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Flow cytometry has been widely used to estimate relative and absolute genome sizes (DNA contents) of plants for more than 50 years. However, the accuracy of these estimates can vary widely because of many factors, including errors in the genome size estimates of reference standards and various experimental methods. The objectives of this study were to reassess genome sizes of commonly used reference standards and quantify sources of variation and error in estimating plant genome sizes that arise from buffers, confounding plant tissues, tissue types, and plant reference standards using both 4′,6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI) fluorochromes. Five separate studies were performed to elucidate these objectives. Revised estimates of genome sizes of commonly used plant reference standards were determined using human male leukocytes as a primary standard with an updated genome size (6.15 pg; 12.14% lower than that of earlier studies) using both DAPI and PI fluorochromes. Comparison of six different buffers (Galbraith’s, LB01, MB01, MgSO4, Otto’s, and Sysmex) resulted in variations in genome size estimates by as much as 18.1% for a given taxon, depending on the buffer–fluorochrome combination. The addition of different confounding plant tissues (representing 10 diverse taxa and associated secondary metabolites) resulted in variations in genome size estimates by as much as 10.3%, depending on the tissue–fluorochrome combination. Different plant tissue types (leaf color/exposure and roots) resulted in a variation in genome size estimates of 10.7%, independent of the fluorochrome. The selection of different internal reference standards introduced an additional variation in genome size estimates of 5.9%, depending on the standard–fluorochrome combination. The choice of fluorochrome (DAPI vs. PI) had one of the largest impacts on genome size estimates and differed by as much as 32.9% for Glycine max ‘Polanka’ when using human male leukocytes as an internal standard. A portion of this variation (∼10.0%) can be attributed to the base pair (bp) bias of DAPI and variations in Guanine-Cytosine (GC):Adenine-Thymine (AT) ratios between the sample and standard. However, as much as 22.9% of the variation in genome size estimates may result from how effectively these fluorochromes stain and report the genome. The combined variation/error from all these factors (excluding variation from bp bias for different fluorochromes, and assuming variations from confounding tissues and tissue types to both result from secondary metabolites) totaled 57.6%. Additional details of how selected factors impact accuracy, precision, and the interaction of these factors are presented. Overall, flow cytometry can be precise, repeatable, and extremely valuable for determining the relative genome size and ploidy of closely related plants when using consistent methods, regardless of fluorochrome. However, accurate determination of the absolute genome size by flow cytometry remains elusive, and estimates of genome size using flow cytometry should be considered gross approximations that may vary by ±29% or more as a function of experimental methods and plant environments. Additional recommendations of best practices are provided.

Open Access

Cancer bush (Lessertia frutescens L.) is an important medicinal plant that is rich in health beneficial compounds. It is commonly used in traditional medicine and as an ornamental plant. Heat stress is the most threatening abiotic factor restricting plant growth, thus causing crop yield and economic losses worldwide. The application of plant-derived biostimulant is as an innovative and promising approach for improving plant growth and productivity. The study was aimed to investigate the effect of moringa (Moringa oleifera Lam.) seed extract (MSE; 5%) either alone or in combination with salicylic acid (SA; 40 mg/L) on the growth, bioactive, and phytohormone attributes of cancer plants subjected to heat stress (38 °C for 2 hours for 5 days). Plants that were not treated were used as control. Plant pots were arranged in a randomized complete block design (RCBD) for treatments (MSE, SA, and MSE + SA) at 7-day intervals during the experiment. Both MSE and MSE + SA foliar application effectively increased plant growth characteristics and total carotenoids contents, and reduced electrolyte leakage and had no symptoms of wilting compared with SA and control. Plants treated with MSE showed higher number of branches and concentrations of abscisic acid (ABA), jasmonic acid (JA), and indole-3-acetic acid (IAA), and lower superoxide and hydrogen peroxide compared with other treatments and control. Also, plants treated with MSE + SA showed higher total chlorophylls and glutathione concentrations compared with other treatments and control. Overall, the application of MSE either alone or in combination with SA enhanced plant growth and productivity of heat-stressed cancer bush plants.

Open Access

Traditional methods of garlic fertilization involve large amounts of balanced fertilizer with equal proportions of N, P, and K, leading to nutrient imbalances, reduced yield and nutritional quality, and elevated risk of environmental pollution. This study for the first time measured garlic nutrient absorption and mineral elements status in garlic fields. In addition, a garlic-specific fertilizer formula and recommended rate were designed and applied in multiple garlic fields during the 2019–21 growing season. We assessed the performance of garlic-specific fertilizer in terms of yield, quality, and nutrient utilization efficiency. We showed that garlic prefers to absorb N and K, and its absorption of P was much lower. Deficiencies in Cl, Mn, S, and Fe are found in 98.7%, 56.1%, 22.8%, and 11.9% of garlic fields. Compared with farmer fertilization, the garlic-specific fertilizers increased sprout yield by 12.9% to 30.5%, bulb yield by 11.0% to 33.5%, and net income by 18.2% to 45.6%. Furthermore, it improved the nutritional quality [vitamin C (Vc), soluble sugar (SS), and soluble protein] of the garlic and reduced the accumulation of nitrate. The formula of special fertilizer was more in line with the law of garlic nutrient absorption, increasing the nutrient utilization effect, reducing the environmental risks. Application of specific fertilizer increased N, P, and K partial productivity by 26.6% to 50.1%, 82.6% to 116.5%, and 54.6% to 83.3%, respectively. These results suggest that replacing balanced fertilizers in the garlic market with garlic-specific fertilizers can improve garlic farmers' incomes and soil health.

