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Juan Carlos Álvarez-Hernández, Javier Zaragoza Castellanos-Ramos and Cesar Leobardo Aguirre-Mancilla

Grafting Carica papaya plants can have several benefits for productive, phytosanitary, and sexing purposes. However, the literature on the subject of papaya grafting is limited. The tongue approach and cleft grafting techniques seem to be the most adequate for C. papaya, but the quality of grafts depends on several factors. With the objective of developing and adapting a grafting method for papaya, experimental assays were carried out in the Valley of Apatzingan, Michoacan, Mexico. The physical condition of the seedlings was assessed, and the most advantageous time for grafting was determined based on the size and thickness of the stems. Three assays were then carried out. The first assay was a test of the tongue approach and cleft grafting techniques using two clamping devices. The second assay involved the same techniques with modifications and the addition of another treatment. In the third assay, the modified tongue approach grafting method was tested on three containers with papaya plants. Seedling vigor, graft survival, and graft quality were the recorded variables. The results indicated that unwanted tissue should be cut 6 days after grafting. The tongue approach grafting method using tape as the fastening device (T-T) yielded a graft survival of 80%. The modified tongue approach grafting method, in which the tongues were formed just below the stem-site cut and tape was used as the fastening device (M-T-Bc-T), yielded a graft survival of 90%. In the third assay, the previously described modified method, but with seedlings grown in plastic bags (M-T-Bc-T-B), yielded a graft survival of 92.5%. It can be concluded that the modified tongue approach grafting method with seedlings grown in plastic bags (M-T-Bc-T-B), is a reliable grafting method for papaya that does not require special handling conditions.

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Josue Ortega-Ortega, Francisco Arturo Ramírez-Ortega, Roberto Ruiz-Medrano and Beatriz Xoconostle-Cázares

Coffee is an important crop worldwide, grown on about 10 million hectares in tropical regions including Latin America, Africa, and Asia. The genus Coffea includes more than 100 species; most are diploid, except for C. arabica, which is allotetraploid and autogamous. The genetic diversity of commercial coffee is low, likely due to it being self-pollinating, in addition, the widespread propagation of few selected cultivars, such as Caturra, Bourbon, and Typica. One approach is the analysis of genome size in these cultivars as a proxy to study its genetic variability. In the present work, genome size of 16 cultivars was assessed through high-resolution flow cytometry (FCM). Nuclear DNA was analyzed using a modified procedure that uses propidium iodide (PI) and 4′,6′-diamino-2-phenylindole dihydrochloride hydrate (DAPI) staining. The C. arabica cultivars investigated possessed a nuclear DNA content ranging from 2.56 ± 0.016 pg for Typica, to 3.16 ± 0.033 pg for ICATU, which had the largest genome size. All cultivars measured using both fluorochromes had greater estimates with DAPI than PI. The proportion of the genome composed of guanosine and cytosine (GC%) among the cultivars evaluated in this study ranged from 37.03% to 39.22%. There are few studies of genome size by FCM of distinct important C. arabica cultivars, e.g., hybrids and artificial crosses. Thus, this work could be valuable for coffee breeding programs. The data presented here are intended to expand the genomic understanding of C. arabica and could link nuclear DNA content with evolutionary relationships such as diversification, hybridization and polyploidy.

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Azadeh Behrooz, Kourosh Vahdati, Farhad Rejali, Mahmoud Lotfi, Saadat Sarikhani and Charles Leslie

Drought stress is one of the main constraints limiting worldwide crop production. Arbuscular mycorrhizae (AM) and plant growth-promoting bacteria (PGPB) such as Azotobacter chroococcum and Azospirillium lipofrum have been shown to alleviate drought stress effects. Therefore, the interaction effect of AM fungi [Glomus mosseae, G. etunicatum, and a mix of these (G. mix), and PGPB bacteria (Azotobacter chroococcum + Azospirillium lipofrum)] was investigated in 1-year-old walnut seedlings (cv. Chandler) under normal and drought stress conditions. Drought stress reduced growth (plant height, root length, number of leaves, and fresh weight) and leaf nutrient content (N, P, and Zn) significantly of walnut plants. In contrast, proline, total soluble sugar, starch peroxidase enzyme activity, and total phenolic content of walnut leaves increased under this stress. Application of fungi or bacteria, and especially their simultaneous use, alleviated the negative effects of drought stress on walnut seedlings. AM fungi and PGPB increased significantly the content of some metabolites, including total phenolic content, proline level, peroxidase activity, total soluble sugar, and starch content as well as peroxidase enzyme activity. This led to an increase in walnut plant growth under the drought stress condition. Among AM fungi, G. etunicatum was more effective in reducing drought stress symptoms than either G. mosseae or the G. mix of fungi. In conclusion, use of G. etunicatum, along with PGPB, can reduce negative effects of drought stress on walnut seedlings.

