Root-zone Temperature Research Articles

Supraoptimal Root-zone Temperatures Affect Dahlia Growth and Development

Dahlia (Dahlia ×hybrida) is an important floriculture crop that has gained popularity in recent years. Greenhouse growers have recently reported a phenomenon known as “dahlia decline,” that can affect potted dahlias in greenhouse production. The crop exhibits graying foliage, root decline, and plant death, and the phenomenon has reportedly caused partial or total crop loss and has no known initiating factor. We hypothesized that plant exposure to supraoptimal root-zone temperatures (RZTs) during production may decrease dahlia root quality, especially above 40 °C and could initiate dahlia decline. Because there is a lack of understanding on how supraoptimal RZT may impact dahlia growth and development, experiments were conducted to evaluate the effects of supraoptimal RZTs on seven dahlia cultivars in Spring 2019 and 2020. Dahlias were grown for 4 to 5 weeks in the greenhouse and then root zones were exposed to ≈22 (control), 35, 40, 45, or 50 °C using a water bath. Root quality was rated before treatment and rated weekly after the hot water bath treatment, along with vegetative growth parameters for 4 weeks. In both years, significant decline in root ratings were observed. ‘XXL Veracruz’ and ‘XXL Sunset’ average root ratings decreased after a 45 and 50 °C treatments in year 2 and both cultivars demonstrated increased root rating averages by 3 weeks after treatment. Cultivars exhibited a significant increase in root rating in the final observations when compared with root ratings taken 1 week posttreatment even if the initial decline after treatment was not significant. Overall plant height was significantly impacted, resulting in shorter heights in both years for all cultivars as treatment temperatures increased to 50 °C in comparison with the control and 35 °C, and a few cultivars exhibited significantly shorter height at 40 and 45 °C. Ultimately, our research did not show typical plant responses that were consistent with reported dahlia decline, but we were better able to characterize dahlia response to supraoptimal RZT.

Elevated root-zone temperature promotes the growth and alleviates the photosynthetic acclimation of cucumber plants exposed to elevated [CO2

Greenhouse cultivation forms a relatively closed environment for heat preservation in winter, which inevitably leads to a lack of atmospheric CO2 concentration ([CO2]), and thus low [CO2] level has become a limiting factor for the photosynthesis and growth of greenhouse vegetables. Most cucurbits and solanaceous vegetables are sensitive to low temperature, but it is difficult to keep the optimum root-zone temperature (RZT) for them in greenhouse soil cultivation in winter. Therefore, low RZT is another limiting factor for greenhouse vegetables growth in winter. This study investigated the effects of [CO2], RZT, and their interactions on cucumber yield, growth, photosynthesis, and photosynthate allocation in four open-top chambers for a growth period of 73 days after transplanting. We found elevated RZT increased yield and total dry weight of cucumber plants to a greater extent than elevated [CO2]. We also observed long-term elevated [CO2] limited the increase of net photosynthetic rate (Pn) and decreased the stomatal conductance (Gs) and transpiration rate (Tr) of cucumber plants at ambient RZT, resulted in the photosynthetic acclimation, as illustrated by the significant reduction of nitrogen concentration and the increased concentrations of soluble sugar and starch in leaves. In comparison, the combination of elevated [CO2] and RZT decreased the concentrations of soluble sugar and starch and maintained the nitrogen concentration in leaves, which caused a higher Pn, Gs and Tr. Meanwhile, more soluble sugar and starch were allocated from leaves to roots due to the higher root respiratory under elevated [CO2] and RZT treatment. Moreover, elevated RZT could facilitate the mineral nutrients absorption by roots and the upward transportation because of the larger root system and higher Tr. Therefore, elevated RZT could offset the decrease in Pn and improve Gs and Tr under elevated [CO2], which indicated an alleviation of the photosynthetic acclimation of cucumber plants exposed to long-term elevated [CO2].

