Developing stress tolerant plants through in vitro selection—An overview of the recent progress

Enhancing in vitro regeneration via somatic embryogenesis and Fusarium wilt resistance of Egyptian cucumber (Cucumis sativus L.) cultivars

BACKGROUND

Somatic embryogenesis offers a reliable method for cucumber (Cucumis sativus L.) regeneration and genetic enhancement against Fusarium wilt. This study aimed to establish a tailored somatic embryogenesis system for Egyptian cultivars, fostering genetic improvements and Fusarium wilt-resistance lines.

RESULTS

Employing the Optimal Arbitrary Design (OAD) approach, we optimized the induction medium, initiating prolific embryogenic calli (53.3 %) at 1 mg/L 2,4-D. The cotyledonary leaf (CL) was the preferred explant, showing 60 % embryogenic callus development. Bieth Alpha exhibited higher responsiveness, generating ∼ 18 somatic embryos per explant compared to Prince's ∼ 10. Somatic embryogenesis system validation used quantitative RT-PCR, showing Cucumis sativus splicing factor 3B subunit (CUS1) and an embryogenesis marker gene expression exclusively within embryogenic calli and mainly during embryogenesis initiation. Evaluating fungal toxin filtrate concentrations for selecting embryogenic calli, the S2 selection (25 % filtrate, four subculture cycles) was chosen for somatic embryo development. To gauge the ramifications of selection at the genetic stratum, an in-depth analysis was executed. A cluster analysis grounded in ISSR banding patterns revealed a distinct separation between in vivo-cultivated plants of the two cultivars and regenerated plants devoid of pathogen filtrate treatment or those regenerated post-filtrate treatment. This segregation distinctly underscores the discernible genetic impact of the selection process.

CONCLUSIONS

The highest embryogenic capacity (53.3%) was achieved in this study by optimizing the induction stage, which demonstrated the optimal concentrations of BA and 2,4-D for induced proembryonic masses. Moreover, consistent gene expression throughout both stages of embryogenesis suggests that our system unequivocally follows the somatic embryogenesis pathway.

α-Tocopherol application as a countermeasure to UV-B stress in bread wheat (Triticum aestivum L.)

The source of energy for all photoautotrophic organisms is light, which is absorbed by photosynthetic processes and used to transform carbon dioxide and H2O into organic molecules. The majority of UV-B light (280 to 320 nm) is absorbed by stratospheric ozone layer, although some of it does reach at the Earth's surface. Because of the sedentary lifestyle of plants, this form of abiotic stress is unavoidable and can induce growth and even cell death. Ten-day-old calli generated from mature Kirik wheat embryos were subjected to UV-B radiation for 0, 2, 4, and 6 h to examine the function of exogenous α-tocopherol, a lipophilic antioxidant, in wheat tolerance to UV-B radiation stress. The calli were then moved to a callus medium containing α-tocopherol (0, 50, and 100 mg/l) and cultivated there for 20 days after being subjected to UV-B stress. For plant regeneration, embryogenic calli were put on a medium for plant regeneration after 30 days. The findings of this investigation demonstrated that an increase in UV-B exposure period resulted in a substantial drop in the relative growth rate of callus, the rate of embryogenic callus, the rate of responding embryogenic callus, and the number of plants in each explant. On the other hand, with the application of α-tocopherol, all these parameters improved, and the best result was observed in the application of 100 mg/l of α-tocopherol in terms of plant regeneration under UV-B stress.

Salt and drought stress-mitigating approaches in sugar beet (Beta vulgaris L.) to improve its performance and yield

MAIN CONCLUSION

Although sugar beet is a salt- and drought-tolerant crop, high salinity, and water deprivation significantly reduce its yield and growth. Several reports have demonstrated stress tolerance enhancement through stress-mitigating strategies including the exogenous application of osmolytes or metabolites, nanoparticles, seed treatments, breeding salt/drought-tolerant varieties. These approaches would assist in achieving sustainable yields despite global climatic changes. Sugar beet (Beta vulgaris L.) is an economically vital crop for ~ 30% of world sugar production. They also provide essential raw materials for bioethanol, animal fodder, pulp, pectin, and functional food-related industries. Due to fewer irrigation water requirements and shorter regeneration time than sugarcane, beet cultivation is spreading to subtropical climates from temperate climates. However, beet varieties from different geographical locations display different stress tolerance levels. Although sugar beet can endure moderate exposure to various abiotic stresses, including high salinity and drought, prolonged exposure to salt and drought stress causes a significant decrease in crop yield and production. Hence, plant biologists and agronomists have devised several strategies to mitigate the stress-induced damage to sugar beet cultivation. Recently, several studies substantiated that the exogenous application of osmolytes or metabolite substances can help plants overcome injuries induced by salt or drought stress. Furthermore, these compounds likely elicit different physio-biochemical impacts, including improving nutrient/ionic homeostasis, photosynthetic efficiency, strengthening defense response, and water status improvement under various abiotic stress conditions. In the current review, we compiled different stress-mitigating agricultural strategies, prospects, and future experiments that can secure sustainable yields for sugar beets despite high saline or drought conditions.