Open access

Abigail R. Debner, Harlene Hatterman-Valenti and Fumiomi Takeda

Outdoor production of floricane-fruiting (FF) blackberry (Rubus subgenus Rubus) is problematic in the Northern Great Plains region of the United States because cane injury and plant death will occur from exposure to temperatures −15 °C and colder. An annual FF blackberry production system using hardwood floricane cuttings would overcome some of the existing limitations of traditional production methods. Several experiments were performed to induce adventitious root formation from one-node hardwood floricane blackberry cuttings taken in winter for the purpose of subsequent growth of a floral shoot. One-node hardwood cuttings of multiple blackberry cultivars (Apache, Arapaho, Kiowa, Osage, Ouachita, Siskiyou, and Triple Crown) were evaluated for rooting potential with and without auxin treatments. Root formation was virtually nonexistent for ‘Apache’, ‘Kiowa’, and ‘Triple Crown’ regardless of the auxin treatment. In general, lower auxin concentrations and the powder formulation produced more roots and had higher root ratings. However, rooting success of cuttings and plant development was low regardless of the rooting method used. Adventitious root production of one-node dormant hardwood FF blackberry cuttings for use in an annual production system had low success regardless of the cultivar, auxin application, rate, and formulation. The variable propagation success rates using single-node hardwood cuttings from ‘Apache’, ‘Arapaho’, ‘Kiowa’, ‘Osage’, ‘Ouachita’, ‘Siskiyou’, and ‘Triple Crown’ plants grown in containers in North Dakota suggested insufficient rooting success for the recommendation of this practice. Additionally, the results suggested these cultivars are not suitable using this method for an annual production system or as a means for large-scale propagation. Although this approach to developing plants from cuttings is of great interest, without a more effective FF blackberry cutting rooting method that can progress through fruit production, an annual blackberry production system in the Northern Great Plains region of the United States is unlikely.

Open access

Mitchell Eicher-Sodo, Robert Gordon and Youbin Zheng

Hydrogen peroxide (H2O2) is an oxidizing agent used to disinfect recirculated irrigation water during the production of organic crops under controlled environmental systems (e.g., greenhouses). To characterize the phytotoxic effects and define a concentration threshold for H2O2, three microgreen species [arugula (Brassica eruca ssp. sativa), radish (Raphanus sativus), and sunflower (Helianthus annuus ‘Black Oil’)], and three lettuce (Lactuca sativa) cultivars, Othilie, Xandra, and Rouxai, were foliar sprayed once daily with water containing 0, 25, 50, 75, 100, 125, 150, or 200 mg·L−1 of H2O2 from seed to harvest under greenhouse conditions. Leaf damage was assessed at harvest using two distinct methods: 1) the percentage of damaged leaves per tray and 2) a damage index (DI). Applied H2O2 concentrations, starting from 25 mg·L−1, increased the percentage of damaged leaves in every species except ‘Black Oil’ sunflower, which remained unaffected by any applied concentration. Symptoms of leaf damage manifested in similar patterns on the surface of microgreen cotyledons and lettuce leaves, while mean DI values and extent of damage were unique to each crop. Fresh weight, dry weight, and leaf area of all crops were not significantly affected by daily H2O2 spray. Identifying how foliar H2O2 damage manifests throughout the crop, as well at individual cotyledon or leaf surfaces, is necessary to establish an upper concentration threshold for H2O2 use. On the basis of the aforementioned metrics, maximum recommended concentrations were 150 mg·L−1 (radish), 100 mg·L−1 (arugula) for microgreens and 125 mg·L−1 (‘Othilie’), 75 mg·L−1 (‘Rouxai’), and 125 mg·L−1 (‘Xandra’) lettuce.