Heat transfer assessment of multi-tier chilling pipes for root zone cooling system under crop protection structure in the tropics

Root zone cooling technique has become an alternative cultivation method for temperate crops production in the tropics instead of cooling the aerial environment of the greenhouse. In this experiment, the root zone cooling system was incorporated with a multi-tier crop cultivation structure. This structure consisted of five tiers arranged in an A-shape design and was placed under an open rain shelter, thus, left it to undergo fluctuating environment temperature. There were five pillow polybags inserted with cocopeat and were placed on the structure. Each pillow polybag consisted of a single pipe that was buried inside the growth media located near the root zone area. This pipe that was connected to the chilled system acted as a cooling agent in controlling the growth media temperature. The objective of the study was to evaluate the Root Zone Cooling (RZC) system performance in distributing and controlling water-dissolved nutrient temperatures to meet crop-root requirement needs. From the experiment conducted, it was found that there was no significant difference between root zone temperature at different levels and lengths on multi-tier structure. The chilling pipes was able to distribute the temperatures to meet crop-root requirement needs along the multi-tier structure.

Environmental and Cultivation Factors Affect the Morphology, Architecture and Performance of Root Systems in Soilless Grown Plants

Soilless culture systems are currently one of the fastest-growing sectors in horticulture. The plant roots are confined into a specific rootzone and are exposed to environmental changes and cultivation factors. The recent scientific evidence regarding the effects of several environmental and cultivation factors on the morphology, architecture, and performance of the root system of plants grown in SCS are the objectives of this study. The effect of root restriction, nutrient solution, irrigation frequency, rootzone temperature, oxygenation, vapour pressure deficit, lighting, rootzone pH, root exudates, CO2, and beneficiary microorganisms on the functionality and performance of the root system are discussed. Overall, the main results of this review demonstrate that researchers have carried out great efforts in innovation to optimize SCS water and nutrients supply, proper temperature, and oxygen levels at the rootzone and effective plant–beneficiary microorganisms, while contributing to plant yields. Finally, this review analyses the new trends based on emerging technologies and various tools that might be exploited in a smart agriculture approach to improve root management in soilless cropping while procuring a deeper understanding of plant root–shoot communication.

The Potential Effect of Elevated Root Zone Temperature on the Concentration of Chlorogenic, Caffeic, and Ferulic acids and the Biological Activity of Some Pigmented Solanum tuberosum L. Cultivar Extracts

Without a doubt, potatoes play a vital food and nutrition security role in the world as more than a billion people consume this vegetable. Furthermore, the polyphenolic constituents of pigmented potato cultivars and their associated health benefits have been reported. However, the antioxidant, anticancer, and antimycobacterial activity of pigmented cultivars are scanty. Therefore, the present study explores the phenolic acids and biological activities of cv. Salad Blue (SB) and non-pigmented control (BP1) extracts. The antiproliferative activity of S. tuberosum L. against human hepatocellular carcinoma (HepG2) was investigated, as well as the ability to inhibit Mycobacterium smegmatis. Chlorogenic acid was the most prominent phenolic acid in both treatments as well as cultivars. In the current trial, 24 °C significantly increased chlorogenic acid in cv. SB and BP1. Ethanolic extracts of all the samples showed no activity at the highest test concentration of 1000 μg/mL (ciprofloxacin MIC of 0.325 μg/mL) against M. smegmatis. The antiproliferative activity of the tuber samples against HepG2 liver cells had IC50 values ranging between 267.7 ± 36.17 μg/mL and >400 μg/mL. Since the health benefits of these cultivars are highly valued, the present study provides useful information for future oncology studies, for human nutrition, as well as for how these underutilized cultivars can be fortified to improve their health benefits.

