuling Zhang, Qingfeng Fan, Na Yu, Xiuli Dang and Hongtao Zou

A greenhouse field experiment involving tomato (Solanum lycopersicum) was performed using different nitrogen (N) management regimes: sole application of differing rates of chemical N fertilizer (SC) (SC treatments: N0, N1, N2, and N3) and combined application of manure and chemical N fertilizer (MC) (MC treatments: MN0, MN1, MN2, and MN3). These were used to understand the relationship between comprehensive fruit composition, yield, and N fractions (soil mineral N; soil soluble organic N; soil microbial biomass N, and soil fixed ammonium) under greenhouse conditions. The results showed that the MC treatments significantly increased vitamin C and soluble sugar content compared with SC treatments. In addition, the MN2 treatment produced a high yield and had a positive effect on fruit composition. The N3 (563 kg N/ha) and MN3 (796 kg N/ha) treatments resulted in a high loss of N below the root zone (0–30 cm), consequently reducing N use efficiency. Soil mineral N, soil soluble organic N, and soil fixed ammonium tended to be higher during the first fruiting period, whereas soil microbial biomass N tended to be higher during the second fruiting period. MC treatments significantly increased the N fraction in the 0- to 30-cm soil layer; N fractions tended to be higher with the MN2 treatment. According to an optimum regression equation, soil fixed ammonium during the first fruiting period and soil microbial biomass N during the second fruiting period had a more significant influence on tomato yield and fruit composition. Overall, application MC at an appropriate rate (MN2: 608 kg N/ha) is a promising approach to achieving high yields and optimum taste, and it offers a more sustainable fertilizer management strategy compared with chemical N fertilization.

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Francesco Rossini, Roberto Ruggeri, Tiziano Celli, Francesco Maria Rogai, Ljiljana Kuzmanović and Michael D. Richardson

In the transition zone, warm-season grasses are often overseeded with diploid perennial ryegrass (Lolium perenne L., 2n = 2x = 14) to provide a temporary green surface for winter sporting activities. Because improved cultivars of perennial ryegrass will often persist into summer in overseeded turf, alternative cool-season grasses have been developed to facilitate more rapid transition back to the warm-season species. Limited information is available on these alternative species, especially with regard to their germination characteristics under shade and performance under limiting factors, such as low temperature and restricted photoperiod. Greenhouse and growth chamber studies were designed to test four alternative overseeding grasses in comparison with diploid perennial ryegrass, to verify their potential use in the artificial environment of modern stadiums. Meadow fescue (Festuca pratensis Huds.), tetraploid perennial ryegrass (Lolium perenne L., 2n = 4x = 28), annual ryegrass (Lolium multiflorum Lam.), and spreading diploid perennial ryegrass [Lolium perenne L. subsp. stoloniferum (C. Lawson) Wipff.] were tested. Six different shade treatments were used in the greenhouse study, including 30%, 50%, 70%, 90%, and 100% shade and a nonshaded control (0% shade). Germination was monitored daily over a 21-day period by counting and removing emerged seedlings. The experimental design for this study was a randomized complete block design, with four replications of each species and shade level for a total of 120 experimental units. In the growth chamber study, the same plant material was tested simulating optimal, suboptimal, and critical environmental conditions that can be potentially found within a modern sport facility. In the greenhouse study, the highest final germination was observed with annual ryegrass at 90% shade (98.7%), whereas the lowest for tetraploid perennial ryegrass at 30% shade (58.8%). Annual ryegrass was the fastest emerging species, whereas meadow fescue the slowest. In the growth chamber study, in comparison with perennial ryegrass, the following results may be summarized: 1) meadow fescue and tetraploid ryegrass showed coarser leaf texture, similar growth rates and Normalized Difference Vegetation Index (NDVI) value; 2) annual ryegrass had similar leaf texture, accelerated growth characteristics, and lower NDVI value; and 3) spreading perennial ryegrass displayed finer leaf texture, lower vertical growth, and similar NDVI value.

