Soilless tomato grown under nutritional stress increases green biomass but not yield or quality in presence of biochar as growing medium

Abstract

Biochar has been reported to improve soil fertility and growing medium performance. However, the role that biochar plays in plant nutrition is not completely understood, especially in plants grown under nutritional stress. Recent research indicates that the addition of biochar increases produce yield of tomato grown under salinity stress and drought; however, little information is available about the effects of biochar on fruit quality parameters. The use of biochar as a growth substrate in an intensive greenhouse cropping system may have the capacity of replacing non-renewable and less sustainable growing media like peat and in addition being a strategy to optimize chemical fertilisation. This work aimed to investigate the effects of biochar, as a potential candidate to replace peat, on tomato growing in soilless conditions under nutritional stress. Plant biomass accumulation, leaf fluorescence and chlorophyll, fruit yield and fruit quality parameters were measured as performance indicators. Biochar increased the green biomass, but it did not significantly affect yield or most quality parameters, apart from potassium content in ripe fruits. These results suggest that biochar has great potential as a peat alternative material and plant growth promoter, but no ability to improve tomato yield, under nutritional stress.

Estimating transpiration rates of hydroponically-grown paprika via an artificial neural network using aerial and root-zone environments and growth factors in greenhouses

Abstract

Environmental and growth factors are important variables that affect the transpiration rate of crops, but due to their complex nature, it is difficult to systematically use all these factors to estimate transpiration rates. Application of artificial neural networks (ANNs) can be an efficient way of deriving meaningful results from complex nonlinear data. The objectives of this study were to estimate transpiration rates using an ANN, to compare these estimations with the Penman–Monteith (P–M) equation, and to analyze the estimation accuracy according to cultivation period. Paprika (Capsicum annuum L. cv. Scirocco) was cultivated for two cropping periods in a year. Environmental factors were collected every minute and leaf area index (LAI) as a growth factor was measured every 2 weeks. An ANN consisting of an input layer using eight environmental and growth factors, five hidden layers, and an output layer for transpiration rate was constructed. The estimation accuracy in the ANN was higher than the P–M when using aerial environmental factors, but it was further increased by adding root-zone factors. Using daily average data, ANN accuracy was higher for longer cultivation periods and accompanying data. R² values were 0.88 and 0.73 in the ANN and P–M for one year, whereas they were 0.84–0.93 and 0.79–0.83 for the individual seasons, respectively. The accuracy of the ANN tended to increase when the time step (data-averaging time unit) decreased to 10 min and there was no significant difference over 10 min. Using 10-min average data, the ANN showed high accuracies with R² = 0.95–0.96 and root mean square error = 0.07–0.10 g m⁻² min⁻¹, regardless of cultivation period and season. Therefore, it was confirmed that the ANN could accurately estimate transpiration rates at specific times using the data collected from the entire cultivation period. This approach may be useful for developing irrigation strategies by estimating the transpiration rates of crops grown in soilless cultures.

Harvest strategies to maximize the annual production of bioactive compounds, glucosinolates, and total antioxidant activities of kale in plant factories

Abstract

Since kale (Brassica oleracea L. var. acephala) is one of the healthiest vegetables, its cultivation is increasing for either fresh consumption or as a source for functional foods and nutraceuticals. Plant factories are able to control the environment and trigger the accumulation of bioactive compounds with a stable supply by systematic cultivation methods. The objectives of this study were to evaluate the changes in the total phenolic compounds (TPCs), total flavonoid compounds (TFCs), glucosinolates (GLSs), and antioxidant capacity of kale in a plant factory and to determine an optimal harvest time for the maximum annual production. Two cultivars, namely ‘Manchoo collard’ and ‘Jangsoo collard’, were cultivated in a plant factory and thinned to avoid mutual shading. Both cultivars were harvested every week from 14 to 49 days after transplanting (DAT). The fresh weight (FW), dry weight (DW), projected leaf area (PLA), TPCs, TFCs, GLSs, and antioxidant capacity of both plants were measured every week. The annual production was calculated as follows: DW × the concentration × planting density × cultivation cycles per year. The optimal harvest time was determined based on the continuous phase of the production by modeling. The FW and DW of both cultivars exponentially increased, but the PLA hardly increased at 35 DAT. The TPCs, TFCs, and antioxidant capacity fluctuated or slightly changed, but the amount of substance per plant gradually increased. Their annual production increased with increasing harvest time, and only the production of TPCs in ‘Manchoo collard’ showed a local maximum when harvested at 35–42 DAT. Glucoiberin, sinigrin, and glucobrassicin were the major components of GLSs in both cultivars, and their contents fluctuated. The concentration of total GLSs was the highest at 42 DAT. Additionally, the annual production of the total and major GLSs showed the same results as the TPCs, TFCs, and antioxidant capacity. From the results, the optimum harvest time for production was determined to be 42 DAT.