Dendrometer measurements of arctic-alpine dwarf shrubs and micro-environmental drivers of plant growth - Dataset from long-term alpine ecosystem research in central Norway

Here, we present fine-scale measurements of stem diameter variation from three common arctic-alpine dwarf-shrub species monitored in two mountain regions of Central Norway. All three species (Betula nana, Empetrum nigrum ssp. hermaphroditum, and Phyllodoce caerulea) are abundant within the studied regions and highly important contributors to potential future arctic-alpine vegetation shifts. A profound understanding of their radial growth patterns therefore has the potential to yield crucial information regarding climate-growth relations within these ecosystems. We used high-resolution dendrometers (type DRO) to monitor 120 specimens, taking measurements near the shoot base of one major horizontal stem. Along with the shrub growth measurements, we measured on-site micro-environmental data at each studied site, including shoot zone and root zone temperatures as well as soil moisture. All data were recorded at an hourly scale and are presented as daily mean values. The monitoring period spanned five full years (2015 - 2019), with additional data from 2014 and 2020. Data were collected within one of the most continental climate regions of Europe, the Vågå/Innlandet region, and in the oceanic climate region Geiranger/Møre og Romsdal, spanning a steep climate gradient over just ~100 km horizontal distance. Both study regions are characterized by steep elevational gradients and highly heterogeneous micro-topography. The studied sites were chosen to represent these natural conditions using the transect principle. The collection of our original data is subject of our long-term alpine ecosystem monitoring program since 1991, from which numerous publications function as the basis for a recent project on the use of dendrometer data in alpine ecosystem studies.

Efficacy of Root Zone Temperature Increase in Root and Shoot Development and Hormone Changes in Different Maize Genotypes

In the context of global warming, the effects of warming in the root zone of crops on maize seedling characteristics deserve research attention. Previous studies on the adaptive traits of dryland maize have mainly focused on soil moisture and nutrients, rather than analyzing potential factors for the adaptive traits of root zone warming. This study was conducted to investigate the effects of different root zone warming ranges on the agronomic traits, hormones, and microstructures of maize seedling roots and leaves. The results showed that minor increases in the root zone temperature significantly enhanced maize seedling growth. However, when the temperature in the root zone was excessive, the stem diameter, root surface area, root volume, total root length, dry matter accumulation, and root/shoot biomass of maize seedlings sharply decreased. Under high temperature stress in the root zone, the root conduit area; root stele diameter; root content of trans-zeatin (ZT), gibberellin A3 (GA3), and indoleacetic acid (IAA); leaf thickness; upper and lower epidermis thickness; and leaf content of ZT and GA3 were significantly decreased. The hormone content and microstructure changes might be an important reason for root growth maldevelopment and nutrient absorption blockage, and they also affected the leaf growth of maize seedlings. Compared with the ‘senescent’ maize type Shaandan 902 (SD902), the plant microstructure of the ‘stay-green’ maize type Shaandan 609 (SD609) was less affected by increased temperatures, and the ability of the root system to absorb and transport water was stronger, which might explain its tolerance of high temperature stress in the root zone.

Studies of Vegetative Growth, Inflorescence Development and Eco-Dormancy Formation of Abscission Layers in Streptocarpus formosus (Gesneriaceae)

Streptocarpus formosus (Hilliard & B.L. Burtt) T.J. Edwards is a flowering herbaceous perennial indigenous to South Africa and is part of the rosulate group of herbaceous acaulescent plants within the Gesneriaceae family. According to the National Assessment database for the Red List of South African Plants version 2020.1., the plant is listed as rare. The ornamental use of S. formosus has untapped commercial potential as a flowering indoor pot plant, an outdoor bedding plant for shade and as a cut flower for the vase, all of which are limited by a five-month eco-dormancy period during the late autumn and all through the cold season in the short-day winter months. Viable commercial production will require cultivation techniques that produce flowering plants all year round. This study investigated the effectiveness of applying root zone heating to S. formosus plants grown in deep water culture hydroponics during the eco-dormancy period in preventing abscission layer formation and in encouraging flowering and assessed the growth activity response of the plants. The experiment was conducted over eight weeks during the winter season in the greenhouse at Kirstenbosch Botanical garden in water reservoirs, each maintained at five different experimental temperature treatments (18, 22, 26—control, 30 and 34 °C) applied to 10 sample replicates. The results showed that the lowest hydroponic root zone temperature of 18 °C had the greatest effect on the vegetative growth of S. formosus, with the highest average increases in fresh weight (1078 g), root length (211 cm), overall leaf length (362 cm) and the number of newly leaves formed (177 = n), all noted as statistically significant when compared with the other water temperature treatments, which yielded negative results from reduced vegetative growth. Findings from the study also revealed that while all heated solutions significantly prevented the formation of abscission layers of S. formosus, they had a less significant effect on inflorescence formation, with only 18 °C having the greatest positive effect on flower development.