In vitro and in vivo screening for the identification of salt-tolerant sugarcane (Saccharum officinarum L.) clones: molecular, biochemical, and physiological responses to salt stress

Sugarcane is a glycophyte whose growth and yield can be negatively affected by salt stress. As the arable lands with potential saline soils expand annually, the increase of salt-tolerance in sugarcane cultivars is highly desired. We, herein, employed in vitro and in vivo conditions in order to screen sugarcane plants for salt tolerance at the cellular and at the whole plant levels. Calli of sugarcane cv. Khon Kaen 3 (KK3) were selected after culturing in selective media containing various NaCl concentrations, and regenerated plants were then reselected after culturing in selective media containing higher NaCl concentrations. The surviving plants were finally selected after an exposure to 254 mM NaCl under greenhouse conditions. A total of 11 sugarcane plants survived the selection process. Four plants that exhibited tolerance to the four different salt concentrations applied during the aforementioned screening process were then selected for the undertaking of further molecular, biochemical, and physiological studies. The construction of a dendrogram has revealed that the most salt-tolerant plant was characterized by the lowest genetic similarity to the original cultivar. The relative expression levels of six genes (i.e., SoDREB, SoNHX1, SoSOS1, SoHKT, SoBADH, and SoMIPS) were found to be significantly higher in the salt-tolerance clones than those measured in the original plant. The measured proline levels, the glycine betaine content, the relative water content, the SPAD unit, the contents of chlorophyll a and b, as well as the K⁺/Na⁺ ratios of the salt-tolerant clones were also found to be significantly higher than those of the original plant.When the salt-tolerant clones were grown in a low saline soil, they exhibited a higher Brix percentage than that of the original cultivar.

Breeding and Genomic Approaches towards Development of Fusarium Wilt Resistance in Chickpea

Chickpea is an important leguminous crop with potential to provide dietary proteins to both humans and animals. It also ameliorates soil nitrogen through biological nitrogen fixation. The crop is affected by an array of biotic and abiotic factors. Among different biotic stresses, a major fungal disease called Fusarium wilt, caused by Fusarium oxysporum f. sp. ciceris (FOC), is responsible for low productivity in chickpea. To date, eight pathogenic races of FOC (race 0, 1A, and 1B/C, 2-6) have been reported worldwide. The development of resistant cultivars using different conventional breeding methods is very time consuming and depends upon the environment. Modern technologies can improve conventional methods to solve these major constraints. Understanding the molecular response of chickpea to Fusarium wilt can help to provide effective management strategies. The identification of molecular markers closely linked to genes/QTLs has provided great potential for chickpea improvement programs. Moreover, omics approaches, including transcriptomics, metabolomics, and proteomics give scientists a vast viewpoint of functional genomics. In this review, we will discuss the integration of all available strategies and provide comprehensive knowledge about chickpea plant defense against Fusarium wilt.

Polyethylene Glycol and Sorbitol-Mediated In Vitro Screening for Drought Stress as an Efficient and Rapid Tool to Reach the Tolerant Cucumis melo L. Genotypes

An efficient method to instantly assess drought-tolerant plants after germination is using osmoregulation in tissue culture media. In this study, the responses of three Iranian melon genotypes to sorbitol (0.1, 0.2, and 0.4 M) or polyethylene glycol (PEG) (0.009, 0.012, and 0.015 M) were evaluated as drought stress simulators in MS medium. 'Girke' (GIR), 'Ghobadloo' (GHO), and 'Toghermezi' (TOG) were the genotypes. GIR is reputed as a drought-tolerant genotype in Iran. The PEG or sorbitol decreased the coleoptile length, fresh weight, and photosynthetic pigments content while enhancing proline and malondialdehyde (MDA) contents. Protein content and antioxidant enzyme activity were utterly dependent on genotype, osmotic regulators, and their concentration. Coleoptile length, root and shoot fresh weight, root dry weight, proline and MDA content, and guaiacol peroxidase (GPX) activity can be used as indicators for in vitro screening of Cucumis melo L. genotypes. The results showed that sorbitol mimics drought stress better than PEG. Overall, our findings suggest that in vitro screening could be an accurate, rapid, and reliable methodology for evaluating and identifying drought-tolerant genotypes.

Medicago sativa and M. tunetana reveal contrasting physiological and metabolic responses to drought

Alfalfa production is frequently constrained by drought, indicating the importance of assessing species biodiversity in endemic close relatives to enhance forage production under future global change conditions. In the present study, plants of two ecotypes of M. tunetana, native to Tunisia, and four commercial cultivars of M. sativa were subjected to two water regimes (control vs drought [15% field capacity]). Physiological, isotopic and metabolic analyses were used to characterize leaf and nodule profiles of the plants. Biomass, gas exchange and the maximum carboxylation rate (Vc_max) indicated significant decreases in photosynthetic capacity under drought in M. sativa cultivars. However, M. tunetana ecotypes maintained photosynthetic performance and aboveground biomass under drought conditions. Furthermore, nitrogen isotope composition (δ¹⁵N) in nodules and leaves was significantly decreased, which reveals a reduction in the N₂ fixing activity of nodules under drought conditions that was not translated into lower leaf N content but was probably due to lower N demand. Analyses of starch, soluble sugar, and amino acid content in leaves and nodules have clearly proven the ability of Medicago spp. cultivars to increase the accumulation of osmo-protectors under drought. This study demonstrated the genetic variability of the strategy adopted among the studied cultivars in response to drought. In this sense, M. tunetana, and in part the M. sativa cultivar adapted to Mediterranean conditions, seem capable of maintaining adequate biomass, photosynthesis and biological N₂ fixation in comparison to the other M. sativa cultivars.

