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Oncidesa Gower Ramsey ‘Honey Angel’ is a cut flower crop of high economic value worldwide. The regulation of flowering is important for cut flower production scheduling. However, its flowering transition mechanism is still unclear. Oncidesa usually flowers at the end of the growth cycle for each pseudobulb; this timing is probably related to carbohydrate accumulation. During this study, we investigated the carbohydrates in the pseudobulbs from juvenile plants to adult plants and compared the carbohydrates in flowering and nonflowering adult plants. The current pseudobulb and back pseudobulbs of the plants at 0, 0.5, 1.0, 1.5, and 2.0 years after having been moved out of the tissue culture flask were collected. The first pseudobulb formed at 0.5 years, and plants had fulfilled four growth cycles and flowered at 2.0 years. Each successive current shoot grew larger and the back shoot number progressively increased after each new growth cycle. The concentration of total soluble sugars in the current shoot increased from 5.5% of dry weight at 0.5 years to 20.2% of dry weight at 1.5 years. Conversely, the starch concentration decreased in the current pseudobulb as the plants matured. The starch concentration in the back pseudobulbs did not change when the plant grew a new shoot. The starch concentrations in the back pseudobulbs ranged from 33.2% to 57.5% of dry weight, but the combined content of starch in all of the back pseudobulbs increased significantly from 168 mg at 0.5 years to 4608 mg at 2.0 years because of the increasing number of back shoots. The starch in the first back pseudobulb of the nonflowering adult plants accounted for 18.0% of dry weight, which was lower than that of the flowering plants (48.3%). There was no significant difference in total soluble sugars in the current pseudobulb of the nonflowering and flowering plants. Overall, we revealed that the increase in the back shoot number increased the total amount of reserve carbohydrates as the plant reached reproductive maturity. A low starch level was observed in nonflowering adult plants. In both cases, flowering plants had higher starch storage in the back pseudobulbs, suggesting that carbohydrates might regulate the flowering of Oncidesa Gower Ramsey ‘Honey Angel’.

Open Access

The production of melons (Cucumis melo L.) in greenhouses relies on pollination. Extreme temperature and insufficient light reduce not only flower visitation by pollinators but also pollen viability, resulting in inefficient pollination. In this study, we investigated the effects of forchlorfenuron [(N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU)] on the fruit setting and growth of oriental melons (C. melo L. var. makuwa Makino). The primary objective was to devise a new strategy for the management of oriental melons. Treatment with 5 mg·L−1 CPPU a day before flowering (T1), on the day of flowering (T2), and a day after flowering (T3) increased the fruit setting rate (by 20.1% to 30%) in melons subjected to artificial pollination (AP) or no pollination (NP) compared with the rate in those subjected to only artificial pollination without CPPU (CK). CPPU treatment induced unfertilized seeds; in addition, a tendency toward parthenocarpy was noted. The highest fruit setting rate (∼95%) was noted in plants subjected to the following treatments: AP+T1 and NP+T3. The rates of abnormal fruit formation decreased from 45.2% of CK group to 9.4% in plants subjected to AP+T1 and to 19.4% in those subjected to NP+T3. Elevated exogenous concentrations of CPPU markedly increased fruit weight. Plants subjected to NP+10 mg·L−1 CPPU bore the heaviest fruits (541.0 g), which were heavier than those borne by plants subjected to AP+10 mg·L−1 CPPU. CPPU treatment reduced the fruit cavity ratio in a concentration-dependent manner from 47.3% to 33.6% and increased the pulp thickness from 1.5 to 2.5 cm. Notably, supplementary CPPU treatment exerted no significant effects on fruit traits. Regarding taste, inconsistent results were obtained for sugar accumulation. Although the content of cucurbitacin B increased immediately after the initial CPPU treatment, it markedly decreased after 15 days of CPPU treatment. Therefore, mature melons did not have a bitter taste.

Open Access

In the absence of controlled sufficiency studies, foliar interpretations for many horticultural crops are based on survey concentrations from small data sets. In addition, both survey and sufficiency ranges provide little interpretation regarding zones that are above or below the concentration range deemed “sufficient.” While providing a critical initial set of ranges, it was based on a limited set of data and therefore improvements in interpretation of data are needed. This study presents a novel method based on 1950 data points to create data-driven nutrient interpretation ranges by fitting models to provide more refined ranges of deficient (lowest 2.5%), low (2.5% to 25%), sufficient (25% to 75%), high (75% to 97.5%), and excessive (highest 2.5%). Data were analyzed by fitting Normal, Gamma, and Weibull distributions. Corresponding P values were calculated based on the Shapiro-Wilk test for normality for the Normal and Gamma distributions, and the Kolmogorov-Smirnov test was used for the Weibull distribution. The optimal distribution was selected based on the lowest Bayesian Information Criterion (BIC) value and visual fitness. The Weibull distribution best represented nitrogen, phosphorus, potassium, calcium, manganese, zinc, and copper, and the Gamma distribution best represented magnesium, sulfur, iron, and boron. Using the selected distributions, we propose a refined set of nutrient evaluation ranges for greenhouse-grown lettuce. These refined standards will aid growers and technical specialists in more accurately interpreting leaf tissue sample data.