Optimum strategies for the control of root-zone temperature to promote early-stage growth of chili pepper in soilless culture using an intelligent approach

Optimum strategies for the control of root-zone temperature to promote early-stage growth of chili pepper in soilless culture using an intelligent approach

From Standard Weather Stations to Virtual Micro-Meteorological Towers in Ungauged Sites: Modeling Tool for Surface Energy Fluxes, Evapotranspiration, Soil Temperature, and Soil Moisture Estimations

One of the benefits of training a process-based, land surface model is the capacity to use it in ungauged sites as a complement to standard weather stations for predicting energy fluxes, evapotranspiration, and surface and root-zone soil temperature and moisture. In this study, dynamic (i.e., time-evolving) vegetation parameters were derived from remotely sensed Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and coupled with a physics-based land surface model (tin-based Real-time Integrated Basin Simulator (tRIBS)) at four eddy covariance (EC) sites in south-central U.S. to test the predictability of micro-meteorological, soil-related, and energy flux-related variables. One cropland and one grassland EC site in northern Oklahoma, USA, were used to tune the model with respect to energy fluxes, soil temperature, and moisture. Calibrated model parameters, mostly related to the soil, were then transferred to two other EC sites in Oklahoma with similar soil and vegetation types. New dynamic vegetation parameter time series were updated according to MODIS imagery at each site. Overall, the tRIBS model captured both seasonal and diurnal cycles of the energy partitioning and soil temperatures across all four stations, as indicated by the model assessment metrics, although large uncertainties appeared in the prediction of ground heat flux, surface, and root-zone soil moisture at some stations. The transferability of previously calibrated model parameters and the use of MODIS to derive dynamic vegetation parameters enabled rapid yet reasonable predictions. The model was proven to be a convenient complement to standard weather stations particularly for sites where eddy covariance or similar equipment is not available.

TMT-Based Quantitative Proteomic Revealed Metabolic Changes of Jasmonic Acid in Regulating the Response of Malus baccata (L.) Borkh. Roots to Low Root-Zone Temperature

Malus baccata (L.) Borkh. is widely used as an apple rootstock in northern China. Previous studies have shown that jasmonic acid (JA) can alleviate the oxidative damage in M. baccata roots under low root-zone temperature (LT), yet the regulatory mechanism is unclear. To uncover the mechanism of JA in regulating the response of roots to LT, the differential expression of proteins was profiled using TMT combined with MRM. Of the 4979 proteins quantified, 403 differentially expressed proteins (DEPs) responded to the LT treatment and 264 DEPs responded to the JA + LT treatment. A bioinformatic analysis showed that protein processing in the endoplasmic reticulum, alpha-linolenic acid metabolism, and secondary metabolites play key roles in the regulation of JA in M. baccata roots exposed to LT. In addition, proteins involved in the stress response, such as peroxidases and calcium-dependent protein kinase, also participated in the regulation of JA. The quantitative data were then confirmed using MRM, thereby proving that the TMT results were reliable. The results can provide theoretical reference for the regulation of apple roots under low-temperature stress.

