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Open access

Uttara Samarakoon, Jack Palmer, Peter Ling and James Altland

Yield reduction resulting from high temperatures and tipburn are common issues during the summer for hydroponically grown lettuce using the nutrient–film technique (NFT). We investigated the yield and degree of tipburn of lettuce ‘Red Butter’, ‘Green Butter’, and ‘Red Oakleaf’ of the Salanova® series under different-solution electrical conductivity (EC) and pH levels. We also quantified the effect of foliar spray application of calcium chloride (CaCl2) on the yield and degree of tipburn using the lettuce cultivar Green Butter. For the EC experiment, the plants were grown at four EC levels (1.4, 1.6, 1.8, or 2.0 mS·cm–1) and a constant pH of 5.8. For the pH experiment, the plants were grown at and four pH levels (5.8, 6.0, 6.2, or 6.4) and a constant EC of 1.8 mS·cm–1. For the foliar spray experiment, CaCl2 was applied 1 week after transplanting into NFT channels at three different concentrations: 0, 200, 400, or 800 mg·L calcium (Ca). During the EC trial, the maximum yields were observed at or more than 1.8 mS·cm–1 for ‘Green Butter’ (263 ± 14 g/head) and ‘Red Butter’ (202 ± 8 g), and more than 1.6 mS·cm–1 for ‘Red Oakleaf’ (183 ± 6 g). The yield of ‘Green Butter’ was 75 g less at 1.4 mS·cm–1 compared with 1.8 mS·cm–1. Tipburn symptoms were less at 1.4 mS·cm–1 for ‘Green Butter’ whereas other cultivars were not highly susceptible. In pH trials, the maximum yield for all cultivars was found at pH 6.0 and 6.2. There were no differences in tipburn symptoms among all pH levels. The foliar spray treatment, twice a week at 400 or 800 mg·L–1 Ca, provided improved tipburn control, as the tipburn symptoms were minimal and the impact on yield was minor compared with reducing EC. This series of experiments found evidence in proper EC and pH management for optimum yield and tipburn control in NFT lettuce grown in summer conditions.

Open access

Mingyue Bao, Minmin Liu, Qingxia Zhang, Tonglin Wang, Xia Sun and Jinguang Xu

Herbaceous peony (Paeonia lactiflora Pall.) is a well-known ornamental plant with abundant flower colors. However, our understanding of the underlying mechanisms of flower color formation is limited. In this study, a wild sample of herbaceous peony (collected from Heze, China) and eight cultivars with different colors were selected for experimental investigation. The Royal Horticultural Society Color Chart was used to determine flower color, and the anatomic structure; cell sap pH value; moisture content (MC); condensed tannin content (Ct); soluble sugar and soluble protein content of the petals; and content and composition of anthocyanin, flavonoids, and carotenoids in the petals were examined. 1) In the white, pinkish white, pale purple, purplish pink, and reddish purple cultivars, deeper color was associated with greater total amounts of anthocyanin (TA). Hypochromic effects were observed for kaempferol-7-O-glucoside (Km7G), myricetin-3-rhamnoside (My3R), and luteolin-7-O-glucoside (Lu7G). The accumulation of quercetin-3-O-glucoside (Qu3G) and lutein affected yellow color formation in the petals. 2) There are papillate epidermal cells in the petals of the wild P. lactiflora sample, ‘Lanyucangjin’, and ‘Dongjingnvlang’. 3) Cell sap pH and MC of the petals of white, pinkish white, pale purple, and purplish pink cultivars were greater than those of the purplish red and most of the reddish purple cultivars. 4) The Ct was greatest in the purplish red cultivars, whereas no condensed tannins were detected in the white, pinkish white, and pale purple cultivars. 5) There were no significant correlations among soluble sugar content, soluble protein content, and the other physiological indications.

Open access

Qing Shen, Hua Bian, Hai-yan Wei, Li Liao, Zhi-yong Wang, Xiao-yan Luo, Xi-peng Ding, Zhenbang Chen and Paul Raymer

Seashore paspalum (Paspalum vaginatum) is an important warm-season turfgrass distributed in tropical and coastal areas. It has excellent resistance to abiotic stresses, such as salinity, drought, and low temperature. However, the research on genetic diversity of local P. vaginatum collections from China is limited. In this study, the genetic diversity among 58 P. vaginatum accessions from four different provinces in China and four cultivars were assessed using simple sequence repeat (SSR) markers. The results indicated that a total of 45 alleles were detected by 19 polymorphic markers, with a range of 2 to 4 and an average of 2.4 alleles per marker. The genetic similarity coefficients between each pair of the 58 P. vaginatum accessions and four cultivars ranged from 0.51 to 1.00, with an average of 0.77. The range of variation of Shannon diversity index of each SSR marker was 0.047 to 1.075, with an average of 0.486. The polymorphic information content of each SSR marker varies from 0.016 to 0.577, with an average of 0.249. The results of cluster analysis and principal component analysis (PCA) showed that 58 P. vaginatum accessions and four cultivars were divided into four groups. These results provide the theoretical basis for the genetic diversity assessments and molecular marker–assisted breeding of P. vaginatum species.