Plants in vitro propagation with its applications in food, pharmaceuticals and cosmetic industries; current scenario and future approaches

Plant tissue culture technique employed for the identification and isolation of bioactive phytocompounds has numerous industrial applications. It provides potential benefits for different industries which include food, pharmaceutical and cosmetics. Various agronomic crops i.e., cereals, fruits, vegetables, ornamental plants and forest trees are currently being used for in vitro propagation. Plant tissue culture coupled with biotechnological approaches leads towards sustainable agricultural development providing solutions to major food security issues. Plants are the rich source of phytochemicals with medicinal properties rendering them useful for the industrial production of pharmaceuticals and nutraceuticals. Furthermore, there are numerous plant compounds with application in the cosmetics industry. In addition to having moisturizing, anti-ageing, anti-wrinkle effects; plant-derived compounds also possess pharmacological properties such as antiviral, antimicrobial, antifungal, anticancer, antioxidant, anti-inflammatory, and anti-allergy characteristics. The in vitro propagation of industrially significant flora is gaining attention because of its several advantages over conventional plant propagation methods. One of the major advantages of this technique is the quick availability of food throughout the year, irrespective of the growing season, thus opening new opportunities to the producers and farmers. The sterile or endangered flora can also be conserved by plant micro propagation methods. Hence, plant tissue culture is an extremely efficient and cost-effective technique for biosynthetic studies and bio-production, biotransformation, or bioconversion of plant-derived compounds. However, there are certain limitations of in-vitro plant regeneration system including difficulties with continuous operation, product removal, and aseptic conditions. For sustainable industrial applications of in-vitro regenerated plants on a large scale, these constraints need to be addressed in future studies.

Influence of toxic diesel fuel on Petunia grandiflora calli and after plant regeneration

The toxic effects of diesel fuel on whole plants have been reported before, but little is known about the toxic effect of diesel fuel on callus cultures. This knowledge is a pre-requisite for exploring the possibility of using a sub-lethal diesel concentration as an agent for in vitro cell line selection to obtain novel somaclonal variants resistant to diesel toxicity. These novel variants could be useful for the phytoremediation of diesel-contaminated soil. Here, a callus induction medium [Murashige and Skoog medium supplemented with 1.8 µM of naphthlene-1-acetic acid (NAA) and 6.6 µM of 6-benzyladenine (BA)] was found to induce 85% of Petunia grandiflora leaf explants to form light green calli. Since it was not possible to include diesel in aseptic culture, the P. grandiflora calli were exposed to diesel under non-aseptic conditions. It was found that the calli did not exhibit any sign of necrosis immediately after up to 9 min of diesel exposure. The diesel-treated calli were subsequently subcultured successfully on the callus induction medium using the proliferating, non-necrotic cells. Transverse sections of the control and diesel-treated calli after 2 weeks of culture revealed that the control calli exhibited more small meristematic cells while diesel-treated calli exhibited larger, empty-looking parenchyma cells. Moreover, it was possible to induce, though at a low frequency (< 15%), shoot formation in the control calli and those derived from the diesel treatment on the Murashige and Skoog medium supplemented with 1.1 µM of indole-3-acetic acid (IAA) and 13.3 µM of BA. Under glasshouse conditions, the shoots regenerated from the calli derived from the diesel treatment exhibited higher biomass than those from the control calli and P. grandiflora seedlings when grown in a potting mix spiked with 0%, 2% and 7% diesel. Taken together, these results suggest that up to 9 min of diesel exposure of P. grandiflora calli was sub-lethal.

Microbial Diversity and Adaptation under Salt-Affected Soils: A Review

The salinization of soil is responsible for the reduction in the growth and development of plants. As the global population increases day by day, there is a decrease in the cultivation of farmland due to the salinization of soil, which threatens food security. Salt-affected soils occur all over the world, especially in arid and semi-arid regions. The total area of global salt-affected soil is 1 billion ha, and in India, an area of nearly 6.74 million ha−1 is salt-stressed, out of which 2.95 million ha−1 are saline soil (including coastal) and 3.78 million ha−1 are alkali soil. The rectification and management of salt-stressed soils require specific approaches for sustainable crop production. Remediating salt-affected soil by chemical, physical and biological methods with available resources is recommended for agricultural purposes. Bioremediation is an eco-friendly approach compared to chemical and physical methods. The role of microorganisms has been documented by many workers for the bioremediation of such problematic soils. Halophilic Bacteria, Arbuscular mycorrhizal fungi, Cyanobacteria, plant growth-promoting rhizobacteria and microbial inoculation have been found to be effective for plant growth promotion under salt-stress conditions. The microbial mediated approaches can be adopted for the mitigation of salt-affected soil and help increase crop productivity. A microbial product consisting of beneficial halophiles maintains and enhances the soil health and the yield of the crop in salt-affected soil. This review will focus on the remediation of salt-affected soil by using microorganisms and their mechanisms in the soil and interaction with the plants.

