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  • Author or Editor: Li-li Zhang x
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Excessive bicarbonate concentrations and high irrigation water pH affect the growth and appearance of nursery plants in southern Florida. A greenhouse experiment consisting of five nitrogen (N) rates of urea or nitric acid was conducted to evaluate the influence of N sources and rates in irrigation water on bicarbonate concentrations, medium pH, and growth and appearance of anthurium (Anthurium andraeanum Lind.) plants. Pot medium pH, dry weight, plant appearance and N uptake by plants were significantly affected by N rates in irrigation water amended with either liquid urea or nitric acid, but the differences between the two N sources were not significant. The optimum growth and the best appearance of anthurium were achieved when N was added to irrigation well water as either urea or nitric acid at a rate of 20 mg·L-1 (ppm) and an electrical conductivity in a range of 0.36 to 0.42 dS·m-1 Nitrogen rates at 80 and 120 mg·L-1 induced adverse plant growth because of the greater salinity of the solutions and the lower pH of the medium.

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Kalmia latifolia L. (mountain laurel), a member of Ericaceae, is a beautiful ornamental shrub native to the eastern United States. The plant is not common in the southeastern United States landscapes because of the limited heat tolerance of most commercial cultivars. Breeding of heat-tolerant cultivars can be achieved by cross hybridization, but is often challenged by low germination percentage, long germination time, and potential abortion of cross-hybridized seeds. We used in vitro seed germination to enhance germination and shorten germination time and investigated the appropriate collecting time, optimal basal medium, and pH for this approach. Collecting time affected in vitro seed germination, with more mature hybrid seeds [collected 4–5 months after pollination (MAP)] having higher germination rate (90% in 4 weeks) than the less mature seeds collected in 2 MAP (20% in 7 weeks). Seedlings from the mature seeds also produced two true leaves on average after 8 weeks of culture, whereas seedlings from the less mature seeds had no true leaves. Woody Plant Medium (WPM) better enhanced in vitro seed germination compared with Murashige and Skoog (MS) or Gamborg’s B5 (B5) medium. WPM yielded higher germination (98%) than MS (90%) and significantly greater total leaf area per seedling (67 mm3) than MS (50 mm3) and B5 (52 mm3) for seeds of ‘Firecracker’ × ‘Snowdrift’. Similar effects had been observed on seeds from ‘Little Linda’ × ‘Starburst’ and ‘Pristine’ × ‘Peppermint’. The pH ranging from 4.2 to 5.4 did not affect seed germination and seedling development of mountain laurel hybrids. Our protocol enabled early collection of mountain laurel hybrid seeds 1 month before their full maturation and permitted seeds to germinate in 4 weeks on WPM, which shortened the period from crossing to the seedling stage from up to 15 to 6 months and enhanced germination percentage from 30% to more than 90% compared with traditional seed germination. This protocol should be applied to promote the breeding and selection of new mountain laurel cultivars for the southeastern United States landscapes.

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Four papaya (Carica papaya L.) lines that may have commercial value were surveyed for variability in ripening characteristics. Skin and flesh yellowing, fruit softening, respiration rate, and ethylene production were compared. Skin yellowing and flesh softening followed a similar sigmoid pattern for all lines. However, the temporal relationship between skin yellowing and flesh softening differed among the lines. Fruit from lines RL-1-3 and RL-1-12 did not begin to soften until the skin was 80% yellow, compared to 40% yellow for the commercial cultivars Kapoho and Sunrise. Fruit from RL-1-3 and RL-1-12 took 12 and 16 days, respectively, to reach 100% yellow from color break, which was two to three times as long as that of `Kapoho' and `Sunrise' at 22C. All lines showed typical climacteric respiration and ethylene patterns. The time between the start of skin yellowing and the rise in respiration varied from ≈2 days in `Kapoho' and `Sunrise' to ≈4 days in line RL-1-3 and 8 days in line RL-1-12. The respiratory peak was greatly reduced in RL-1-12. The patterns of softening in lines RL-1-3 and RL-1-12 differed from `Kapoho' and `Sunrise': RL-1-3 softened slowly, but reached similar firmness values to other lines 4 days after 100% yellow skin color; RL-1-12 had a much slower rate of softening and the fruit were still firm 4 days after the fruit reached 100% yellow. The ripening patterns of line RL-1-3 and RL-1-12 could be useful in postharvest handling and provide material for studying the genetic control of fruit softening.

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Twenty-four representative melon varieties and six parental cultivars were examined in this study. Among 159 pairs of simple sequence repeat (SSR) primers, 18 SSR core primers with rich polymorphic information, a large number of genotypes, and the ability to distinguish different melon varieties were selected. A total of 113 genotypes were detected among the 30 experimental materials, with an average of 6.28 genotypes for each pair of primers. The polymorphic information content was on average 0.6807, ranging from 0.5618 to 0.7885. Specific bands of the primers for the 30 experimental materials were analyzed, and by combining different primer loci, all 30 varieties were identified. Unique barcodes for molecular identity cards for the 30 experimental materials were established using the fingerprints formed with this SSR marker system. Each variety has a unique identity card that can be applied for the registration of the newly bred varieties, the protection of breeders’ rights, and the authenticity of breeds after promulgation of the new Seed Law of the People’s Republic of China.