Open access

Bernadine C. Strik, Amanda J. Davis, David R. Bryla and Scott T. Orr

A 2-year trial was established in Oct. 2016 in western Oregon to evaluate the effects of various in-row mulch treatments on the establishment of northern highbush blueberry (Vaccinium corymbosum L. ‘Duke’). The treatments included douglas fir [Pseudotsuga menziesii (Mirb.) Franco] sawdust, black weed mat (woven polypropylene groundcover), green weed mat, and sawdust covered with black or green weed mat. Soil temperature was unaffected by the color of the weed mat, but it was often higher during the day in beds with weed mat mulch than in those with sawdust alone or sawdust covered with weed mat. Black or green weed mat also resulted in higher canopy temperatures, particularly when sawdust was underneath the weed mat. Plant growth was mainly unaffected by the color of the weed mat, and the maximum depth of the root system was similar among the mulch treatments. However, plants grown with sawdust mulch, with or without weed mat, had a greater canopy width and volume in year 2, a wider root system in both years, and more dry weight (DW) in the crown in year 1 and in the whips in year 2 than those with weed mat alone. Furthermore, plants with weed mat over sawdust were taller in year 1 and had greater canopy cover and more DW in new wood in year 2 than those with sawdust alone, and they had a larger canopy, more root development, and greater DW in the crown, new and old wood, fruit, and pruning wood in one or both years than those with weed mat alone. Over the course of the 2 years of the study, the net gain in total plant DW was lowest when the plants were grown with black weed mat and highest when they were grown with black weed mat over sawdust. Although it was more expensive initially, the use of weed mat over sawdust resulted in more plant growth than weed mat alone due to the insulating properties of the sawdust, and it was more effective for weed control than using sawdust alone.

Open access

Haijie Dou, Genhua Niu, Mengmeng Gu and Joseph Masabni

Understanding the responses of plant growth and secondary metabolite synthesis to different light wavelengths is important for optimizing lighting conditions for vegetable production in indoor vertical farms. Basil (Ocimum basilicum) ‘Improved Genovese Compact’ (green leaf) and ‘Red Rubin’ (purple leaf), green mustard ‘Amara’ (Brassica carinata), red mustard ‘Red Giant’ (Brassica juncea), green kale ‘Siberian’ (Brassica napus var. pabularia), and red kale ‘Scarlet’ (Brassica oleracea), which are high-value and multifunctional culinary herbs and leafy greens, were used to characterize the effects of red (R), blue (B), and green (G) wavelengths on plant photosynthesis, morphology, biomass production, and secondary metabolites accumulation. Light quality treatments consisted of three R and B light combinations, R88B12 (the proportions of R and B wavelengths were 88% and 12%, respectively), R76B24, and R51B49, and two white light combinations, R44B12G44 (the proportions of R, B, and G wavelengths were 44%, 12%, and 44%, respectively) and R35B24G41. Experiments were conducted in a walk-in growth room with a photosynthetic photon flux density set at 224 μmol·m−2·s−1 and a 16-hour photoperiod. Results indicated that the net photosynthesis in purple basil and green kale were positively correlated with B proportions (BP), and that higher BP increased the relative chlorophyll concentration in purple basil and red kale. In contrast, higher BP suppressed stem elongation and leaf expansion and reduced shoot biomass in all tested species except red mustard. Higher BP increased phytochemical concentrations but decreased the total amounts of phytochemicals per plant. For all basil and brassica (Brassica sp.) cultivars, the inclusion of G wavelengths decreased shoot biomass compared with that of plants grown under R and B light combinations with similar BP. Inclusion of G wavelengths stimulated stem elongation in green basil and green mustard under 12% BP; whereas it suppressed stem elongation in purple basil, green kale, red kale, and green mustard under 24% BP. The effects on phytochemical accumulation were species-specific for the inclusion of G wavelengths. Considering biomass production, nutritional values, and working environment for growers, a white light with lower BP and G proportions is recommended for culinary herbs and Brassica leafy greens production at vertical farms.