Functional analysis of mitogen-activated protein kinases (MAPKs) in potato under biotic and abiotic stress

Biotic and abiotic stresses are the main constrain of potato (Solanum tuberosum L.) production all over the world. To overcome these hurdles, many techniques and mechanisms have been used for increasing food demand for increasing population. One of such mechanism is mitogen-activated protein kinase (MAPK) cascade, which is significance regulators of MAPK pathway under various biotic and abiotic stress conditions in plants. However, the acute role in potato for various biotic and abiotic resistance is not fully understood. In eukaryotes including plants, MAPK transfer information from sensors to responses. In potato, biotic and abiotic stresses, as well as a range of developmental responses including differentiation, proliferation, and cell death in plants, MAPK plays an essential role in transduction of diverse extracellular stimuli. Different biotic and abiotic stress stimuli such as pathogen (bacteria, virus, and fungi, etc.) infections, drought, high and low temperatures, high salinity, and high or low osmolarity are induced by several MAPK cascade and MAPK gene families in potato crop. The MAPK cascade is synchronized by numerous mechanisms, including not only transcriptional regulation but also through posttranscriptional regulation such as protein-protein interactions. In this review, we will discuss the recent detailed functional analysis of certain specific MAPK gene families which are involved in resistance to various biotic and abiotic stresses in potato. This study will also provide new insights into functional analysis of various MAPK gene families in biotic and abiotic stress response as well as its possible mechanism.

Tetraploidy Confers Superior in vitro Water-Stress Tolerance to the Fig Tree (Ficus carica) by Reinforcing Hormonal, Physiological, and Biochemical Defensive Systems

The fig tree is a well-adapted and promising fruit tree for sustainable production in arid and semi-arid areas worldwide. Recently, Iran's dryland fig orchards have been severely damaged due to prolonged severe and consecutive drought periods. As emphasized in many studies, ploidy manipulated plants have a significantly enhanced drought tolerance. In the current study, we compared the induced autotetraploid explants of two fig cultivars ('Sabz' and 'Torsh') with their diploid control plants for their water stress tolerance under in vitro conditions using different polyethylene glycol (PEG) concentrations (0, 5, 10, 15, 20, and 25%). After 14 days of implementing water stress treatments, the results revealed that both tetraploid genotypes survived at 20% PEG treatments. Only 'Sabz' tetraploid explants survived at 25% PEG treatment, while both diploid control genotypes could tolerate water stress intensity only until 15% PEG treatment. The results also demonstrated that the tetraploid explants significantly had a higher growth rate, more leaf numbers, and greater fresh and dry weights than their diploid control plants. Under 15% PEG treatment, both tetraploid genotypes could maintain their relative water content (RWC) at a low-risk level (80-85%), while the RWC of both diploid genotypes drastically declined to 55-62%. The ion leakage percentage also was significantly lower in tetraploid explants at 15% PEG treatment. According to the results, these superiorities could be attributed to higher levels of stress response hormones including abscisic acid, salicylic acid, and jasmonic acid at different PEG treatments, the robust osmotic adjustment by significantly increased total soluble sugar (TSS), proline, and glycine betaine contents, and augmented enzymatic defense system including significantly increased superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) activities in tetraploid genotypes, compared to their diploid control genotypes. Consequently, the current study results demonstrated that the 'Sabz' tetraploid genotype had a significantly higher water stress tolerance than other tested genotypes.

Embryo Culture, In Vitro Propagation, and Molecular Identification for Advanced Olive Breeding Programs

The high biodiversity of the olive tree is an important opportunity to develop sustainable plans to control Xylella fastidiosa (Xf) through breeding programs. Olive tree breeding activities have been limited due to various features of this species including the long time required for seed germination caused by the inhibition effect of the woody endocarp, the seed integument, and the endosperm. Starting from F1 seeds by cross-breeding, the embryo culture was compared with traditional seed germination, evaluating the effectiveness of in vitro multiplication of the plantlets for large-scale production. The isolated embryos were established on a new medium based on Rugini ‘84 macroelements, Murashige & Skoog ‘62 microelements, with Nitsch J. P. & Nitsch C. ‘69 vitamine and subcultured on Leva MSM modified. The results obtained confirmed that in vitro culture of olive embryos is a valid tool for increasing the percentage and speed of germination, helping to reduce the time of the olive breeding programs, offering the possibility to effectively propagate plantlets for further experiments.