Open Access

Hydroponic growing systems are advantageous for nutrient studies in which root data are important because they alleviate the laborious and time-consuming task of washing roots to remove soilless substrate particulates from them. However, the growing system should be optimized for the crop of interest. Our overall objective was to develop a protocol for hydroponic strawberry (Fragaria ×ananassa) production that provided growth equal to or better than soilless substrate. Plants were initially grown in perlite, sand, deep water culture (DWC), or a peat-based soilless substrate. Aboveground plant growth in DWC was similar to that of plants grown in the peat-based substrate and required minimal effort to harvest the entire root system. However, the pH of the DWC nutrient solution decreased to 4.0 ± 0.1 (mean ± SE) when plants were provided a modified strawberry (Yamazaki) nutrient solution with a ratio of nitrate (NO3 ) to ammonium (NH4 +) of 80:20. As a result, a subsequent trial was conducted to evaluate the buffering capacity of nutrient solutions with NO3 to NH4 + ratios of 0:100, 20:80, 50:50, 60:40, 80:20, or 100:0, with the addition of potassium bicarbonate (KHCO3). Up to 2.6 mM KHCO3 did not provide adequate buffering in nutrient solutions containing NH4 + (0:100 to 80:20 treatments), and nutrient solution pH decreased by ∼1.5 units every 2 to 3 days. The 100% NO3 nutrient solution, however, maintained a stable pH of 5.9 ± 0.1 when buffered with 0.8 mM KHCO3. Finally, 2(N-Morpholino)ethanesulfonic acid (MES) was evaluated as a potential buffering agent for DWC strawberry production. Plants were grown in a nutrient solution with a 60:40 ratio of NO3 :NH4 +. The buffering capacity of the nutrient solution increased as the MES concentration supplied increased from 1 to 5 mM, and the 5 mM MES treatment maintained a pH of 5.6 ± 0.2. In summary, strawberry plants can successfully be grown hydroponically in DWC, provided that nutrient solution pH is adequately managed. The addition of MES buffer provided better pH stability than KHCO3.

Open Access

Space availability is one of the largest barriers to urban agriculture. One way around this issue that urban farmers in some parts of the world are exploring is moving their farming activities to building rooftops. One method of rooftop farming in use is row agriculture using green roof technology. Vegetable crop plants, which typically require more water and more nutrients than the ornamental species found on green roofs, require irrigation and the use of fertilizers. One nutrient management practice that some rooftop farmers are using is the addition of compost, which could lead to changes over time in the water-holding capacity, organic matter content, and weight of green roof media. This practice and its long-term implications have not been well-studied. Green roof platforms were created to examine how the annual additions of compost in quantities of 0, 0.33, 0.66, and 1 kg/m2 affect runoff water quality and green roof media properties. Runoff water samples were collected and analyzed for pH, conductivity, color, turbidity, and nitrate nitrogen, ammonia nitrogen, total phosphorus, and potassium contents. Compost treatment had no effect on any water quality metric except for color, which had slightly different changes over time in the different compost treatments. The lack of difference among the treatments may be attributed to the low nutrient content of the compost and continued use of fertilizers to provide nutrients. Most samples observed in this study exceeded the US Environmental Protection Agency water quality guidelines for nitrate nitrogen and phosphorus and were similar to values observed in the green roof literature regarding agricultural and ornamental green roofs. This has potential implications for surface water quality and eutrophication, especially as green roof agriculture increases.

Open Access

Ultradwarf bermudagrass (UDB) putting greens grown in subtropical and temperate climates can face elevated risk of winter injury from cold temperatures. Trinexapac-ethyl (TE) inhibits UDB growth potentially reducing spring green-up and overexertion of carbohydrate reserves for UDB during the cold de-acclimation period. A field study was conducted to determine the effect of fall and winter TE applications on the visual quality and color of UDB putting greens in Virginia from the cold acclimation phase through the cold de-acclimation phase. A second controlled-environment study was conducted to determine how TE applications to UDB during cold acclimation affected UDB cold tolerance. In the first study, plots were treated with 0.026 kg⋅ha−1 a.i. every 14 days, 0.013 kg⋅ha−1 a.i. every 14 days, or 0.013 kg⋅ha−1 a.i. every 7 days either in the fall only or in the fall and winter. A nontreated control was included for comparison. For the second study, cup-cutter plugs (10.8-cm diameter) of UDB were treated with 0.026 kg⋅ha−1 a.i. every 14 days from the time growth resumed after green-up through cold acclimation or not treated with TE. Plugs were then exposed to −9.4 °C for 4, 6, 8, or 10 hours and placed into a greenhouse to green up. The GC50 values (exposure time to reduce bermudagrass green cover by 50% 6 days after exposure to −9.4 °C) for the treatments were then calculated based on exposure time and percent green-up. In the first study, TE applications improved UDB quality >3.8%. However, TE applications reduced UDB color, and trends exhibited this reduction in color particularly during the late cold acclimation, winter dormancy, and early cold de-acclimation phases. In the second study, TE applications reduced GC50 values by >10.9% compared with nontreated plugs, suggesting TE reduces UDB cold tolerance during the cold acclimation phase.