EFFECT OF ROOT ZONE TEMPERATURE ON NUTRIENT UPTAKE IN SOILLESS CULTIVATION SYSTEMS

The main objective of this research is to evaluate the Effect of root zone temperature on nutrient uptake in soilless cultivation systems and to obtain the best reused rate for nutrients after treatment and Fertigation management in closed soilless culture systems and Fertilizer calculator for each element’s at long time of plant. The experiment was carried out in a multi-Spanish agricultural greenhouse covered with polyethylene film and aspects covered with fiberglass. There is a cooling system for evaporation (pad and fan), a heating system roots and a control in the irrigation and fertilization process. Agricultural soil is composed of bitmous, perlite and vermiculite. The obtained results indicated that the closed soilless culture systems with intermittent irrigation and heating the root zone (T1) the best from than all treatments systems closed soilless culture systems with intermittent irrigation (T2), closed soilless culture systems with irrigation once and heating the root zone (T3) and closed soilless culture systems with irrigation once (T4) in terms of uptake nutrients (Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca) and Magnesium (Mg) and The best absorption of water was the treatment of the closed soilless culture systems with intermittent irrigation and heating the root zone and the best growth parameters which include plant height, internode length, stem diameter, number of leaves, leaf area, mass of fruit and yield was the treatment of the closed soilless culture systems with intermittent irrigation and heating the root zone.

Effect of the Root Zone Temperature and Salt Stress on Plant Growth, Main Branches and some other Chemical Characteristics of Tomato Fruit Solanum lycopersicum L. cv. memory

In order to study the impact of salt stress (0, 1.5, 3 and 6) ds.m-1 in nutrient’s solution on tomato plant (Solanum lycopersicum L. cv. memory) at different root zone temperature [low (20°C), medium (25°C) and high (30°C)], an experiment was carried at Department of Horticultural, Ferdowsi University of Mashhad, Islamic Republic of Iran. The result showed that low and high root zone heating decreased leaf area, total sugar and phenol content compared to root zone temperature 25°C (optimum), while main branches number, pH, E.C. and anthocyanin of fruit ,increased at high root zone temperature compared to low root zone temperature. Flavonoid increased under the root zone temperature of 20°C in comparison with temperatures 25 and 30°C, and stem diameter was not affected by root zone heating. Furthermore, salt stress at the level of 3 ds.m-1 increased stem diameter, total sugar, pH and EC of fruit, leaf area and phenol content, whereas salt stress at a high level (6 ds.m-1) increased flavonoid content. Besides, anthocyanin content decreased in control and salt stress at 6 ds.m-1 when compared to salt stress at 3 ds.m-1.

Plant Factories Are Heating Up: Hunting for the Best Combination of Light Intensity, Air Temperature and Root-Zone Temperature in Lettuce Production.

This study analyzed interactions among photon flux density (PPFD), air temperature, root-zone temperature for growth of lettuce with non-limiting water, nutrient, and CO2 concentration. We measured growth parameters in 48 combinations of a PPFD of 200, 400, and 750 μmol m–2 s–1 (16 h daylength), with air and root-zone temperatures of 20, 24, 28, and 32°C. Lettuce (Lactuca sativa cv. Batavia Othilie) was grown for four cycles (29 days after transplanting). Eight combinations with low root-zone (20 and 24°C), high air temperature (28 and 32°C) and high PPFD (400 and 750 μmol m–2 s–1) resulted in an excessive incidence of tip-burn and were not included in further analysis. Dry mass increased with increasing photon flux to a PPFD of 750 μmol m–2 s–1. The photon conversion efficiency (both dry and fresh weight) decreased with increasing photon flux: 29, 27, and 21 g FW shoot and 1.01, 0.87, and 0.76 g DW shoot per mol incident light at 200, 400, and 750 μmol m–2 s–1, respectively, averaged over all temperature combinations, following a concurrent decrease in specific leaf area (SLA). The highest efficiency was achieved at 200 μmol m–2 s–1, 24°C air temperature and 28°C root-zone temperature: 44 g FW and 1.23 g DW per mol incident light. The effect of air temperature on fresh yield was linked to all leaf expansion processes. SLA, shoot mass allocation and water content of leaves showed the same trend for air temperature with a maximum around 24°C. The effect of root temperature was less prominent with an optimum around 28°C in nearly all conditions. With this combination of temperatures, market size (fresh weight shoot = 250 g) was achieved in 26, 20, and 18 days, at 200, 400, and 750 μmol m–2 s–1, respectively, with a corresponding shoot dry matter content of 2.6, 3.8, and 4.2%. In conclusion, three factors determine the “optimal” PPFD: capital and operational costs of light intensity vs the value of reducing cropping time, and the market value of higher dry matter contents.