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Eric Hanson, Brent Crain and Joshua Moses

Red raspberry cultivars that produce fruit on current season canes (primocanes) can produce additional fruit the following year on floricanes. The primocane-fruiting raspberries ‘Himbo Top’, ‘Joan J’, and ‘Polka’ were grown organically in high tunnels and pruned to different floricane densities to determine the effects on fruit yield (primocane, floricane, total) and harvest times. Floricane densities were 0, 2.4, or 4.8 canes per meter of row length in 2015, and 0, 4.9, or 9.8 canes per meter in 2016 and 2017. Total yield (floricane plus primocane) was significantly greater with low floricane density (17 t·ha−1) or high density (19 t·ha−1) compared with no floricanes (12 t·ha−1). Floricane density did not affect primocane yield or harvest times. Primocanes of ‘Polka’ were taller when floricanes were present, but primocanes of other cultivars were unaffected. Results indicate that producing fruit on both primocanes and floricanes (double cropping) can improve sustainable overall yields.

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Kuan-Hung Lin, Shao-Bo Huang, Chun-Wei Wu and Yu-Sen Chang

Exogenous application of either salicylic acid (SA) or calcium chloride (CaCl2) to alleviate heat stress has been extensively studied. However, the effects of combined SA and CaCl2 treatment on the heat tolerance of poinsettia have been poorly studied. This study investigated the role of a foliar spray comprising SA and CaCl2 in managing heat tolerance of three poinsettia (Euphorbia pulcherrima Willd.) cultivars, Noel, Winter Rose (WR), and Ice Punch’ (IP). Plants were pretreated with SA, CaCl2, or combined SA and CaCl2 and then exposed to a temperature of 42 °C for 1 hour. Changes in the relative injury (RI) percentage, malondialdehyde (MDA) content, and antioxidant enzyme activities were determined. All plants were then placed in an environment-controlled greenhouse for 14 days and evaluated. Lateral bud sprouting (%), new leaf numbers, and phenotypic appearance were recorded. Results revealed that the three poinsettia cultivars varied in their appearance, morphological growth patterns, and ability to tolerate high-temperature stress. Plant growth of ‘Noel’ was more robust than that of ‘WR’ and ‘IP’, which were considerably affected by heat stress, resulting in brown, withered leaves and defoliation. In general, the effects of the combined application of SA and CaCl2 on heat-tolerant ‘Noel’ were superior to those of individual applications and no treatment (for control groups) in terms of the RI percentage, lateral bud sprouting (%), and appearance under heat stress. Application of combined SA and CaCl2 for ‘Noel’ plants was more beneficial for enhancing catalase activity and resulted in the effective alleviation of decreased malondialdehyde content under heat stress. Treatment including 200 μΜ SA and 10 mm CaCl2 may alleviate heat stress and may prove useful in breeding programs focused on improving poinsettia cultivars.

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Ninghang Wang, Chao Zhang, Sainan Bian, Pengjie Chang, Lingjuan Xuan, Lijie Fan, Qin Yu, Zhigao Liu, Cuihua Gu, Shouzhou Zhang, Yaling Wang and Yamei Shen

Magnolia (Magnoliaceae) is widely cultivated for its beauty; however, despite this, the components of the different flower colors in Magnolia have not been elucidated. In this study, the color parameters of 10 Magnolia petals with different colors were measured by the Royal Horticultural Society Color Chart (RHSCC) and a color reader CR-10. The composition and content of the flavonoids in the petals were analyzed by high-performance liquid chromatography coupled with diode array detection (HPLC-DAD) as well as HPLC with electrospray ionization and mass spectrometry (HPLC-ESI-MS2). All results showed that the 10 petals were divided into four color groups. Regarding the flavonoid composition, four types of anthocyanins, including Cyanidin-glucosyl-rhamnoside (Cy-GR), Cyanidin-glucosyl-rhamnosyl-glucoside (Cy-GRG), Peonidin-glucosyl-rhamnoside (Pn-GR), and Peonidin-glucosyl-rhamnosyl-glucoside (Pn-GRG), were identified, as well as 10 types of flavonols. The flavonols included isorhamnetin, quercetin, kaempferol, and their glycosides, which included rutinoside, rhamnose, and glucoside. Cyanidin and peonidin make Magnolia petals appear red-purple and purple, respectively, and the flavonols perform as evident auxiliary pigments, particularly quercetin. The Magnolia cultivar flower phenotypes sampled in this study differed by changes in their existing flavonoid content rather than by the appearance of new flavonoids. Consequently, this study provides a reference for further revealing the basis of Magnolia flower color and provides clues for color breeding.