Open Access

Pulse irrigation, the practice of applying water in small doses over time, is known to reduce deep percolation and runoff and, relative to irrigating in single continuous applications, can increase plant growth and production by supplying water and nutrients at an optimal rate. The objective of the present study was to determine whether pulse irrigation was beneficial in red raspberry (Rubus idaeus L. ‘Wakefield’). Treatments included continuous or pulse drip irrigation and were evaluated for three growing seasons (2018–20) in a commercial field with silt loam soil. Continuous irrigation was applied up to 4 hours/day, whereas pulse irrigation was programmed to run for 30 minutes every 2 hours, up to eight times/day, using the same amount of water as the continuous treatment. Pulsing improved soil water availability relative to continuous irrigation and, by the second and third year, increased fruit production by 1210 to 1230 kg·ha−1, which, based on recent market prices, was equivalent to $2420 to $2460/ha per year. Much of this yield increase occurred during the latter 3 to 4 weeks of the harvest season and was primarily due to larger fruit size during the second year and more berries per plant during the third year. In 1 or both years, pulse irrigation also produced more canopy cover, larger cane diameters, and higher concentrations of Mg and S in the leaves than continuous irrigation, but it reduced K and B in the soil and had variable effects on sugar-to-acid ratio in the berries. On the basis of these results, pulsing appears to be an effective means of irrigating raspberry plants in sandy or silty loam soils, but more research is needed to determine whether it is useful technique in heavier soil types.

Open Access

Eutypa dieback of grapevine is a trunk disease that impacts vineyard productivity worldwide. Grape germplasm is typically evaluated for resistance to Eutypa dieback through controlled inoculations in the greenhouse, although the high level of replication required of this approach (40 plants per genotype) can limit the total number of genotypes evaluated. An alternative approach is to evaluate naturally infected genotypes in the field. We rated the incidence and severity of vines with the diagnostic leaf symptoms of Eutypa dieback and the incidence of mortality among such vines of 973 Vitis vinifera accessions (planted in duplicate) at the US Department of Agriculture, National Clonal Germplasm Repository in Davis, CA, USA, which is maintained as a living collection for grape research. Across 3 years and spanning a total of 5 years (2011, 2013, and 2015), 120 accessions had leaf symptoms in one or more years (“susceptible accessions”). Courbu blanc [Davis Vitis identification tag (DVIT) 2313], Frankenthal blanc (DVIT 2115), and Pinot gris (DVIT 0907) were the only accessions with leaf symptoms each year. Accessions with the most severe leaf symptoms (a rating of 5 points) were Chasselas Napoleon (DVIT 0375) and Queen of the Vineyard (DVIT 0496). We identified susceptible accessions—namely, those related to ‘Chasselas’ and ‘Muscat’—with a shared genetic background, based on a previous single nucleotide polymorphism genotyping effort of the collection. Especially for grapevine, a long-lived perennial that is meant to produce a crop for decades, knowledge of susceptible accessions and their pedigrees can help inform breeding programs and studies on the host response to infection.

Open Access

The formation of onion (Allium cepa) bulbs is affected by photoperiod length and onion germplasm is commonly classified as short- (SD), intermediate-, or long-day (LD) types. The objectives of this study were to develop a segregating family from a cross between doubled haploids (DHs) of LD and SD onions and complete genetic analyses of bulb shape and volume, as well as daylength effects on bulbing. DH parents and F1 and F2 progenies were grown in a greenhouse under lengthening days. The diameters of the neck constriction and pseudostems were measured weekly and their ratio was used as the determinant of bulbing. Bulbs were harvested when the foliage collapsed and the diameters and heights of individual bulbs were measured and used to calculate a shape index (diameter divided by height) and bulb volume. Single nucleotide polymorphisms (SNPs) were genotyped and a genetic map of 112 SNPs constructed. Genetic analysis revealed two highly significant quantitative trait loci (QTL) affected bulbing under increasing daylengths, and both QTL showed significant additive effects with no dominance. One highly significant QTL was detected for bulb-shape index and explained 30% of phenotypic variation for bulb shape. Three additional QTL were slightly above the significance threshold, and together these four QTL explained over 50% of the phenotypic variation for bulb shape. No significant QTL were detected for bulb volume. These results reveal that bulb-shape and daylength effects on bulbing are relatively simply inherited, and this research should facilitate introgression of traits between onion populations of different daylength sensitivities and efforts to modify bulb shape.

Open Access