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Iris (Iris sp.) is a popular and widely planted herbaceous perennial. However, most iris species go dormant without any aesthetic quality for 5–6 months in the transition zone between the temperate and subtropical climates. To investigate the effects of species/cultivars, leaf shape, and air temperature conditions on the ability to stay green, 12 popular species and cultivars in the transition zone were evaluated. Iris tested included the following species: roof iris (I. tectorum), japanese iris (I. japonica), long leafed flag (I. halophila), yellow flag (I. pseudacorus), blood iris (I. sanguinea), japanese water iris (I. ensata), and small-flower iris (I. speculatrix) and the following cultivars: ‘Chinensis’ milky iris (I. lactea var. chinensis), ‘Bryce Leigh’ louisiana iris (I. hexagonae), ‘Black Swan’ german iris (I. germanica), ‘Careless Sally’ siberian iris (I. sibirica), and ‘Loyalty’ japanese water iris (I. ensata). We conducted a 2-year field study on mature iris populations and evaluated the percentage of green leaves during winter retention and spring recovery using a digital image analysis (DIA). Green period during this study was calculated using predicted sigmoid curves based on the percentage of green leaves. The present study revealed that iris species/cultivars and air temperatures had considerable influence on the duration of the green period. Both evergreen and deciduous iris phenotypes exist with three different leaf shapes, among which the average green period of fan-shaped leaf iris species and cultivars was the longest. Because there was no significant (P = 0.205) relationship between green period during this period and leaf lethal temperature (LT50), new cultivars with long green periods may be achieved without a simultaneous loss of cold tolerance in iris.

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Soil water deficit impacts cold acclimation and freezing tolerance in creeping bentgrass (Agrostis stolonifera L.), but the mechanisms underlying have not been well understood. The objectives of this study were to investigate the effects of deficit irrigation before and during cold acclimation on osmoprotectants, antioxidant metabolism, and freezing tolerance in creeping bentgrass. The grass was subjected to three-soil moisture levels: well-watered [100% container capacity (CC)], deficit irrigation induced-mild drought stress (60% CC), and severe drought stress (30% CC) for 35 days including 14 days at 24/20 °C (day/night) and then 21 days under cold acclimation treatment (2 °C) in growth chambers. Leaf proline and total soluble sugar (TSS) levels were higher in the grass under mild drought stress relative to that under severe drought stress. Superoxide (O2 −·), hydrogen peroxide (H2O2), and malondialdehyde (MDA) content were higher in the grass under severe drought relative to that under well-watered and mild drought stress at day 35. Mild drought stress increased catalase (CAT) and guaiacol peroxidase (POD) activity, induced new isoforms and increased band intensities of superoxide dismutase (SOD), CAT, and POD during cold acclimation (days 14 to 35). No differences in osmoprotectants, antioxidant metabolism, and freezing tolerance were found between mild drought and well-watered treatments. The results of this study suggest deficit irrigation-induced mild drought stress in late fall and winter could induce accumulation of osmoprotectants and improve antioxidant metabolism, and freezing tolerance, but severe drought stress could reduce freezing tolerance of creeping bentgrass in the region with limited precipitation.

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Rhododendron delavayi Franch. is an important ornamental plant and often plays a role in natural hybridization with other sympatric species in Rhododendron subgenus Hymenanthes. Fifteen microsatellite loci were developed and characterized in this species. The average allele number of these microsatellites was four per locus, ranging from three to six. The ranges of expected (HE ) and observed (HO ) heterozygosities were 0.0365 to 0.7091 and 0.0263 to 0.9512, respectively. Cross-species amplification in R. agastum and R. decorum showed that a subset of these markers holds promise for congeneric species study. These sets of markers are potentially useful to investigate the genetic structure and gene flow of R. delavayi and other congeneric species.