Callus induction and regeneration in sugarcane under drought stress

Tissue culture methods are useful in assessing the tolerance of various stresses due to the ease of controlling stress under in vitro conditions. This study aimed to investigate the response of sugarcane genotyps to drought stress using calli as a model system. For inducing sugarcane callus, the medium of Murashige and Skoog (MS) was used with different mannitol concentrations (100, 200, and 300 mM) to measure their effects on callus frequency, the day of callus initiation, embryogenic potential, relative growth rate (RGR), water and proline contents, K+ and Na+ contents, as well as the formation of shoot and roots for three sugarcane genotypes (e.g., GT 54-9, G 84-47, and pH 8013). The RAPD-PCR analysis was carried out using five oligonucleotide primers to identify the genetic variation among sugarcane genotypes. The results indicated that the degree of callus proliferation varied from 70 - 86%. The highest value of callus proliferation, PGR, shoot formation was recorded for the genotype GT 54-9 compared to the other two genotypes (G 84-47 and pH 8013). Calli treated with 100 mM mannitol showed the highest RGR, proline and waer contents for the genotype GT 54-9, while, those treated with 300 mM recorded the lowest values of these parameters for the genotype pH 8013. The genotype G 84-47 collected highest Na+ content, while the genotype pH 8013 collected highest K+ content. The results of this study recommend preference for GT 54-9 genotype, which is considered the most promising genotype, showing more tolerance to drought stress based on all studied traits.

In vitro response of vanilla (Vanilla planifolia Jacks. ex Andrews) to PEG-induced osmotic stress

Drought-induced water stress affects the productivity of the Vanilla planifolia Jacks. ex Andrews crop. In vitro culture technique is an effective tool for the study of water stress tolerance mechanisms. This study aimed to evaluate the morphological, physiological and biochemical response of V. planifolia under in vitro water stress conditions induced with polyethylene glycol (PEG). In vitro regenerated shoots of 2 cm in length were subjected to different concentrations of PEG 6000 (0, 1, 2 and 3% w/v) using Murashige and Skoog semi-solid culture medium. At 60 days of culture, different growth variables, dry matter (DM) content, chlorophyll (Chl), soluble proteins (SP), proline (Pro), glycine betaine (GB), stomatal index (SI) and open stomata (%) were evaluated. Results showed a reduction in growth, Chl content, SP, SI and open stomata (%) with increasing PEG concentration, whereas DM, Pro and GB contents rose with increasing PEG concentration. In conclusion, PEG-induced osmotic stress allowed describing physiological and biochemical mechanisms of response to water stress. Furthermore, the determination of compatible Pro and GB osmolytes can be used as biochemical markers in future breeding programs for the early selection of water stress tolerant genotypes.

Proteins, Small Peptides and Other Signaling Molecules Identified as Inconspicuous but Possibly Important Players in Microspores Reprogramming Toward Embryogenesis

In this review, we describe and integrate the latest knowledge on the signaling role of proteins and peptides in the stress-induced microspore embryogenesis (ME) in some crop plants with agricultural importance (i.e., oilseed rape, tobacco, barley, wheat, rice, triticale, rye). Based on the results received from the most advanced omix analyses, we have selected some inconspicuous but possibly important players in microspores reprogramming toward embryogenic development. We provide an overview of the roles and downstream effect of stress-related proteins (e.g., β-1,3-glucanases, chitinases) and small signaling peptides, especially cysteine—(e.g., glutathione, γ-thionins, rapid alkalinization factor, lipid transfer, phytosulfokine) and glycine-rich peptides and other proteins (e.g., fasciclin-like arabinogalactan protein) on acclimation ability of microspores and the cell wall reconstruction in a context of ME induction and haploids/doubled haploids (DHs) production. Application of these molecules, stimulating the induction and proper development of embryo-like structures and green plant regeneration, brings significant improvement of the effectiveness of DHs procedures and could result in its wider incorporation on a commercial scale. Recent advances in the design and construction of synthetic peptides–mainly cysteine-rich peptides and their derivatives–have accelerated the development of new DNA-free genome-editing techniques. These new systems are evolving incredibly fast and soon will find application in many areas of plant science and breeding.

Physiological Response of Maize Plants (Zea mays L.) to the Use of the Potassium Quercetin Derivative

Plant production technologies based solely on the improvement of plants themselves face obstacles resulting from the natural limitations of the biological potential of varieties. Therefore, new substances are sought that positively influence the growth and development of plants and increase resistance to various biotic and abiotic stresses, which also translates into an increase in obtained yields. The exogenous application of various phytoprotectants shows great promise in terms of cost effectiveness compared to traditional breeding methods or transgenic approaches in relation to increasing plant tolerance to abiotic stresses. Quercetin is a strong antioxidant among phenolic compounds, and it plays a physiological and biochemical role in plants. As such, the aim of this research was to assess the effect of an aqueous solution of a quercetin derivative with potassium, applied in various concentrations (0.5%, 1.0%, 3.0% and 5.0%), on the efficiency of the photosynthetic apparatus and biochemical properties of maize. Among the tested variants, compared to the control, the most stimulating effect on the course of physiological processes (PN, gs, ci, CCI, Fv/Fm, Fv/F0, PI) in maize leaves was found in 3.0 and 5.0% aqueous solutions of the quercetin derivative. The highest total antioxidant capacity and total content of polyphenolic compounds were found for plants sprayed with 5.0% quercetin derivative solution; therefore, in this study, the optimal concentration could not be clearly selected.