Discovery of PTE -1, Tourist -like miniature inverted repeat transposable element (MITE), and its activation in transgenic Brassica rapa ssp. pekinensis plants

Abstract

Miniature inverted-repeat transposable elements (MITEs) are class II, non-autonomous DNA transposons that occupy a large portion of the genome, most in an inactive state. Because transposition of MITEs can have a broad impact on the structure and function of the genome, it is important to identify activated MITEs and analyze their propensity for transposition. However, to date the activity of only a few MITEs has been analyzed. In this study, MITE activation during the transformation processes in Chinese cabbage was analyzed by using next-generation sequencing. Using genome wide analysis, we found PTE-1 was activated during the transformation process. The active transposition of PTE-1 was analyzed by PCR amplification. We determined the sequence of PTE-1 by cloning the PCR products. Based on its target site duplications sequence and terminal inverted repeats structure, we inferred that the element belongs to the Tourist family. The characteristics of PTE-1, including structure and copy number, were identified by bioinformatics approaches. The results suggest that PTE-1 activation could be induced by the transformation process and reveal the first detection of activated MITE in tissue culture derived from Brassica rapa plants.

Foliar application of biostimulants affects physiological responses and improves heat stress tolerance in Kimchi cabbage

Abstract

This study investigated the effects of foliar applications, such as brassinosteroid (BR), methyl jasmonate (JA), salicylic acid (SA), and sodium nitroprusside (SNP), on the growth, yield, photosynthetic characteristics, and antioxidant enzyme activity of Kimchi cabbage (Brassica rapa L. ssp. pekinensis) exposed to heat stress. Kimchi cabbages were grown in extreme weather growth chambers under controlled conditions (air temperature, relative humidity, and solar radiation of the Daegwanryeong region, 37° 40′ N, 128° 32′ E). At 18 days after transplanting, Kimchi cabbages were treated with foliar application of biostimulants (vs. non-sprayed control) and exposed to heat stress (air temperature 30/25 °C) and mean daily air temperature under normal conditions (21.2 ± 1.6 °C day/night, respectively) for 5 days. The foliar application concentrations were 50, 100, and 200 nM BR; 50, 100, and 200 μM JA; 1, 2, and 4 mM SA; and 0.25, 0.50, and 1.00 mM SNP. At 38 days after foliar application, the shoot fresh weight of Kimchi cabbages treated with 200 nM BR was 2123 versus 1422 g plant⁻¹ (control). The head weight and yield were the greatest with 2 mM SA treatment, which produced 3806 versus 2184 kg ha⁻¹ (control). Heat stress induced a low photosynthetic rate in Kimchi cabbage, while foliar application of biostimulants enhanced photosynthesis recovery. During the 3 days after heat stress, catalase and peroxidase enzyme activities of Kimchi cabbage increased by 1.76- to 2.08-fold on average compared to the control. Results indicated that foliar application of biostimulants reduced physiological damage and enhanced the activity of the antioxidant enzymes, thereby improving heat stress tolerance in Kimchi cabbage.

Influence of physical properties of peat-based potting mixes substituted with parboiled rice hulls on plant growth under two irrigation regimes

Abstract

This study was conducted to investigate the effects of physical properties of peat-based substrate mixtures partially substituted with parboiled rice hulls (PRH) on plant growth and performance. Thirteen substrate mixtures were formulated by substituting 0, 20, 30, 40, 50, 60, or 70% peat with either parboiled ground rice hulls (GRH) or whole rice hulls (WRH) (by volume) in commercial potting mix (CPM) containing 70% peat, 20% perlite, and 10% vermiculite. All substrate mixtures consisted of mainly medium-sized (2.0–0.25 mm) particles. However, regardless of the mixing ratio, GRH significantly increased the medium-sized particles especially with diameters of 2.0–0.71 mm, while WRH increased both the medium- and coarse-sized (> 2.0 mm) particles. A higher mixing ratio of PRH increased air space and decreased container capacity but to a greater extent by WRH compared to GRH. Similarly, bulk density was increased with a higher mixing ratio of both types of PRH, but to a greater degree by GRH. Total porosity of GRH-containing substrates was similar to that of CPM within the range of 30–70%. The substrate mixtures containing PRH did not have the same physical properties as the CPM at any mixing ratio, but the values of some GRH-containing mixtures were within or close to the suggested ranges for greenhouse substrates. Considering the maximum substitution of PRH for peat, the substitution with 40% GRH (GRH-40) was selected for a plant growth study in comparison to CPM. Petunia (Petunia × hybrida) ‘Easy Wave Neon Rose’ and zinnia (Zinnia elegans) ‘Benary’s Giant Golden Yellow’ were grown in pots containing CPM and GRH-40 at two irrigation levels: high (25–30%, by volume) and low (20–25%). Overall, shoot DW of both plant species was reduced in GRH-40, but root DW was maintained similar to those in CPM. The low irrigation level more significantly reduced shoot DW of petunia grown in CPM than in GRH-40, relative to their counterparts with the high irrigation level (20 and 7%, respectively); however, root growth of plant species grown in GRH-40 was either maintained or tended to be maintained even at the low irrigation level compared to their high irrigation counterparts. The water use efficiency of plants grown in GRH-40 was not significantly different from those in CPM regardless of irrigation level. These results indicate that GRH-40 provides desirable physical properties and water release characteristics, allowing more available water for plants under low irrigation levels than CPM. We concluded that substituting peat with 40% GRH in a commercial potting mix is a sustainable approach to produce petunia and zinnia.