Open access

Jaysankar De, Aswathy Sreedharan, You Li, Alan Gutierrez, Jeffrey K. Brecht, Steven A. Sargent and Keith R. Schneider

Cooling procedures used by blueberry (Vaccinium sp.) growers often may include delays up to 24 hours that can damage the fruit through rough handling and adverse temperatures, thereby potentially compromising quality and, subsequently, safety. The objectives of this experiment were to compare forced-air cooling (FAC) compared to hydrocooling without sanitizer (HW) and hydrocooling with sanitizer (HS) regarding the quality and shelf life of southern highbush blueberry [SHB (Vaccinium corymbosum)] and to determine the efficacy of these treatments for reducing Salmonella in SHB. Freshly harvested SHB that were inoculated with a five-serovar cocktail of rifampin-resistant Salmonella were rapidly chilled by FAC or hydrocooling (HW and HS) using a laboratory model system. FAC did not show any significant reduction (P > 0.05) in Salmonella or in the effects on the microbiological quality of blueberries. HW and HS reduced Salmonella by ≈2 and >4 log cfu/g SHB, respectively, on day 0. These postharvest treatments were also evaluated for their ability to help maintain fruit quality throughout a storage period of 21 days at 1 °C. Hydrocooling (both HS and HW) provided more rapid cooling than FAC. Hydrocooled blueberries showed significant weight gain (P < 0.05), whereas FAC resulted in a slight, but insignificant (P > 0.05), reduction in final weight. The results of hydrocooling, both HS and HW, shown in this study could help to extend the shelf life while maintaining or increasing the microbiological quality of fresh market blueberries. Information obtained by this study can be used for developing the best temperature management practices to maintain the postharvest safety and quality of blueberries.

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Ryan C. Costello, Dan M. Sullivan, David R. Bryla, Bernadine C. Strik and James S. Owen

New markets for organic northern highbush blueberry (Vaccinium corymbosum L.) have stimulated interest in using composts specifically tailored to the plant’s edaphic requirements. Because composts are typically neutral to alkaline in pH (pH 7 to 8), and blueberry requires acidic soil (pH 4.2 to 5.5), we investigated elemental sulfur (S0) addition as a methodology for reducing compost pH. The objectives were to 1) characterize initial compost chemistry, including the pH buffering capacity of compost (acidity required to reduce pH to 5.0), 2) measure changes in compost chemistry accompanying acidification, and 3) evaluate plant growth and mineral nutrition of blueberry in soil amended with an untreated or acidified compost. Ten composts prepared from diverse feedstocks were obtained from municipalities and farms. Addition of finely ground S0 reduced compost pH from 7.2 to 5.3, on average, after 70 d at 22 °C, and increased the solubility of nutrients, including K (from 22 to 36 mmol(+)/L), Ca (from 5 to 19 mmol(+)/L), Mg (from 5 to 20 mmol(+)/L), and Na (from 6 to 9 mmol(+)/L). Sulfate-S, a product of S0 oxidation, also increased from 5 to 45 mmol(−)/L. The composts were incorporated into soil at a high rate (30% v/v) in a greenhouse trial to evaluate their suitability for use in blueberry production. Shoot and root growth were strongly affected by compost chemical characteristics, including pH and electrical conductivity (EC). Potassium in compost was highly variable (2–32 g·kg−1). Concentration of K in the leaves increased positively in response to compost K, whereas shoot dry weight and root growth declined. Leaf Mg also declined in response to compost K, suggesting that elevated K concentrations in compost may cause Mg deficiency. Composts with the highest K were also high in total N, pH, and EC. Compost acidification to pH ≤ 6 improved growth and increased leaf Mg concentration. On the basis of these results, composts derived from animal manures or young plant tissues (e.g., green leaves) appear to be unsuitable for high-rate applications to blueberry because they usually require high amounts of S0 for acidification and are often high in EC and K, whereas those derived from woody materials, such as local yard debris, appear promising based on their C:N ratio, compost acidification requirement, and EC.

