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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

This study estimates the influence of the coronavirus disease 2019 (COVID-19) pandemic on consumer preferences for turfgrass attributes by analyzing data from two surveys conducted in Jan 2019 and Apr 2021. First, the study estimated a mixed logit model to account for individual heterogeneity in preferences. Subsequently, estimates of the willingness to pay (WTP) were compared between periods before and after the pandemic. To show the impact of consumers’ risk attitudes with respect to climate change on their preference for turfgrass attributes, we re-estimated the model according to the risk attitude groups (i.e., risk-seeking vs. risk-averse). Finally, to examine how consumers’ demographic characteristics and risk attitudes are related to their WTP for improved turfgrass attributes, we estimated a random-effect panel data model for each attribute. Our results showed that, overall, consumers’ WTP increased during the COVID-19 pandemic. We also found that the WTP of risk-averse consumers were mostly higher than those of risk-seeking consumers during both time periods. Furthermore, the increase in the WTP observed among the risk-averse group was greater than the increase of the WTP of the risk-seeking group. Our findings imply that the demand for drought-tolerant and stress-resistant turfgrasses would increase with possible future climate changes and infectious disease outbreaks.

Open Access

Rain cracking (hereinafter referred to as macrocracking) severely impacts the production of sweet cherry (Prunus avium). Calcium (Ca) sprays can reduce macrocracking, but the reported responses to Ca sprays are variable and inconsistent. The objective of this study was to establish the physiological mechanism through which Ca reduces macrocracking in sweet cherry fruit. Six spray applications of 50 mM CaCl2 had no effect on macrocracking (assessed using a standardized immersion assay) despite a 28% increase in the Ca-to-dry mass ratio. Similarly, during another experiment, there was no effect of up to nine Ca sprays on macrocracking, although the Ca-to-dry mass ratio increased as the number of applications increased. In contrast, CaCl2 spray applications during simulated rain (in a fog chamber) significantly reduced the proportion of macrocracked fruit. Additionally, immersion of fruit in CaCl2 decreased macrocracking in a concentration-dependent manner. Monitoring macrocrack extension using image analysis revealed that the rate of macrocrack extension decreased markedly as the CaCl2 concentration increased. This effect was significant at concentrations as low as 1 mM CaCl2. Decreased anthocyanin leakage, decreased epidermal cell wall swelling, and increased fruit skin stiffness and fracture force contributed to the decrease in macrocracking. There was no effect of CaCl2 on the cuticle deposition rate. Our results demonstrated that Ca decreased macrocracking when applied to a wet fruit surface either by spraying on wet fruit or by incubation in solutions containing CaCl2. Under these circumstances, Ca had direct access to the cell wall of an extending macrocrack. The mode of action of Ca in reducing macrocracking is primarily decreasing the rate of crack extension at the tip of a macrocrack.

Open Access

Rockwool and peatmoss are commonly used substrates in the greenhouse industry due to their quality, stable pH, exceptional water retention properties and air porosity that is important for plant root development. Although rockwool is commonly used in deep water culture (DWC) hydroponic systems as the base support, there is a lack of studies comparing different types of substrates that could be used in DWC systems, especially considering the increasing market value and awareness of sustainable production in controlled environment agriculture. We identified 13 commercial substrate mixes with different compositions and conducted a series of studies in a DWC system in a greenhouse for three seasons to evaluate their effects on arugula ‘Slow Bolt’ (Eruca sativa L.) and lettuce ‘Summer Crisp’ (Lactuca sativa L.) growth, yield, and quality. The substrates tested significantly influenced the growth, yield, and quality of both arugula and lettuce. The average leaf fresh weight per plant could range from 44 to 190 g for arugula and 89 to 265 g for lettuce. The peat-based products outperformed the coir and other inorganic substrates (phenolic foam, rockwool). The substrate with 75% peat + 25% fine coir produced the greatest plant height, width, and biomass for arugula and lettuce over three growing seasons. Examining arugula and lettuce growth, the fall season produced plants with higher water and nutrient use efficiency, while plants grown during the winter had lower resource use efficiency. Further research is needed to engineer hydroponic substrates suitable for various seasons of leafy green production that results in comparable yield and quality.