Open Access

In 2020, the COVID-19 pandemic changed the way many businesses conducted business. Notably, regulations imposed by states impacted how green-industry firms sold their plants and landscape products. However, not all states implemented the same stringency of regulations. Using an online consumer survey implemented in Jan 2021, we examine the impact of varying regulation stringencies across five treatment groups (Michigan, and New York, and low, medium, and high stringency). We estimate the difference between 2020 and 2019 self-reported expenditures, in conjunction with propensity score matching to compare each treatment with the other treatments. Results indicate that, for the most part, states with greater stringency associated with their COVID regulations did not impact plant and landscape expenditures negatively between 2019 and 2020. However, Michigan consumers did spend significantly less than medium- and high-stringency states for landscape products. Michigan was one of only two states that put qualifications on green-industry firms, and it was the only state to list green-industry firms as nonessential. Also, New York consumers spent more than low-stringency states, and low-stringency states spent less than high-stringency states for plants. Furthermore, there were no differences in online expenditures between state treatment groups. From a policy perspective, regulation type (i.e., shutting down green-industry sectors as Michigan did) had varying impacts across product categories within the green industry.

Open Access

Phalaenopsis is a globally popular potted plant possessing a few aromatic cultivars, but analysis of volatile organic compounds (VOCs) in these cultivars is limited. Here, using nonaromatic cultivar Phal. Big Chili as a control, flower VOCs of four aromatic cultivars were investigated by headspace solid-phase microextraction in conjunction with gas chromatography–mass spectrometry (GC-MS). The results revealed that 43 VOCs classified into seven categories were identified in the nonaromatic Phal. Big Chili and four aromatic cultivars. Hexyl acetate and hexan-1-ol were common VOCs in aromatic cultivars. On the basis of partial least squares discriminant analysis, the five cultivars were classified into three groups, the nonaromatic Phal. Big Chili (group 1) and the strong-aromatic Phal. Cherry Tomato (group 2) were easily distinguished from the other three aromatic cultivars (group 3). Moreover, 17 key VOCs with the different aromatic thresholds and characteristics were identified in the four aromatic cultivars, and the types and relative contents of key VOCs varied among the aromatic cultivars, resulting in different characteristics and intensities of floral fragrance in aromatic cultivars. In aromatic cultivars, the types and relative contents of key VOCs in Phal. Cherry Tomato significantly exceeded those in the other three cultivars. Eight key VOCs belonging to terpenoids, olefins, and alcohols had the highest relative contents in Phal. ‘Cherry Tomato’, which led to a strong and mixed aromatic type containing cedarwood, camphor, and mint fragrances.

Open Access

To effectively manage crop production in a greenhouse, it is essential to understand the natural light environment and physiological responses of the plants to light. This study investigated the dynamics of photosynthetic photon flux densities (PPFD) and light quality within the canopies of greenhouse-grown eggplant (Solanum melongena) and the photosynthetic capacities of leaves at different locations within the canopies. The light environment was quantified at 0.2-m intervals within (intra-canopy) and adjacent to (extra-canopy) the crop canopy on both sunny and cloudy days within a commercial greenhouse located in Leamington, Ontario, Canada. Our results indicated a linear decline in extra-canopy PPFD on both sunny and cloudy days, but an exponential decrease in intra-canopy PPFD. The intra-canopy PPFD decreased by 91% and 76% between 0 m and 0.4 m from the canopy apex on sunny and cloudy days, respectively. The lower canopy (0.6–1.2 m) light spectrum consisted largely of far-red light, equal amounts of red light and green light, with a lower percentage of blue light. Parameters derived from leaf-level light response curves indicated that the light-saturated net carbon exchange rate, light saturation point, and light compensation point decreased as the distance from canopy apex increased, whereas quantum yield was unaffected. Thus, leaves in the lower canopy were less efficient at using high PPFD, but they displayed no deterioration of photosynthetic machinery. Based solely on photosynthetic capabilities, leaves between 0 and 1.0 m from the canopy apex should not be removed to decrease the total plant sink strength.

