Copper (Cu) is typically adequate at 0.5 μM (0.03 ppm) in hydroponics and at 2 μM (0.125 ppm) in soilless media, but elevated levels can be used to inhibit pathogenic fungal growth. We studied the effect of elevated Cu on the growth of lettuce and tomato in peat-based media and deep-flow hydroponics. Lettuce growth in hydroponics was not hindered until a concentration greater than 4 μM (0.25 ppm) Cu was used, which is eight times greater than the adequate level. Tomato was more tolerant of elevated Cu, with no growth suppression up to 8 μM (0.5 ppm) in hydroponics. Organic matter tightly binds Cu, and bioavailability is thus determined by organic components in soilless media. We confirmed an adsorption capacity of 19 mg Cu per g of peat, which explains why there was no inhibition of lettuce or tomato growth up to 1000 μM (64 ppm) Cu in peat-based media. When chelated with ethylenediaminetetraacetic acid, Cu binding to organic matter was reduced and growth was decreased in lettuce but not tomato. Both species tolerated a 100-fold greater concentration of Cu in peat-based media than in deep-flow hydroponics. Elevated Cu in solution increased concentrations 20 times greater in root tissue than in leaves. These solution and tissue concentrations are greater than identified toxicity thresholds of pathogenic fungal and fungal-like organisms, and could thus be used to suppress root-borne fungal and fungal-like diseases.
Creeping bentgrass (Agrostis stolonifera L.) is a turfgrass species that is widely used on golf courses throughout the United States. In field settings, plants are often subjected to more than one stress at a time, and studying stresses independently is likely insufficient. Stresses, such as heat stress and salt stress, can affect plant hormone levels and, in turn, plant hormone levels can affect how well the plant tolerates stress. The objectives of the experiments were to determine if the levels of heat stress and salt stress used would be detrimental to creeping bentgrass health, and if applying plant growth regulators could improve plant health during stress. During the first experiment, creeping bentgrass was transplanted to hydroponics systems in two different growth chambers. One chamber was set to have day and night temperatures of 35 °C and 30 °C (heat stress), respectively, and the other had day and night temperatures of 25 °C and 20 °C, respectively. Within each chamber, one block received a 50 mM NaCl treatment (salt stress) and the other did not (control). The stress treatments were applied for 14 days. Results of the first experiment indicated that the treatments were sufficient to negatively affect creeping bentgrass growth and health as indicated by fresh shoot and root weights, tillering, electrolyte leakage, and total chlorophyll content (TCC). There were significant interactions of temperature × salt level detected for shoot and root weights and electrolyte leakage. Plants that were exposed to both heat stress and salt stress were more negatively affected than plants exposed to either heat stress or salt stress alone for all metrics except for tillering. The presence of salt reduced tillering regardless of the temperature regimen. During the second experiment, plants were treated the same, but the plant growth regulator (PGR) treatments were also applied. The PGR treatments consisted of two different gibberellic acid (GA) synthesis inhibitor products, 2,4-dichlorophenoxyacetic acid, two different rates of aminoethoxyvinylglycine (AVG), an ethylene synthesis suppressor, and plants that were not treated with the PGR. In addition to the measurements of plant health and growth, dry shoot and root weights were measured. For the TCC, there was a two-way interaction between temperature × PGR treatment. For electrolyte leakage, there was a three-way interaction between temperature × salt level × PGR treatment. Combined heat stress and salt stress negatively affected all plants regardless of PGR treatment, but there were differences between PGR treatments. Plants treated with AVG exhibited improved health and growth compared with the other PGR treatments. These plants had the highest shoot and root masses. Plants treated with GA synthesis inhibitors had the lowest shoot and root masses as well as the lowest TCC when subjected to stress.
Paeonia lactiflora is a high-value crop with a temperature-dependent growth response that requires worldwide production to satisfy year-round demand. The objective of this study was to evaluate production and timing of ‘Coral Charm’ peony as a cool-season crop in the US Intermountain West. High-tunnel and field production were trialed in North Logan, UT, USA (lat. 41.77°N, long. 111.81°W; elevation, 1382 m) with the addition of low tunnels and soil heating methods to advance growth in 2019–21. Soil and air temperatures, as well as the date and quality of harvested stems, were measured. High tunnels yielded 15.7 ± 3.3 to 19.4 ± 2.1 stems/m2 [± standard error (SE)] and the high tunnel alone advanced initial harvest 21 to 34 days earlier than natural field conditions. The field yielded 16.1 ± 1.9 to 20.8 ± 1.6 stems/m2 and staggered production, resulting in a harvest duration up to 38 days across the high tunnel and field. The use of a low tunnel with soil heating advanced the initial harvest date compared with natural (i.e., unmanipulated) high-tunnel and field conditions by 3 and 7 days in 2019, 6 days in 2020, and 16 and 6 days in 2021 in the high tunnel and field, respectively. However, the quality decreased significantly under low tunnels with soil heating within high tunnels, compared with unheated plants, as a result of superoptimal temperatures and humidity that damaged buds and led to an increase in disease and insect pressure. Overall, increasing soil temperature advanced early stages of production when the meristem was below or near the soil surface, whereas increased air temperatures accelerated stem elongation and advanced time to flowering.
