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  • Author or Editor: Hong Zhao x
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Overhead irrigation is widely used to water lettuce during commercial production in China but exerts potential water wastage and pollution. Subirrigation is thought as a water-saving, high-efficiency fertigation strategy. However, few studies have compared the nutritional value and nitrate content of lettuce grown using subirrigation with plants cultivated with overhead irrigation. Therefore, this study explored the ability of ebb-and-flow subirrigation strategies to produce high yields of a leafy lettuce (cultivar Biscia Rossa) with high nutritional value and low nitrate content. Lettuce plants were cultivated in an ebb-and-flow subirrigation system with different irrigation frequencies (every 2 or 3 days) and immersion times (5, 10 or 15 minutes); overhead irrigation was used as control. Ebb-and-flow subirrigation significantly enhanced several lettuce growth parameters, significantly increased the level of vitamin C, and significantly decreased the nitrate content of lettuce leaves compared with overhead irrigation. The optimal subirrigation strategy for lettuce production was irrigation every 3 days with 15 minutes immersion; this ebb-and-flow subirrigation protocol could potentially be used to save water and resources, improve yield and nutrient contents and reduce nitrate content in commercial greenhouse lettuce production.

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To explore the reasons for seed abortion in southern China fresh-eating jujube, improve its reproductive biology, and provide a theoretical basis for the crossbreeding of jujube, we carried out self-pollination and cross-pollination experiments with Ziziphus jujuba Mill. ‘Zhongqiusucui’ as the female parent. We observed the process of pollen tube growth in pistil and embryo development by fluorescence microscopy and paraffin section methods. The results show there were self- and cross-incompatibilities during pollination and fertilization, and there were no significant differences in pollen germination and pollen tube growth between self-pollination and cross-pollination. It took at least 4 hours for pollen and stigma to recognize each other, 6 hours for pollen to germinate on the stigma, and 12 hours for the pollen tube to penetrate the mastoid cells of the stigma. After 48 hours of pollination, the pollen tube reached one third of the style. The pollen tube remained stagnant 72 to 120 hours after pollination, and remained at one third of the stylar canal. Simultaneously, the pollen tubes on the stigma twisted and interacted with each other, and expanded into a spherical shape. A few pollen tubes reached the ovary and completed fertilization. However, some early globular embryos degenerated before forming into globular embryos and resulted in the formation of empty embryo sacs, which leads to seed abortion. In conclusion, the poor pollination and fertilization, and the blocked development of the embryo resulted in seed abortion in Z. jujuba ‘Zhongqiusucui’.

Open Access

A 920 bp fragment of the ACC oxidase gene promoter from tomato (LEACO1) was used to drive GUS gene expression. The LEACO1 0.92kb fragment contained two stress-responsive short motifs; a 10 bp TCA motif (5'-TCATCTTCTT-3') twice (allowing two substitutions) and an 8 bp element (5'-AA/TTTCAAA-3') once. The TCA motif is found in over 30 stress- and pathogen-inducible genes while the 8 bp element is necessary for ethylene-response in the carnation GST1 and the tomato E4 gene promoters. Previously in chrysanthemum, cytokinin regulation with LEACO1 0.92kb produced dramatic increases in lateral branching and bud initiation. Tobacco plants carrying LEACO1 0.92kb –GUS were used to examine the response of the LEACO1 0.92kb promoter to various hormones and hormone inhibitors. GUS activity in LEACO1 0.92kb –GUS plants was detected in leaves and stems, but not roots. High expression was detected in shoots with the apical bud intact, but GUS activity decreased with the apical bud removed. Applying IAA to the shoot apex after removing the apical bud, restored GUS activity. However, the IAA transport inhibitor TIBA reduced GUS activity in shoots with intact apical buds, and in IAA-treated shoots with excised buds. In shoots with excised apical buds, GUS activity increased when the ethylene precursor ACC was applied, but decreased in intact shoots when the ethylene biosynthesis inhibitor AOA was applied. These data suggest that auxins produced in the apical meristem are capable of regulating LEACO1 0.92kb activity, probably through auxin-induced ethylene biosynthetic pathway activity.

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Ethylene response factor (ERF) genes have been characterized in numerous plants, where they are associated with responses to biotic and abiotic stress. Modified atmosphere packaging (MAP) is an effective treatment to prevent lotus root browning. However, the possible relationship between ERF transcription factors and lotus root browning under MAP remains unexplored. In this study, the effects of phenol, phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) enzyme activities; and PPO, PAL, POD, and ERF gene expression on fresh-cut lotus root browning were studied with MAP. The expression pattern of ERF2/5 correlated highly with the degree of browning. It is suggested that NnERF2/5 can be used as an important candidate gene for the regulation of fresh-cut lotus root browning under MAP, and the correlation of each gene should be studied further.