Comparison of Four Systems to Test the Tolerance of ‘Fortune’ Mandarin Tissue Cultured Plants to Alternaria alternata

Alternaria brown spot is a severe disease that affects leaves and fruits on susceptible mandarin and mandarin-like cultivars, and is produced by Alternaria alternata. Consequently, there is an urge to obtain new cultivars resistant to A. alternata, and mutation breeding together with tissue culture can help shorten the process. However, a protocol for the in vitro selection of resistant citrus genotypes is lacking. In this study, four methods to evaluate the sensitivity to Alternaria of mandarin ‘Fortune’ explants in in vitro culture were tested. The four tested systems consisted of: (1) the addition of the mycotoxin, produced by A. alternata in ‘Fortune’, to the propagation culture media, (2) the addition of the A. alternata culture filtrate to the propagation culture media, (3) the application of the mycotoxin to the intact shoot leaves, and (4) the application of the mycotoxin to the previously excised and wounded leaves. After analyzing the results, only the addition of the A. alternata culture filtrate to the culture media and the application of the mycotoxin to the wounded leaves produced symptoms of infection. However, the addition of the fungus culture filtrate to the culture media produced results, which might indicate that, in addition to the mycotoxin, many other unknown elements that can affect the plant growth and behavior could be found in the fungus culture filtrate. Therefore, the application of the toxin to the excised and wounded leaves seems to be the most reliable method to analyze sensitivity to Alternaria of ‘Fortune’ explants cultured in vitro.

Growth and Biochemical Responses of Potato Cultivars under In Vitro Lithium Chloride and Mannitol Simulated Salinity and Drought Stress

Globally, drought and salinity stress critically constrain potato (Solanum tuberosum L.) production. Considering the impact of these stresses on crops and increasing food demand, insight into both tolerance and susceptibility is essential. The present study screens two potato cultivars, BARI-401 and Spunta, for their tolerance to simulated salinity and drought by in vitro LiCl and mannitol exposure. Plantlets treated with a range of LiCl (0, 10, 30, and 40 mM) and mannitol (0, 50, 100, 200, and 250 mM) concentrations were biochemically and physiologically characterized to assess their tolerance capacity. Shoot number, shoot length, root number, and root length were affected in both cultivars under higher LiCl and mannitol concentrations, even though Spunta was able to better maintain a higher shoot length under the 40 mM of LiCl and 250 mM of mannitol compared to BARI-401. The total phenol contents (TPC) in both cultivars were increased at the highest treatment concentration and the total flavonoids content (TFC) was decreased in BARI-401 as compared to Spunta. Higher free radical scavenging capacity (FRSC, low IC50 value) was recorded in Spunta as compared to BARI-401 with increasing treatment concentrations, which supports the high antioxidant capacity of Spunta. An inverse correlation between polyphenol oxidase (PPO) and TPC was noted in both cultivars. Peroxidase dismutase (POD) activity was increased significantly in both cultivars for all treatments, but activity was highest overall in Spunta. These physiological and biochemical analyses of both cultivars suggest that cultivar Spunta is more tolerant to salinity and drought stress. Further open-field experiments are required to confirm these results.

Cell Suspension Culture and In Vitro Screening for Drought Tolerance in Soybean Using Poly-Ethylene Glycol

Soybean (Glycine max (L) Merrill) is used in India mostly as a substantial fund of protein and oil, which makes the crop significantly important. Somaclonal variation has been researched as a base of additional variability for drought in soybean. In the present experiment calli/cell clumps/embryoids rose from immature and mature embryonic axis and cotyledons explants were exposed to different concentrations of polyethylene glycol (PEG6000). A discontinuous method proved to be superior as it permitted the calli/embryoids/cell clumps to regain their regeneration competence. A total of 64 (12.21%) plantlets of genotype JS335 and 78 (13.13%) of genotype JS93-05 were regenerated after four consequent subcultures on the selection medium with an effective lethal concentration of 20% PEG6000, and proliferated calli/embryoids/cell clumps were further subcultured on Murashige and Skoog regeneration medium supplemented with 0.5 mgL^-1 each of α-napthalene acetic acid (NAA), 6-benzyladenine (BA) and Kinetin (Kn), 20.0 gL^-1 sucrose and 7.5 gL^-1 agar. Putative drought-tolerant plantlets were acquired from genotype JS93-05 (38) in more numbers compared to genotype JS335 (26). Random decamer primers confirmed the presence of variability between mother plants and regenerated plants from both the genotypes. Since these plantlets recovered from tolerant calli/embryoids/cell clumps selected from the medium supplemented with PEG6000, the possibility exists that these plants may prove to be tolerant against drought stress.