Open access

Zhijun Zhang, Huaifeng Liu, Junli Sun, Songlin Yu, Wang He, Tianyuan Li and Zhao Baolong

The use of resistant rootstocks is an inevitable trend in the development and production of grapes (Vitis sp.). The present study analyzed differences in the metabolites in grape seeds of different rootstock combinations (1103P, 5C, SO4, 3309C, 140R, and control) grafted onto ‘Cabernet Sauvignon’ (CS) wine grape (Vitis vinifera) scions (control, CS/CS, self-rooted grafting vines) using liquid chromatography–mass spectrometry (LC-MS) and nontargeted metabolomic techniques. Principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), and orthogonal-partial least squares discriminant analysis identified 30 significant metabolites and 22 metabolic pathways in the seeds of CS that differed significantly from the control seeds. This study revealed that rootstocks influence metabolite concentrations and metabolic pathways (alanine–aspartate–glutamate pathway, arginine-proline pathway, and the tricarboxylic acid cycle) in the scion onto which they are grafted. The rootstocks increased the concentration of delphinidin-3-(6-acetylglucoside), peonidin 3-(6-p-coumarylglucoside), L-threonine, and D-tartaric in CS seeds. Appropriate rootstock combinations can be used to improve the quality of grape seeds by changing the concentrations of amino acids, organic acids, polyphenols, and vitamin B. This study provides a theoretical basis for selecting grape rootstocks and provides important insights for improving the quality of commercial products derived from grape seeds.

Open access

Jason D. Lattier and Ryan N. Contreras

Althea (Hibiscus syriacus) is an ornamental shrub prized for its winterhardiness, flower colors, and unique flower forms, including single-flowered and double-flowered types. Although floral traits are most important for breeders of althea, little is known about their segregation patterns. The objective of this study was to determine segregation patterns in flower color, including eyespot, among hybrid seedlings of elite taxa. Over 4 years, more than 3100 flowering seedlings were produced for observation of F1, F2, and backcross families. For each plant, data were collected including presence of eyespot and petal body color (CIEL*a*b*) using a colorimeter. Recessive testcrosses and χ2 analyses were performed among three taxa (‘Buddha Belly’, ‘Diana’, and White Chiffon®), and between this recessive group and a suite of colorful taxa. Self-pollination and intercrosses within homozygous dominant and homozygous recessive groups further confirmed their genotypes. Based on these results, we propose that eyespot is controlled by a single gene called spotless, named for the recessive allele that results in a complete elimination of color in flowers. Crosses that resulted in seedlings that all produced eyespots were observed to segregate for color in the petal body. Of these, one group produced white to blush pink petals, which was recessive to full color. Recessive testcrosses and χ2 analyses were performed among nine taxa exhibiting eyespots with white to blush petal bodies, and between taxa with full-color petal bodies. These testcrosses resulted in a putative homozygous dominant group composed mostly of blue and dark pink taxa, whereas the heterozygous group was composed mostly of pink taxa. Spotless taxa were also added to these two groups, suggesting an epistatic interaction with the spotless allele. Based on these results, we propose that petal body color is controlled by a single gene called geisha, named for the recessive allele that produces white to blush-pink petal bodies and dark red eyespot. This trait exhibits incomplete dominance and is under epistatic control by spotless. Geisha-type flowers lack pigment in the petal body, or exhibit a blush pink, likely produced by low levels of cyanidin, peonidin, and pelargonidin. The interaction and segregation of these two genes was confirmed in F1, F2, and backcross families from two crosses: Lil’ Kim™ × Blue Chiffon™ and Fiji™ × White Chiffon®. This study on segregation of flower color in H. syriacus contributes substantial and useful information on inheritance of color and will facilitate targeted breeding to improve this vibrant ornamental shrub.

Open access

Zhou Li, Yan Peng and Bingru Huang

Small molecules, including H2O2 and Ca, mediate stress signaling and drought tolerance in plants. The objective of this study was to determine whether improvement in drought tolerance by H2O2 and Ca were associated with the regulation of transcription factors and stress-protective genes in perennial grass species. Plants of creeping bentgrass (Agrostis stolonifera) were sprayed with water (control), H2O2 (9 mm), or CaCl2 (10 mm) and exposed to drought stress for 20 days in controlled-environment growth chambers. Foliar application of H2O2 or Ca led to significant improvement in drought tolerance of creeping bentgrass, as demonstrated by greater turf quality, leaf relative water content, chlorophyll content, photochemical efficiency, and cell membrane stability, as compared with the untreated control. The application of H2O2 and Ca resulted in significant up-regulation of genes in Ca signaling transduction pathways [Ca-dependent kinase 26 (CDPK26), mitogen-activated protein kinase 1 (MAPK1), and 14-3-3] and transcript factors (WRKY75 and MYB13). For genes encoding antioxidant enzymes, H2O2 mainly enhanced superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and dehydroascorbate reductase (DHAR) expression, while Ca primarily improved transcript levels of SOD, monodehydroascorbate reductase (MDHAR), and GR. In addition, heat shock protein 70 (HSP70), metallothionein 1 (MT1), and glutamine synthetase 2 (GS2) were also markedly up-regulated by H2O2 and Ca under drought stress. However, the transcript level of lipoxygenase 3 (LOX3) was significantly down-regulated by H2O2 and Ca under well-watered and drought conditions. These results imply that H2O2 and Ca commonly or differentially regulate genes expression in association with drought tolerance through activating Ca signaling pathway and regulating transcription factors and stress-protective genes expression, leading to the alleviation of lipid peroxidation, maintenance of correct protein folding and translocation, and enhancement of nitrogen metabolism under a prolonged period of drought stress in creeping bentgrass.