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Min Wang, Wenrui Liu, Biao Jiang, Qingwu Peng, Xiaoming He, Zhaojun Liang and Yu’e Lin

Heat stress (HS) negatively influences plant development and growth, especially production and quality. Cucumber is a widely cultivated plant in the gourd family Cucurbitaceae that is often exposed to high temperatures during summer and protected cultivation. In this study, we performed whole-genome re-sequencing of two pools, one heat-tolerant and one heat-sensitive, of the F2 population derived from L-9 (heat-resistant) and A-16 (heat-sensitive). The genetic analysis showed that the heat resistance of L-9 cucumber seedlings was controlled by a single recessive gene. By combining bulked segregant analysis (BSA) technology, the crucial gene related to HS was preliminarily mapped to a 1.08-Mb region on chromosome 1. To fine-map the locus, Indel markers were designed according to the genomic sequence. Finally, the gene was narrowed to a 550-kb region flanked by two Indel markers, namely Indel-H90 and Indel-H224, that contained 56 candidate genes. Re-sequencing results indicated that 10 candidate genes among the 56 in the candidate region showed single base pair differences in the exons. Quantitative reverse-transcription polymerase chain reaction showed that 6 genes among the 10 candidate genes were significantly decreased when exposed to high temperatures. These results not only were useful for the isolation and characterization of the key genes involved in HS but also provided a basis for understanding the mechanism of heat tolerance regulation.

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Mozhgan Zangeneh and Hassan Salehi

There are many species of Narcissus in diverse areas of the world in natural or cultured form and there is no complete information about their genetic status, especially the relatedness within a species. Thus, the current study applied intersimple sequence repeat (ISSR) markers to estimate the genetic diversity of 31 accessions, including 30 accessions of Narcissus tazetta, collected from 16 regions of Iran and one known exotic narcissus species that is being cultivated in Iran, and identification of tolerant genotypes for deficit irrigation by evaluation of their morpho-physiological characteristics. Seventeen anchored ISSR primers from a total of 19 tested ISSR primer pairs were used and produced 206 bands of different sizes. The average percentage of polymorphic bands was 96.02%. The maximum resolving power (8.32), polymorphic information content average (0.44), and marker index values (5.61) were observed for the primers of 811, 828, and 811, respectively. The unweighted pair group method with arithmetic mean based on Jaccard’s coefficients was used to assign the genotypes to one of two major clusters. Both clusters were divided into two subclusters, with single and double flowers separating into subgroups. The results showed that ISSR markers can be used as a diagnostic tool to evaluate genetic variation in Narcissus genotypes and reveal their relationships. The results of screening study identified drought-tolerant accessions. They were clustered into two major groups: drought-tolerant accessions with single flowers and drought-sensitive accessions having double and semidouble flowers. The findings presented can be used in breeding programs for different Narcissus genotypes.

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Zhigang Ouyang, Huihui Duan, Lanfang Mi, Wei Hu, Jianmei Chen, Xingtao Li and Balian Zhong