Metabolomic and Biochemical Analysis of Two Potato (Solanum tuberosum L.) Cultivars Exposed to In Vitro Osmotic and Salt Stresses

Globally, many crop production areas are threatened by drought and salinity. Potato (Solanum tuberosum L.) is susceptible to these challenging environmental conditions. In this study, an in vitro approach was employed to compare the tolerance of potato cultivars ‘BARI-401’ (red skin) and ‘Spunta’ (yellow skin). To simulate ionic and osmotic stress, MS media was supplemented with lithium chloride (LiCl 20 mM) and mannitol (150 mM). GC-MS and spectrophotometry techniques were used to determine metabolite accumulation. Other biochemical properties, such as total phenols concentration (TPC), total flavonoids concentration (TFC), antioxidant capacity (DPPH free radical scavenging capacity), polyphenol oxidase (PPO), and peroxidase (POD) activities, were also measured. The two cultivars respond differently to ionic and osmotic stress treatments, with Spunta accumulating more defensive metabolites in response, indicating a higher level of tolerance. While further investigation of the physiological and biochemical responses of these varieties to drought and salinity is required, the approach taken in this paper provides useful information prior to open field evaluation.

Biochemical and Genetic Responses of Tea (Camellia sinensis (L.) Kuntze) Microplants under Mannitol-Induced Osmotic Stress In Vitro

Osmotic stress is a major factor reducing the growth and yield of many horticultural crops worldwide. To reveal reliable markers of tolerant genotypes, we need a comprehensive understanding of the responsive mechanisms in crops. In vitro stress induction can be an efficient tool to study the mechanisms of responses in plants to help gain a better understanding of the physiological and genetic responses of plant tissues against each stress factor. In the present study, the osmotic stress was induced by addition of mannitol into the culture media to reveal biochemical and genetic responses of tea microplants. The contents of proline, threonine, epigallocatechin, and epigallocatechin gallate were increased in leaves during mannitol treatment. The expression level of several genes, namely DHN2, LOX1, LOX6, BAM, SUS1, TPS11, RS1, RS2, and SnRK1.3, was elevated by 2–10 times under mannitol-induced osmotic stress, while the expression of many other stress-related genes was not changed significantly. Surprisingly, down-regulation of the following genes, viz. bHLH12, bHLH7, bHLH21, bHLH43, CBF1, WRKY2, SWEET1, SWEET2, SWEET3, INV5, and LOX7, was observed. During this study, two major groups of highly correlated genes were observed. The first group included seven genes, namely CBF1, DHN3, HXK2,SnRK1.1, SPS, SWEET3, and SWEET1. The second group comprised eight genes, viz. DHN2, SnRK1.3, HXK3, RS1, RS2,LOX6, SUS4, and BAM5. A high level of correlation indicates the high strength connection of the genes which can be co-expressed or can be linked to the joint regulons. The present study demonstrates that tea plants develop several adaptations to cope under osmotic stress in vitro; however, some important stress-related genes were silent or downregulated in microplants.

Selection of somaclonal variants of maracuyá (passiflora Edulis var Flavicarpa. Deneger) tolerants to water deficit

Climate change will have an impact on the Colombian agricultural sector, by 2050 increases in temperature and distribution of erratic rainfall are expected. Passion fruit cultivation does not tolerate water deficit, it reduces flower induction, generates fruit drop and defoliation. To tackle this problem, somaclonal variants (VS) of passion fruit were selected in-vitro, seeking tolerance to water deficit. Four phases were developed: I) callogenesis, II) direct and indirect organogenesis, II) Induction and evaluation of the water deficit with Polyethylene glycol 6000 (PEG 6000) and IV) in vitro selection of VS by morphometric measurements, chlorophyll and total sugars contents. Differences in callogenesis were found with different concentrations of 2,4-D, the concentration of 2 mg • L-1 presented better results producing calluses in less time and in greater quantity (8 days, 90% of the leaf area). In indirect and direct organogenesis the medium MS + ANA + BAP (0.3: 0.6), showed significant statistical differences with respect to other means, for the variables root length (15.14 cm), stem (16.72 cm) and leaves ( 14.51 cm) and root thickness (0.76 cm) stem (1.25) and leaf width (6.75). The influence of PEG 6000 showed significant differences, the treatment with 30 g • L-1 showed the smallest leaf width, the greatest width was found in 25 g • L-1. Statistical differences were found in chlorophyll levels and total sugar contents, the highest contents were recorded in the VS 25VS1, showing the possibility of obtaining seedlings tolerant to the water deficit of passion fruit by inducing somaclonal variation.

From cells highly tolerant to Zn and Pb to fully fertile plants - Selection of tolerant lines with in vitro culture

Viola arvensis cells were selected after treatment with Zn or Pb and regenerated into plants likely to have higher tolerance levels than the initial plant. The surviving cells in the suspension treated with 2000 μM of Zn, 2000 μM of Pb or 0 μM for 72 h were maintained on a solidified half-strength MS medium supplemented with 0.5 mg L^-1 TDZ to induce divisions and organogenesis. The adventitious shoots obtained were rooted on a half-strength MS medium with 1 mg L^-1 IBA. Regenerants derived from the Zn- and Pb-treated cells were vigorous and fully fertile. The in vitro conditions and metal impact generated a low genome alteration and overall low genetic diversity of regenerants compared to the initial plant and plants from the natural population. The cells of regenerants obtained after Pb treatment represented an approximately 12% higher tolerance level to Pb than the cells of the initial plant. This is the first report of plant regeneration from highly tolerant cells selected by heavy metal treatment. Regenerants successfully obtained in vitro could be considered as a source material for the recultivation of areas polluted with heavy metals.