Highly reflective algae for enhancing climate change resilience in rice production

AbstractThere is an urgent need for enhancing climate change resilience in rice production. Here, we report a reflective algal mulching‐based culture practice to attain a simple and low‐cost biological method for enhancement of climate change resilience. The dense mulching of Rhizoclonium sp. in field water highly reflected sunlight in the visible and infrared regions, thus significantly decreasing the root zone temperature, and significantly and simultaneously mitigated CO2, CH4, and N2O emissions through gas retention and removal in the field water layer, as well as reducing gas production. The algae could also enhance rice growth and soil fertility.

Effects of Root Zone Temperature Increase on Physiological Indexes and Photosynthesis of Different Genotype Maize Seedlings

This experiment investigated the effects of different degrees of warming of the root zone on the antioxidant enzyme activity and malondialdehyde (MDA) content, chlorophyll fluorescence parameters, and photosynthetic physiological parameters of maize (Zea mays L.) seedling roots. Different genotypes of maize types SD609 (Stay-green Maize type) and SD902 (senescent type) were used as test materials in the test and the test set three root zone temperatures (24, 30, and 36°С). The results showed that properly increasing the root zone temperature could significantly promote the growth of maize seedlings, increase the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and actual photochemical efficiency (ΦPS) electron transfer rate (ETR), photochemical quenching coefficient (qP), increase leaf photosynthesis and transpiration rate. However, when the root zone temperature was too high, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in the roots of maize seedlings would be significantly reduced, and the content of malondialdehyde (MDA) would be increased. This lead to excessive accumulation of reactive oxygen, which affects the functions of root system absorption, synthesis, transportation, etc., leading to reduced leaf enzyme activity, damaged to the PSII reaction center, and reduced photosynthetic rate. Among them, the Stay-green Maize type SD609 had a significantly smaller change than the aging type SD902. Under high temperature stress in the root zone, the relatively high antioxidant enzyme activity, better stability of the PSII reaction center, and photoprotection mechanisms of SD609 were the physiological basis for maintaining a stable photosynthetic rate and resisting high temperature in the root zone. PSII reaction center damage and relatively low non-photochemical quenching coefficient may be an important factor for non-stomatal limitation of SD902.

The role of root zone temperature on physiological and phytochemical compositions of some pigmented potato (Solanum tuberosum L.) cultivars

A greenhouse study was conducted to evaluate the effects of three root zone temperatures (20, 24 and 28°C) on growth and chemical compositions in seed mini tubers of four pigmented Solanum tuberosu...

Numerical and Experimental Analyses on Root Zone Temperature in Aeroponic Cultivation Box

Vegetable growth requires a relatively stable environment for the root zone. If the temperature in root zone environment is optimal, the aeroponic cultivation will be energy-efficient, and the aeroponic vegetables will grow well at high, normal, or low temperature. By computational fluid dynamics (CFD), this paper numerically simulates the root zone temperature of lettuce in the aeroponic cultivation box, after the box was sprayed with nutrient solutions of different temperatures. Then, the root zone environments of aeroponic lettuce were monitored through experiments at three different temperatures: high temperature, normal temperature, and low temperature. Through comparison, it was learned that the error between the simulated and measured values at each point was smaller than 1.35℃; the maximum error at a single point was within 7.4%; overall, the mean relative error was merely 5.8%. The results prove that the proposed CFD simulation model is reasonable and effective. Our research provides a theoretical reference for optimizing the root zone temperature, regulating the spray of nutrient solutions at different temperatures, and building an energy-efficient efficient aeroponic cultivation system.