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Mountain laurel (Kalmia latifolia) is an outstanding ornamental shrub due to its attractive foliage and showy inflorescences. Breeding efforts have led to improved selections that have predominantly been developed and evaluated in the northeastern United States. Consequently, most cultivars have largely been dismissed as incompatible for the southeastern U.S. environmental conditions by nursery growers and consumers. This study was conducted over a 4-year period to evaluate 21 popular mountain laurel cultivars, primarily developed in the northeastern United States, for container and field performance in Georgia. All cultivars yielded considerable growth in the first year of container trials, indicating production of mountain laurel as a 1-year container crop is feasible. Cultivars displayed significantly different total growth index throughout the container trial. Fast-growing cultivars such as Bullseye and Ostbo Red yielded more than 100, 150, and 250 cm of growth index in 1, 2, and 4 years, respectively. Conversely, cultivars that grew slower, such as Firecracker and Tinkerbell, had less than 80, 115, and 180 cm in 1, 2, and 4 years, respectively. Cultivars were classified into five groups, using principal component analysis, that included dwarf habit with pink flower, dwarf habit with nonpink flower, nondwarf habit with green stem and white flower, nondwarf habit with pigment-patterned flower, and nondwarf habit with pink flower. In a field study, performance rating of 21 cultivars ranged from 2.0 to 4.8 (out of 5.0) in 2014 and from 2.0 to 5.0 in 2015. Ten cultivars that received the highest ratings over these 2 years were selected for a subsequent field trial in 2016. Cultivars showed overall decreased ratings (1.0–3.3) from the previous 2 years because of late spring planting. ‘Ostbo Red’, ‘Pristine’, and ‘Tinkerbell’ had higher performance ratings, more net growth, and less decrease in maximum quantum yield, which indicated suitable adaptation to southeastern U.S. environmental conditions. Nursery growers and consumers should benefit from regional cultivar trial information derived from this study. ‘Ostbo Red’, ‘Pristine’, and ‘Tinkerbell’ performed well across trials and therefore are recommended for southeastern U.S. landscapes based on superior container and field performance, leaf spot (caused by Mycosphaerella colorata) tolerance, and morphologic distinctions.

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Gas chromatography ion mobility spectrometry (GC-IMS) was used to detect the volatile organic compounds (VOCs) of Zheng5–5 sweet cherry fruits cultivar under three cultivation patterns [arched cover (PN), umbrella cover (SX), and open field (LD)]. VOCs were analyzed and compared using three-dimensional and two-dimensional top view visualization, fingerprint analysis, and principal component analysis (PCA). A total of 24 VOCs (including monomers and dimers) were detected in PN, SX, and LD, and 19 of them were finally identified, mainly alcohols, aldehydes, acids, esters, and ketones. The VOCs of PN, SX, and LD were similar but significantly different in content. The three compounds with the highest relative content were 2-hexen-1-olD, ethanol, and hexanalD, with ranges of 13.71% (LD) to 22.31% (PN), 13.02% (SX) to 21.27% (LD), and 8.22% (LD) to 16.66% (PN), respectively. Esters are the main components that form the sweet cherry fruit aroma, with a relative content of LD>PN>SX. According to the PCA, fruit samples of PN, SX, and LD can be clearly distinguished, indicating significant differences in VOCs under different cultivation modes. The GC-IMS visual plots of PN, SX, and LD agreed with the PCA results, and their combination was suitable for characterizing the VOCs of sweet cherry fruits under different cultivation patterns. This study can provide a reference for evaluating the flavor characteristics of sweet cherry fruits with different cultivation patterns.

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Fruit ripening is a complex process involving many physiological changes and the dynamic interplay between different phytohormones. In addition to ethylene, jasmonates (JAs) have also been demonstrated to play an important role in the regulation of fruit ripening. However, the mechanisms underlying the interaction between these two pathways during fruit ripening are unknown. In recent years, research has been conducted to illustrate the effects of JAs on the ethylene biosynthesis and signaling pathway, but little is known regarding the effects of ethylene on JA biosynthesis and the signaling pathway during fruit ripening. Herein, we aimed to evaluate the effects of ethylene on JA biosynthesis in ripening apple (Malus ×domestica) fruit and on the expression of key genes involved in the JA biosynthesis and the signaling pathway. For this purpose, we treated apple fruit with ethephon and 1-methylcyclopropene (1-MCP) at commercial maturity. Our data indicated that endogenous JA content and allene oxide synthase (AOS) activity were reduced by ethephon treatment at the early ripening stage, whereas they were enhanced by 1-MCP treatment at the late ripening stage. Quantitative real-time polymerase chain reaction (PCR) analysis revealed that the expression profiles of three AOS genes (MdAOS2, MdAOS3, and MdAOS5) and two lipoxygenase (LOX) genes (MdLOX22 and MdLOX28) showed similar trends with the change of AOS activity in all groups during fruit ripening. The expression of MdLOX21 and MdLOX23 was in accordance with the change of ethylene production on ripening, and it was positively regulated by ethylene, whereas the opposite effect was observed for MdLOX39 expression. The transcription of MdLOX310 and MdLOX61 appeared unaffected by ethylene during fruit ripening. Three jasmonate ZIM-domain (JAZ) genes (MdJAZ9, MdJAZ10, and MdJAZ18) were differentially upregulated by ethephon treatment whereas being downregulated by 1-MCP treatment during fruit ripening. Expression of MdJAZ13 and MdJAZ14 was downregulated at the early ripening stage by both treatments. Our results suggested regulating roles of ethylene on the JA biosynthesis and signaling pathway during fruit ripening and senescence.

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