In eukaryotic systems, messenger RNA regulations, including splicing, 3′-end formation, editing, localization, and translation, are achieved by different RNA-binding proteins and noncoding RNAs. The YTH domain is a newly identified RNA-binding domain that was identified by comparing its sequence with that of splicing factor YT521-B. Previous study showed that the YTH gene plays an important role in plant resistance to abiotic and biotic stress. In this study, 211 YTH genes were identified in 26 species that represent four major plant lineages. Phylogenetic analysis revealed that these genes could be divided into eight subgroups. All of the YTH genes contain a YT521 domain and have different structures. Ten YTH genes were identified in navel orange (Citrus sinensis). The expression profiles of these CitYTH genes were analyzed in different tissues and at different fruit developmental stages, and CitYTH genes displayed distinct expression patterns under heat, cold, salt, and drought stress. Furthermore, expression of the CitYTH genes in response to exogenous hormones was measured. Nuclear localization was also confirmed for five of the proteins encoded by these genes after transient expression in Nicotiana benthamiana cells. This study provides valuable information on the role of CitYTHs in the signaling pathways involved in environmental stress responses in Citrus.

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Suxiao Hao, Yanfen Lu, Jing Liu, Yufen Bu, Qi Chen, Nan Ma, Zhiqin Zhou and Yuncong Yao

Dwarfing rootstocks can improve the plant architecture of apple trees and increase production. Gibberellins (GAs) are crucial for plant growth and dwarfing traits. The receptor, GIBBERELLIN INSENSITIVE DWARF1 (GID1), plays an important role in the regulation pathway. However, the growth regulatory mechanism of GID1 in dwarf apple rootstock seedlings is not clear. In this study, we selected dwarf apple rootstock ‘SH6’ and its cross parents as materials to clone the GA receptor gene GID1c. There were two different sites in the alpha/beta hydrolase domain. The expression of GID1c in ‘SH6’ was lower than that in Malus domestica cv. Ralls Janet, with the decrease of GA content. We further conducted GA3 treatment and overexpression of GID1c in tissue culture seedlings of ‘SH6’, and the results showed that the expression of GID1c and biosynthesis genes increased and promoted the accumulation of hormone contents, which ultimately regulates the growth of ‘SH6’ dwarf apple rootstock seedlings. Our results suggest that GID1c may affect the plant architecture and dwarf traits of dwarfing rootstock and accelerate its application in orchards.

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William Garrett Owen

Perennial hibiscus (Hibiscus sp.) are popular summer-flowering plants that are grown in greenhouses or nurseries, where growers must optimize production inputs such as fertility to maximize plant growth and produce high-quality flowering crops. The objective of this study was to determine the optimum fertilizer concentrations, identify leaf tissue nutrient sufficiency ranges by chronological age, and to expand leaf tissue nutrient standards of Hibiscus hybrid L. (hibiscus) grown in soilless substrates during container production. Two cultivars of hibiscus (H. hybrid L. ‘Mocha Moon’ and ‘Starry Starry Night’) were grown under one of six constant liquid fertilizer concentrations [50, 75, 100, 200, 300, or 400 mg·L−1 nitrogen (N)] with a constant level of water-soluble micronutrient blend in a greenhouse. The fertilizer concentrations sufficient for optimal plant growth and development were determined by analyzing plant height, diameter, growth index (GI), primary shoot caliper (PSC), and total dry mass, and they were found to be 100–300 mg·L−1 N after an 8-week crop cycle. Recently, mature leaf tissue samples were collected and analyzed for elemental content of 12 nutrients at 2, 4, 6, and 8 weeks after transplant (WAT) from plants fertilized with 100–300 mg·L−1 N. An overall trend of increasing sufficient tissue concentration over time was observed for total N, phosphorus (P), calcium (Ca), sulfur (S), zinc (Zn), copper (Cu), and boron (B), whereas a decreasing trend was observed for potassium (K), iron (Fe), manganese (Mn), and aluminum (Al). For instance, at 2 WAT, total N ranged from 3.1% to 5.1% N and increased to a range of 4.2% to 4.7% N at 8 WAT. At 2 WAT, Fe and Mn ranged from 79.2 to 103.6 mg·L−1 Fe and 66.3–82.8 mg·L−1 Mn and decreased to ranges of 75.6–82.9 mg·L−1 Fe and 18.1–99.7 mg·L−1 Mn at 8 WAT, respectively. Optimal leaf tissue concentration sufficiency ranges determined in this scientifically-based study were narrower than previously reported survey values for the genera Hibiscus.