Open access

Jaysankar De, Bruna Bertoldi, Mohammad Jubair, Alan Gutierrez, Jeffery K. Brecht, Steven A. Sargent and Keith R. Schneider

Florida peaches (Prunus persica) typically are picked and placed in a cold room on the day of harvest, then packed and shipped the next day. This room cooling (RC) is slow, requiring ≈24 hours or more for the fruit to reach optimal temperature (6 to 7 °C). There is currently limited research on the effect of cooling practices on microbial quality of peaches, yet this study is essential for decision making in areas such as upgrading packing house facilities and the implementation of improved handling procedures. This research compared the efficacies of postharvest cooling by RC, forced-air cooling (FAC), and hydrocooling with sanitizer (HS) treatment of peaches to reduce their surface microbial population and to determine the effect on shelf life and microbial quality. Three trials for RC and two trials each for FAC and HS were performed. Following cooling, fruit were stored at 1 °C. The average aerobic plate count (APC) from field samples was 5.29 log cfu/peach, which remained unchanged after RC or FAC but was reduced significantly (P < 0.05) to 4.63 log cfu/peach after HS. The average yeast and mold counts (Y&M) from field samples (6.21 log cfu/peach) were reduced highly significantly (P < 0.001) to 4.05 log cfu/peach after HS. Hydrocooling significantly (P < 0.05) reduced the APC and Y&M counts from the peaches and showed promise in maintaining the microbiological quality of the fruit throughout storage. However, at the end of the 21-day storage period, there was no significant difference in APC or Y&M counts from peaches, irrespective of the cooling methods. Peaches that went through the hydrocooling process and were subsequently packed showed an increase (P < 0.05) in both APC and Y&M counts, while fruit that were not hydrocooled showed no such increase. Information obtained will be used to recommend the best temperature management practices for maintaining the postharvest quality of peaches. A detailed cost-benefit analysis of different cooling methods and the time interval between harvest and shipment are both necessary for a more conclusive recommendation.

Open access

Craig J. Frey, Xin Zhao, Jeffrey K. Brecht, Dustin M. Huff and Zachary E. Black

Although grower interest in high tunnel tomato (Solanum lycopersicum) production has increased in recent years, systematic high tunnel research conducted in humid, subtropical regions has been limited. The potential of tomato grafting to mitigate biotic and abiotic stresses makes it complementary to high-value production systems in high tunnels. In this 2-year study, grafted vs. nongrafted organic tomato production in high tunnels and open fields was investigated to determine possible synergistic effects of these two technologies. In 2016, high tunnels resulted in a significant increase of total and marketable yields, by 43% and 87%, respectively, over open field production. Grafting also significantly increased total and marketable yields over nongrafted plants by 34% and 42%, respectively. Cultivar effects demonstrated greater benefits with the implementation of high tunnel and grafting technologies for ‘Tribute’ (a beefsteak-type tomato) than for ‘Garden Gem’ (a plum-type tomato), as the increase in marketable yield was 33% greater for ‘Tribute’ in high tunnels and 45% greater for ‘Tribute’ with grafting. In 2017, a delayed effective transplanting date and the lack of high tunnel summer season extension produced results that were generally cultivar specific. While grafting increased the total yield of both cultivars (by 18%), marketable yield was increased by grafting only for ‘Tribute’ in high tunnels (by 42%). Additionally, high tunnels improved marketable yield of ‘Tribute’ by 129% but had no effect on ‘Garden Gem’. This demonstrated the consistent trend of the beefsteak-type tomato benefiting more from the combination of high tunnel and grafting technologies than the plum-type tomato. High tunnels reduced fruit decay and cracking by up to 71% compared with open field production. Stink bug (Pentatomidae) damage had the greatest impact on marketable yields each season, reaching 13% and 34% of total yields in 2016 and 2017, respectively, and was unaffected by high tunnel production or grafting. This study revealed the benefits of integrating high tunnel and grafting technologies for enhancing organic production of fresh-market tomato in the humid subtropics, and demonstrated more research is warranted to establish regional planting dates and further optimize this high-value cropping system.