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Camilo Escalante-Magaña, Luis F. Aguilar-Caamal, Ileana Echevarría-Machado, Fátima Medina-Lara, Lucila Sánchez Cach and Manuel Martínez-Estévez

Water stress is the main factor responsible for decreased productivity, which affects the growth and development of crops. Plants respond to stress by accumulating compatible solutes, which have a key role in osmotic adjustment, thereby resulting in osmoprotection of the plants. The loss of water can increase the concentration of compatible osmolytes and molecules that regulate the plant metabolism. These solutes can be metabolized as sugars (sucrose, fructose, trehalosa), amino acids (proline), an amphoteric quaternary amine (glycine betaine), and other low-molecular-weight metabolites. However, among all these compatible solutes, proline and glycine betaine occur the most. Proline is an amino acid that can accumulate in low concentrations under optimal conditions; however, stress conditions contribute to its increased content. Few data are available regarding the levels of endogenous glycine betaine on Solanaceae, which is considered a nonaccumulator under water deficit conditions. The objective of this research was to evaluate the role of compatible osmolytes, glycine betaine and proline, in Capsicum sp. plants under different water deficit conditions. In this study, the presence of endogenous levels of proline and glycine betaine in two species of pepper (Capsicum chinense var. Genesis and Rex and Capsicum annuum var. Padron) were found. The concentration levels of proline were 362, 292, and 246 μmol·g−1 DW for Genesis, Rex and Padron respectively, and irrigation conditions (rehydration) of proline levels increased to 381, 395, and 383 μmol·g−1 DW at 21 days. However, glycine betaine levels were 30–70 μmol·g−1 DW. The relative water content, electrolyte leakage, and soil water potential were also analyzed; therefore, the information suggests that proline contributes better to tolerance to water deficit in the genus Capsicum after 14 days of water deficit treatment. It seems that the contribution of glycine betaine is less effective than that of proline; therefore, it does not have an important role in osmotic adjustment.

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Harwinder Singh Sidhu, Juan Carlos Díaz-Pérez and Daniel MacLean

Controlled atmosphere (CA) storage has been observed to prolong the shelf life of fresh produce. The objective of this study was to determine whether CA storage performed better than regular air (RA) storage in maintaining fruit quality of six pomegranate (Punica granatum L.) cultivars grown in the state of Georgia. Pomegranate fruit produced in Ty Ty, GA in 2010 and 2011 were stored in CA [5% CO2 + 3% O2, 5 °C, 90% to 95% relative humidity (RH)] or RA (5 °C, 90% to 95% RH) for 3 months. Pomegranate whole fruit and juice were evaluated for various physical and chemical attributes at the end of storage. Fruit differed by cultivar for rind smoothness, fruit cracking, disease incidence, and chilling injury (CI). Fruit stored in CA had a smoother and less shriveled rind, lower CI, fewer disease severity symptoms, and thus better quality than fruit stored in RA. Fruit rind color, total soluble solids (TSS), titratable acidity (TA), and anthocyanin content in fruit juice were unaffected by storage method. The results showed that pomegranate fruit quality was better sustained under CA compared with RA storage.

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Jean Carlos Bettoni, Aike Anneliese Kretzschmar, Remi Bonnart, Ashley Shepherd and Gayle M. Volk

The availability of and easy access to diverse Vitis species are prerequisites for advances in breeding programs. Plant genebanks usually maintain collections of Vitis taxa as field collections that are vulnerable to biotic and abiotic stresses. Cryopreservation has been considered an ideal method of preserving these collections as safety back-ups in a cost-effective manner. We report a droplet vitrification method used to cryopreserve 12 Vitis species (Vitis vinifera cvs. Chardonnay and ‘Riesling, V. actinifolia, V. aestivalis, V. jacquemontii, V. flexuosa, V. palmata, V. riparia, V. rupestris, V. sylvestris, V. ficifolia, V. treleasi, and V. ×novae angeliae) using shoot tips excised from plants grown in vitro. Our results demonstrated wide applicability of this technique, with regrowth levels at least 43% for 13 genotypes representing 12 Vitis species. We demonstrated that the droplet vitrification procedure can be successfully replicated by technical staff, thus suggesting that this method is ready for implementation.