Open Access

This study compared supplemental white light-emitting diode (LED) light provided on top of the canopy (top-light) or partially on top and partially as intracanopy light (ICL) in high-wire cucumber (Cucumis sativus) and tomato (Solanum lycopersicum) crops. The aim was to determine the effects of partially substituting top-light by ICL on fruit yield and its underlying yield components. For each crop, three replicate Venlo glasshouse compartments were used. Two cucumber (HiPower and Skyson) and two tomato cultivars (Brioso and Merlice) were planted in the second half of Oct 2020 and grown on stone wool for a period of 15 weeks (cucumber) or 20 weeks (tomato). Light was supplied at either a light intensity of 250 or 375 µmol⋅m−2⋅s−1, provided either as 100% top-light or as 67% (2/3) top-light and 33% (1/3) ICL. For cucumber at the higher light intensity, 50% more fruits were retained and for tomato at the higher light intensity, planting density was 50% higher to keep the plants balanced in terms of source-to-sink ratio. Substituting 33% of top-light with ICL resulted on average in an increase of 17% in fresh fruit yield for both cucumber and tomato. This increase was twice as high at the higher light intensity (20% to 24%) compared with the lower light intensity (10% to 12%). For both cucumber and tomato, the higher yield for ICL treatments resulted mainly from higher total plant dry weight, whereas partitioning to the fruits was hardly affected. For both crops, the higher plant dry weight resulted from a higher light use efficiency. Increasing light intensity from 250 to 375 µmol⋅m−2⋅s−1 resulted in 38% higher total daily light integral (including solar radiation) and 36% to 37% higher total plant dry weight in cucumber. In tomato, the higher light intensity resulted in 33% higher daily light integral and 36% to 40% total plant dry weight. These values are in agreement with the rule of thumb that 1% increment in light results in 1% increase in plant growth. For cucumber, partially substituting top-light by ICL as well as increasing light intensity resulted in longer and greener fruits, whereas tomato fruit quality (Brix, pH) was unaffected by ICL or light intensity. In conclusion, partially substituting top-light by intracanopy light increased fruit yield and this was even more so at higher than at lower supplemental light intensities.

Open Access

There is an increasing interest in producing organic tomatoes (Solanum lycopersicum) in high tunnels (HTs) in the southeast United States. HTs are unheated, passively cooled structures that allow tomato growers to harvest high-quality fruit out of season. However, excessive temperatures inside HTs may negatively impact tomato plant growth and fruit yield. Shade nets have been reported to reduce temperatures inside the HTs. Plastic mulch color has also significantly influenced plant growth and yield under high-temperature conditions. This study aimed to determine the effects of shade net color and plastic mulch color on plant growth, fruit yield, and incidence of tomato yellow leaf curl disease (TYLC) in ‘Red Snapper’ tomato grown in HTs under elevated temperatures (summer-fall) in southern Georgia, USA. Organic ‘Red Snapper’ tomato seedlings were transplanted in HTs in 2019 (Season 1) and 2020 (Season 2). The design was a split-plot randomized block where the main plots were externally mounted shade nets (black, silver, and unshaded; 30% shade factor), and the subplots were plastic mulches (black and white). Compared with black mulch, white mulch improved plant height and stem diameter but did not influence fruit yields. Shade nets reduced HT air temperature and root zone temperature (RZT) but did not affect plant height and stem diameter. The diminished photosynthetic photon flux density (PPFD) under the shade nets reduced marketable fruit yield. Thus, shade nets are not recommended once heat challenges do not limit HT tomato production in Georgia (after about mid-October). Shade nets and plastic mulch inconsistently affected TYLC incidence, severity, and area under the disease progress curve (AUDPC). Additional fruit yield reductions occurred due to TYLC because the incidence was 100% 6 weeks after transplanting. Preliminary insect data showed that shade net treatments had similar sweetpotato whitefly (Bemisia tabaci) numbers. The high TYLC incidence indicates that ‘Red Snapper’ may not be suitable for fall HT tomato production in the southeast United States. More research on shading and heat stress management in HT organic tomato production is necessary.

Open Access