Open Access

With the phase-out of methyl bromide due to its impact on ozone depletion, research has focused on developing alternative chemical and biologically based soil disinfestation methods. Anaerobic soil disinfestation (ASD) was developed to control plant-parasitic nematodes, weeds, and soilborne pathogens. However, whether farmers will adopt ASD methods on a large scale is unknown. This study evaluates the economic viability of using ASD in open-field, fresh-market tomato (Solanum lycopersicum) production, drawing on data from field experiments conducted in 2015 in Immokalee, FL, and Citra, FL. The experiment included three treatments: chemical soil fumigation (CSF), ASD1 [the standard ASD treatment with 1482 gal/acre molasses and 9 tons/acre composted poultry litter (CPL)], and ASD0.5 (the reduced rate ASD treatment with 741 gal/acre molasses and 4.5 tons/acre CPL). Results from the economic analysis show that ASD treatments require higher labor costs than CSF regarding land preparation and treatment application. However, yields from ASD treatments are higher than those resulting from CSF, and the improvement in yield was enough to offset the increased labor costs. Relative to CSF, ASD0.5, and ASD1 achieved additional net returns of $630.38/acre and $2770.13/acre, respectively, in Immokalee, FL. However, due to unexpected conditions unrelated to soil treatments, the net return of ASD1 was lower than that of CSF in Citra, FL. Breakeven analysis indicates that ASD treatments would remain favorable even with an increase in the molasses price. However, when the tomato price is low, ASD could potentially lose its advantage over CSF.

Open Access

Anaerobic soil disinfestation (ASD) is considered a promising sustainable alternative to chemical soil fumigation (CSF), and has been shown to be effective against soilborne diseases, plant-parasitic nematodes, and weeds in several crop production systems. Nevertheless, limited information is available on the effects of ASD on crop yield and quality. Therefore, a field study was conducted on fresh-market tomato (Solanum lycopersicum L.) in two different locations in Florida (Immokalee and Citra), to evaluate and compare the ASD and CSF performances on weed and nematodes control, and on fruit yield and quality. In Immokalee, Pic-Clor 60 (1,3-dichloropropene + chloropicrin) was used as the CSF, whereas in Citra, the CSF was Paldin™ [dimethyl disulfide (DMDS) + chloropicrin]. Anaerobic soil disinfestation treatments were applied using a mix of composted poultry litter (CPL) at the rate of 22 Mg·ha−1, and two rates of molasses [13.9 (ASD1) and 27.7 m3·ha−1 (ASD2)] as a carbon (C) source. In both locations, soil subjected to ASD reached highly anaerobic conditions, and cumulative soil anaerobiosis was 167% and 116% higher in ASD2 plots than in ASD1 plots, in Immokalee and Citra, respectively. In Immokalee, the CSF provided the most significant weed control, but ASD treatments also suppressed weeds enough to prevent an impact on yield. In Citra, all treatments, including the CSF, provided poor weed control relative to the Immokalee site. In both locations, the application of ASD provided a level of root-knot nematode (Meloidogyne sp.) control equivalent to, or more effective than the CSF. In Immokalee, ASD2 and ASD1 plots provided 26.7% and 19.7% higher total marketable yield as compared with CSF plots, respectively. However, in Citra, total marketable yield was unaffected by soil treatments. Tomato fruit quality parameters were not influenced by soil treatments, except for fruit firmness in Immokalee, which was significantly higher in fruits from ASD treatments than in those from CSF soil. Fruit mineral content was similar or higher in ASD plots as compared with CSF. In fresh-market tomato, ASD applied using a mixture of CPL and molasses may be a sustainable alternative to CSF for maintaining or even improving marketable yield and fruit quality.

Free access

Increasing environmental concerns and legislation in many states and in other countries require that we take a more comprehensive sustainable “best management” approach to production techniques in nursery and greenhouse operations. This is particularly important because these production facilities are typically intense users of resources that are applied to relatively small land areas. We have developed an online knowledge center to facilitate the implementation of more sustainable practices within the nursery and greenhouse industry. A web-based knowledge center provides the most cost-effective mechanism for information delivery, as our potential audiences are extremely diverse and widespread. We currently have a registered user database of over 450 educators, growers, and industry professionals, and undergraduate and graduate students. A gateway website provides an overview of the issues and the goals of the project. The associated knowledge center currently has 25 in-depth learning modules, designed in a Moodle learning management framework. These learning modules are designed to actively engage learners in topics on substrate, irrigation, surface water, and nutrient and crop health management, which are integral to formulating farm-specific strategies for more sustainable water and nutrient management practices. Additional modules provide assessment and implementation tools for irrigation audits, irrigation methods and technologies, and water and nutrient management planning. The instructional design of the learning modules was paramount because there can be multiple strategies to improve site-specific production practices, which often require an integration of knowledge from engineering, plant science, and plant pathology disciplines. The assessment and review of current practices, and the decision to change a practice, are often not linear, nor simple. All modules were designed with this process in mind, and include numerous resources [pictures, diagrams, case studies, and assessment tools (e.g., spreadsheets and example calculations)] to enable the learner to fully understand all of the options available and to think critically about his/her decisions. Sixteen of the modules were used to teach an intensive 400-level “Principles of Water and Nutrient Management” course at the University of Maryland during Spring 2008 and 2009. The water and nutrient management planning module also supports the nursery and greenhouse Farmer Training Certification program in Maryland. The Maryland Department of Agriculture provides continuing education credits for all consultants and growers who register and complete any module in the knowledge center. Although these learning resources were developed by faculty in the eastern region of the United States, much of the information is applicable to more widespread audiences.

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