Supplemental potassium mediates antioxidant metabolism, physiological processes, and osmoregulation to confer salt stress tolerance in cabbage ( Brassica oleracea L.)

Abstract

Soil salinity is one of the severe threats of climate change that inflicts heavy losses to vegetable production. Potassium (K) has been considered essential approach against abiotic stresses in food crops, however, understanding of K regulated mechanisms for inducing tolerance to NaCl stress in cabbage (Brassica oleracea L.) plants is, still elusive. Here, we report the supplemental K effects on antioxidant defense system and physiological processes that may influence the cabbage production under saline conditions. Initially, cabbage varieties (‘Stone Head’, ‘Golden Acre’, ‘9j-940’, ‘Beauty Ball’, ‘Green Ball’, ‘Green Rise’, ‘Marco F-1’) were tested under NaCl stress (50, 100, 150, and 200 mM) for their higher growth, vigor index and mineral contents. The identified cabbage var. salt-tolerant, cv. Beauty Ball (BB) and salt-sensitive cv. Green Ball (GB) were further exposed to foliar K (5 and 10 mM solutions of KNO₃) under the same NaCl regimes. NaCl stress markedly inhibited photosynthetic efficiency, water status and chlorophyll pigments, thereby, resulted in reduced dry biomass of both varieties. Nevertheless, exogenous K spray at 10 mM caused positive gain in leaf water relations, chlorophyll contents in both cabbage varieties. The ameliorative impacts of K were more pronounced in salt-tolerant cv. BB as compared to salt-sensitive cv. GB in terms of higher accumulation of total soluble proteins, total free amino acids, proline contents, upregulated antioxidant activities and enhanced gas exchange characteristics. Hence, improvement in growth and K⁺/Na⁺ ratio of cabbage plants by foliar K application (10 mM) were related to up-regulation of physiological and biochemical mechanisms under saline conditions.

Effects of elevated ozone on physiological, biochemical and morphological characteristics of eggplant

Abstract

Air pollutants are emitted from various anthropogenic sources into the atmosphere. Especially, ozone (O₃) has become a critical problem since the average O₃ concentration is increasing every year by about 0.5–2% across the world. O₃ in the air affects plant growth because it mainly passes through the stomata of leaves into plants. This experiment was designed to identify the physiological, morphological, and biochemical responses of plants to O₃. For the purposes of this study, eggplant (Solanum melongena L.), which is one of the most well-known crops produced in the world, was used. Eggplants were continuously subjected to 110 nmol mol⁻¹ for 25 days using the phytotron. Following O₃ treatment, the growth and biomass of the eggplant were reduced, and the photosynthetic rates were lower than those of the controls. In contrast, water use efficiency increased progressively on the leaves of the eggplant. Initial visible injures were observed at 15 days after O₃ treatment. Stomatal density was reduced in response to the O₃ treatment. With regard to biochemical responses, malondialdehyde content and relative ion leakage were higher than those of the control. Superoxide and hydrogen peroxide accumulation was observed on the leaf surface after 25 days of O₃ treatment. These observations indicate that treatment with 110 nmol mol⁻¹ O₃ had negative effects on the physiological, morphological, and biochemical activities of eggplant. Further studies investigating the damage caused by exposure to different concentrations of O₃ and for different periods of time are required.

Evaluation of sweet cherry fruit quality after short-term storage in relation to the rootstock

Abstract

Fruits of the sweet cherry cultivar ‘Regina’ collected from trees growing on seven rootstocks were stored in a cold room at 2 °C with a normal (NA) and controlled atmosphere (15% and 20% CO₂ and 5% O₂—CA1 and CA2) for 2 weeks. The rootstocks on which the trees grew and the storage conditions significantly affected all fruit parameters tested during both years of the experiment. Fruit from Damil rootstock exhibited higher mean firmness than fruit from Colt rootstock. The effect of rootstocks on the value of soluble solids content (SSC) varied, wherein the fruits from Tabel Edabriz and Damil were characterized by high SSC mean content. The organic acids content (TA) was significantly lower after storage than during harvest time. Fruits from Tabel Edabriz trees were characterized by faster ripening, as was evident by the higher SSC to TA ratio. The amount of mass lost depended significantly and only on the storage conditions—sweet cherries from both CA combinations had the lowest mass losses. The percentage of fruits showing disease symptoms was largely dependent on the weather conditions in the orchard the year before the fruit harvest, as well as atmosphere composition and RH during fruit storage. Cold storage conditions with a high (20%) CO₂ content are recommended for the short-term storage of sweet cherry fruits because they preserve fruit quality parameters: a low decrease in firmness, maintenance of a high SSC/TA ratio, a low percent of fungal infections, and good preservation of green color in the peduncle.