Open Access

Penstemon, with more than 250 species native to North America, holds significant aesthetic and ecological value in Utah, supporting diverse pollinators. Despite their significance, the survival of penstemon is threatened by challenges such as habitat loss, climate change, and Utah’s naturally high soil salinity. To address these challenges and understand their adaptability, this study evaluated the salt tolerance of two penstemon species [Penstemon davidsonii (Davidson’s penstemon) and Penstemon heterophyllus (foothill penstemon)] under controlled greenhouse conditions. The aim was to develop baseline information for nursery production and landscape use that utilize reclaimed water for irrigation. Plants were irrigated weekly with a nutrient solution at an electrical conductivity (EC) of 1.0 dS·m−1 as control or a saline solution at an EC of 2.5, 5.0, 7.5, or 10.0 dS·m−1 for 8 weeks. Half of the plants were harvested after four irrigation events, and the remaining plants were harvested after eight irrigation events. At harvest, visual rating (0 = dead and 5 = excellent without foliage salt damage), plant width, number of shoots, leaf area, shoot dry weight, leaf greenness [Soil Plant Analysis Development (SPAD)], stomatal conductance, and canopy temperature were collected to assess the impact of salinity stress. In both species, salt damage was dependent on the salinity levels and length of exposure. After four irrigation events, both species exhibited foliage damage that increased in severity with rising EC. The most severe damage was observed in plants receiving saline solution at an EC of 10.0 dS·m−1. After eight irrigation events, P. davidsonii exposed to a saline solution with an EC of 10.0 dS·m−1 received a visual rating of 0, whereas P. heterophyllus had a visual rating of 0.4. Both species exhibited salinity-induced effects, with variations observed in the specific parameters and the degree of response. Penstemon davidsonii exhibited significant salinity stress, as indicated by reduced leaf area, shoot dry weight, SPAD reading, and stomatal conductance with increasing EC of the saline solution. In addition, in both species, at both harvests, canopy temperatures increased either linearly or quadratically by 8% to 36% as the EC levels of the saline solution increased. These results indicate that P. davidsonii was more sensitive to salinity stress than P. heterophyllus.

Open Access

The onion processing industry produces hundreds of thousands of tons of onion waste annually. Normally, onion peel waste is dumped in landfills, which creates additional sources of greenhouse gases. Research has validated that onion peel is a concentrated source of bioactive compounds; therefore, it can be turned into useful agricultural products such as soil amendments and possibly biostimulants. This study conducted three experiments to investigate the plant growth-promoting potential of an onion juice concentrate (OJC). The first experiment explored whether the application of OJC could increase plant growth of Bermuda grass, lettuce, and bok choy. The second experiment evaluated the effects of foliar and subsurface drench applications of OJC on bok choy and lettuce growth. The third experiment investigated the interaction between OJC application methods and fertilizer type on bok choy and radish growth. The results indicated that foliar applications of OJC of 1% to 2% concentrations increased the yield of bok choy and its overall growth. Subirrigation with OJC, however, enhanced the root growth of bok choy, lettuce, and radish. Notably, the combined approach of foliar and subirrigation applications further promoted the growth of both bok choy and radish. Comparing across experiments, longer OJC application periods emerged as a promising strategy for amplifying its growth-promoting benefits. Overall, our findings suggest that OJC holds promise for promoting sustainable agriculture. This potential comes from its ability to enhance both the growth and yield of vegetable crops like bok choy, lettuce, and radish while simultaneously reducing waste.

Open Access

Mal secco, caused by the fungus Plenodomus tracheiphilus, is a xylem disease that is a limiting factor for lemon production in the Mediterranean. Resistance or field tolerance are major goals for lemon breeders; however, there is scant information regarding the heritability of mal secco resistance in breeding populations. As with other vascular diseases, phenotyping is the bottleneck for ascertaining resistance and susceptibility, and a validated protocol for greenhouse phenotyping would be valuable to accelerate the selection of tolerant trees before field evaluation. We report phenotyping of 148 hybrids of Khasi papeda (Citrus latipes; tolerant to mal secco) × lemon (susceptible to the disease) in field and greenhouse conditions. Field evaluation was performed on all hybrids for 2 to 3 consecutive years on trees subjected to high natural-pathogen pressure. Detection of the fungal infection was performed by visual observation and real-time polymerase chain reaction (PCR). The first infections occurred ≈6 months after planting, but 2 years of observations were needed for a reliable estimation of susceptibility. The spread of the disease did not occur uniformly throughout the plot, with patterns of spread within rows, probably resulting from infections from plant to plant. The possible errors in the estimation of susceptibility as a result of the uneven distribution of infections in the plot were reduced by using more than one replicate tree per hybrid. The correlation between phenotyping scores and cycle threshold values was weak (r = –0.48, P < 0.001). Three years after planting, hybrids clustered into three groups—susceptible, tolerant, and intermediate—based on symptom progression. A subset of 65 self-rooted hybrids was also subjected to stem inoculation in an unheated greenhouse, with two to seven biological replicates per hybrid. Three months after inoculation, the samples were monitored for symptoms appearance and subjected to real-time PCR pathogen quantification. We observed a weak (r = 0.41) but significant (P < 0.001) correlation between phenotypes in the field and the greenhouse, indicating that, in our conditions, field evaluation remains the best method for phenotyping. However, artificial inoculations might help to discard the highly susceptible hybrids before field evaluation.

Open Access