An Alternative Healing Method for Grafted Tomato Transplants: The Effect of Light Exclusion and Substrate Temperature on Plant Survival and Growth

The use of tomato (Solanum lycopersicum) grafting is gaining traction across the United States, but small-scale growers face the challenge of creating optimum postgrafting healing conditions. The practice of blocking light for a period of 2 to 4 days while maintaining high humidity is commonly recommended for healing grafted tomato transplants; however, research is exploring alternatives to this practice. The present study investigated a low-input healing method for grafted tomato transplants with a specific focus on light and the use of propagation heat mats to regulate substrate and healing chamber air temperatures during the 7-day healing process. We hypothesized that 4 days of light exclusion and the use of propagation heat mats would improve grafted tomato transplant survival and growth. ‘Cherokee Purple’ was used as the scion and ‘RST-04-106-T’ was used as the rootstock. The whole plot factor was heat [propagation mats set at 80 °F (heat) or no propagation mat (no heat)] and the subplot factor was light exclusion (0, 4, or 6 days of dark). The highest survival rate among treatments was 97% in 0 days of dark with no heat treatment; survival decreased to 84% in 4 and 6 days of dark with no heat treatments. The plant survival rate was 96% with 0 days of dark and heat treatment; however, the survival rates were 63% and 45% for the 4- and 6-day dark treatments, respectively. The scion stem diameter was largest for transplants grown in 0 days of dark, but there was no difference in stem diameter due to heat treatments. There were no differences among scion or rootstock biomasses due to heat or light treatments. These results demonstrate that propagation mats set at 80 °F to regulate the substrate temperature were detrimental to grafted transplant survival under extended periods of light exclusion. However, this finding creates the basis to explore lower levels of substrate temperature modification. Our work also indicates that light exclusion may not be necessary for healing grafted tomato plants regardless of root-zone temperature treatments. Future work should examine the interactions of various substrate and air temperatures under full light conditions and their effects on grafted tomato transplant survival and growth. This work contributes to the ongoing research of how to optimize low-input healing methods that may be readily adopted by small-scale tomato growers.

An alternative health crop for South Africa: Purple potato mini tuber production as affected by water and nutrient stress

Food security in South Africa ranks as one of the top ten priorities in the country. Potato is a fundamental staple food crop in South Africa, providing essential nutrition. While there are several cultivars currently in production for the potato market, there is a need to explore cultivars that are available, but not utilised within the country. Pigmented potatoes are not regarded as high value on the South African market;however,yield prospects as well as health-promoting benefits could have a positive contribution on the South African Gross Domestic Product (GDP) and on the population’s health. Potato cultivar (cv.) Salad blue(SB)seems to be a drought-tolerant crop with the ability to produce reasonable yields under severe environmental conditions. In order to promote cv. SB as a possible food security option for South Africa, there is a critical need for empirical information, describing some basic horticultural as well as biochemical information and vitamin C presence. This study investigated the potential of pigmented potato SB tubers as an alternative to high yielding white potato for the South African market.Tubers of Solanum tuberosum cv. BP1 and SB, were used for this research.The high amounts in phenolic compounds in SB can be considered to be health-promoting phytochemicals. Anticarcinogenic, antibacterial, antiviral properties have been reported. A greenhouse, bag trial with virus-free plantlets of BP1 and SB cultivars was conducted using three water and nutrient levels and favourable root zone temperature(100% without heat, 100% heated, 50% heated, 25% heated) all grown in coco peat. Cultivar SB showed nearly two-fold yield compared to the control BP1. Methanol extracts of the tubers were assessed for their total polyphenolic, flavanol, and flavonol contents as well as 1-diphenyl-2-picrylhydrazyl (DPPH) scavenging ability, ferric reducing antioxidant power (FRAP), Trolox equivalence antioxidant capacity (TEAC),anthocyanin and L-ascorbic acid assays.The aqueous extract of the SB tubers was found to contain higher level of total polyphenols (320 mg GAE/g), and flavonol (85 mg QE/g) than the extract of the BP1 tubers with values of173 mg GAE/g (total polyphenol), and67 mg QE/g (flavonol). Similarly, the methanol extract of the tuber skins also exhibited higher DPPH (818,86 IC50mg/mL), FRAP (18,19μmol AAE/g), and TEAC (911,12μmol TE/g)than the extract of the BP1with DPPH (595,99 IC50mg/mL), FRAP (10,86 μmol AAE/g) and TEAC (435,44 μmol TE/g). The present study provides useful information for farmers and health professionals in respect to increased yield and health-promoting benefits of an underutilized potato variety.