A trio of peach cultivars, Crimson Joy, Liberty Joy, and Rich Joy, have been recently released by the US Department of Agriculture breeding program at Byron, GA. They ripen at Byron in early to mid-June, late June to early July, and mid-July, respectively. Additional data on their fruit development are needed to understand the ripening process and optimize harvest timing. This study was designed to measure and compare characteristics of ripening fruit harvested weekly from the three Joy cultivars in two trial orchards. Fruit characteristics were significantly different among the three cultivars, the trial locations, and the harvest weeks. Difference in the five size-related characteristics (fruit weight, flesh weight, pit weight, and equatorial and polar diameters) and soluble solid content (SSC) were statistically significant among the three cultivars. ‘Crimson Joy’ had the smallest averages in the size-related characteristics and ‘Rich Joy’ fruit had the largest. ‘Liberty Joy’ had the firmest fruit and least juice volume and blush rating value at maturation. Trees in the commercial block produced larger fruit than those in the Byron research block. Differences among the harvests were statistically significant for all the fruit characteristics, suggesting that the peach fruit experienced dramatic changes as ripening progressed. The weights and diameters, juice volumes, and SSC continued to increase in the harvests although with reduced firmness. Correlation coefficients varied greatly between these fruit characteristics along with R 2 and P values. The highest positive correlations were observed among fruit weight, equatorial diameter, polar diameter, and flesh weight. Pit weight was positively correlated with them to a lesser extent. Firmness showed substantial negative correlations with several characteristics, including three weights, two diameters, juice volume, SSC, and blush rating value. SSC and titratable acidity were also negatively correlated. The data confirmed that peach fruit continued to size while ripening and should be useful to determine appropriate harvest timing, which could differ for commercial packing vs. roadside sales.
Ginger (Zingiber officinale, Roscoe) is a tropical rhizome crop typically grown from rhizome pieces, but can also be produced from seedlings. No information is available on how the seedling method compares with the rhizome piece method in organic ginger culture. In addition, information on the growing of organic ginger in the mid-Atlantic region is lacking. Some of the challenges include limited knowledge of rhizome storage, types of propagation materials for planting in the field or high tunnel, and acceptable organic fertilizers that will not increase the excess P currently polluting the Chesapeake Bay watershed. The objective of this study was to assess plant development, soil nutrients, and economic feasibility of organic ginger derived from different storage conditions and planting materials when grown in different nutrient sources in a high tunnel. Three types of plant material (single-shoot transplant seedlings derived from 36.5–40.0 g/rhizome, multishoot transplant seedlings derived from 60–120 g/rhizome, and rhizome seeds of 60–120 g) and three fertilizers types [cotton seed meal, 6N–0.9P–0.8K (0.18 kg⋅m–2), plus AZOMITE (1 kg⋅m–2); Nature Safe, 13N–0P–0K (0.07 kg⋅m–2); and Phytamin All Purpose Liquid fertilizer, 4N–1.3P–3.3K (0.26 L⋅m–2)] were used in 2018. In 2019 and 2020, three types of plant material and two fertilizer types at modified rates from the 2018 study, plus two storage containers (pans and flats), were tested. In general, the rhizome storage container did not affect plant height, leaf soil plant analysis development (SPAD) index, and rhizome yield, and its effect on tillers was none or mixed. Fertilizer type had mixed effects on plant height and tiller number, and no effect on the leaf SPAD index. Rhizome yields in 2019 and 2020 were unaffected by fertilizer, but Nature Safe produced a greater benefit-to-cost ratio (BCR) and profitability index (PI) than Phytamin. Soil P was generally less in Nature Safe–fertilized soil than in Phytamin-fertilized soil. Multishoot seedlings produced the greatest rhizome yield, BCR, PI, and tallest plants, and had some of the highest tiller numbers. These findings show that it would be more profitable to use multishoot seedlings as planting material in high tunnels compared with single-shoot seedlings and rhizome seeds. Furthermore, the lower P levels in the Nature Safe–fertilized soils compared with the Phytamin soils, and greater PI suggest that using Nature Safe will be a better choice than Phytamin for growing organic ginger.
Lettuce (Lactuca sativa L.) is the most common leafy vegetable produced hydroponically in the United States. Although hydroponic systems are advantageous due to lower pest and disease pressure, and reduced water and nutrient requirements, the increasing prices of fertilizers, including phosphorus (P), still influences the profitability of hydroponic production of lettuce. Characterizing lettuce germplasm capable of producing high yield using less P inputs may help reduce fertilizer use, production costs, and P loads in wastewater. In this study, 12 lettuce accessions were grown in four experiments in a nutrient film technique system. In the first two experiments, the treatments consisted of two P concentrations (3.1 and 31 mg·L−1). Lettuce cultivated with 3.1 mg·L−1 of P had variable shoot and root biomass, root–shoot ratio, P uptake efficiency, and P utilization efficiency, indicating the existence of genetic variation. Five accessions (‘Little Gem’, 60183, ‘Valmaine’, BG19-0539, and ‘Green Lightning’) were considered efficient to P because produced similar shoot biomass with the low and high P treatments. In the third and fourth experiments, the treatments consisted of two P sources (monosodium phosphate (NaH2PO4) and tricalcium phosphate [TCP; Ca3(PO4)2]. Initially, extra 5 mM of calcium (Ca) was added to the TCP solution to reduce the TCP solubility and, hence, P bioavailability to plants. All accessions produced similar shoot and root weight with both treatments, indicating that the TCP treatment did not cause low-P stress to the plants. After, the extra Ca concentration added to TCP was increased to 10 mM, resulting in low-P stress and a significant reduction in shoot weight of all accessions. Despite the severe P stress, ‘Little Gem’ and 60183 were among the accessions with the least shoot weight reduction in the TCP treatment. Variability was observed in root biomass root–shoot ratio among accessions under the TCP treatment, suggesting that lettuce accessions responded differently to P stress conditions. The genetic variation for P use efficiency (PUE) and PUE-related traits in lettuce grown hydroponically suggests the feasibility of breeding new lettuce cultivars from elite lettuce germplasm adapted to low P availability in hydroponics.