Cyclic tetrapeptides from the marine strain Streptomyces sp. PNM-161a with activity against rice and yam phytopathogens

Two cyclotetrapeptides, henceforth named Provipeptides A (1) and B (2), along with five known diketopiperazines (3-7) were isolated from the liquid culture of marine Streptomyces sp. 161a recovered from a sample of sea grass Bryopsis sp. The structures of cyclotetrapeptides and diketopiperazines (DKPs) were established by 1D and 2D NMR data, MS, and by comparison with literature data. The absolute stereochemistry of compounds cyclo-(L-Pro-L-Leu-D-Pro-L-Phe) 1 and cyclo-(-Pro-Ile-Pro-Phe) 2 was established by the Marfey's method. Compound 1 showed antibacterial activity against rice phytopathogenic strains Burkholderia glumae (MIC = 1.1 mM) and Burkholderia gladioli (MIC = 0.068 mM), compound 2 was active only against B. glumae (MIC = 1.1 mM), and DKP cyclo-[L-Pro-L-Leu] 5 showed to be active against B. gladioli (MIC = 0.3 mM) and B. glumae (MIC = 2.4 mM). Compounds 1 and 2 showed 65% and 50% inhibition of Colletotrichum gloeosporioides (yam pathogen) conidia germination, respectively at a concentration of 1.1 mM.

Biostimulants Application in Horticultural Crops under Abiotic Stress Conditions

Abiotic stresses strongly affect plant growth, development, and quality of production; final crop yield can be really compromised if stress occurs in plants’ most sensitive phenological phases. Additionally, the increase of crop stress tolerance through genetic improvements requires long breeding programmes and different cultivation environments for crop performance validation. Biostimulants have been proposed as agronomic tools to counteract abiotic stress. Indeed, these products containing bioactive molecules have a beneficial effect on plants and improve their capability to face adverse environmental conditions, acting on primary or secondary metabolism. Many companies are investing in new biostimulant products development and in the identification of the most effective bioactive molecules contained in different kinds of extracts, able to elicit specific plant responses against abiotic stresses. Most of these compounds are unknown and their characterization in term of composition is almost impossible; therefore, they could be classified on the basis of their role in plants. Biostimulants have been generally applied to high-value crops like fruits and vegetables; thus, in this review, we examine and summarise literature on their use on vegetable crops, focusing on their application to counteract the most common environmental stresses.

Na+ and Cl- induce differential physiological, biochemical responses and metabolite modulations in vitro in contrasting salt-tolerant soybean genotypes

Chloride and sodium constitute as the major ions in most saline soils, contributing to salt-induced damage in plants. Research on salt tolerance has mostly concentrated on the sodium toxicity; however, chloride toxicity also needs to be considered to understand the physiological, biochemical, and metabolite changes under individual and additive salts. In this study, we investigated the effect of individual Na⁺ and/or Cl^- ions (equimolar 100 mM NaCl, Na⁺ and Cl^- salts) using in vitro cultures of four soybean genotypes with contrasting salt tolerance. In general, all the treatments significantly induced antioxidant enzymes activities such as catalase, ascorbate peroxidase, glutathione reductase, guaiacol peroxidase, and superoxide dismutase and osmolytes including proline, glycine betaine, and total soluble sugar (TSS). Both individual (Na⁺, Cl^-) and additive (NaCl) stresses induced more pronounced activation of antioxidant enzyme machinery and osmolytes accumulation in the tolerant genotypes (MAUS-47 and Bragg). The sensitive genotypes (Gujosoya-2 and SL-295) showed higher accumulation of Na⁺ and Cl^-, while the tolerant genotypes were found to maintain a low Na⁺/K⁺ and high Ca²⁺ level in combination with enhanced antioxidant defense and osmotic adjustment. Gas chromatography-mass spectrometry (GC-MS)-based metabolomic profiling depicted the association of certain metabolites under individualistic and additive salt effects. The genotype-specific metabolic changes indicated probable involvement of azetidine, 2-furanmethanol, 1,4-dioxin, 3-fluorothiophene, decanoic acid and 2-propenoic acid methyl ester in salt-tolerance mechanism of soybean.

Uprising the antioxidant power of Argania spinosa L. callus through abiotic elicitation

This study was carried out in order to investigate the ability of tissues of Argania spinosa (L.) to undergo unlimited cell divisions by triggering their proliferative potential via callogenesis. Axenic cultures were efficiently established using axillary buds cultured on half-strength Murashige and Skoog (MS) medium after 20min of surface sterilization with sodium hypochlorite 6% (v/v). The highest callus rate was achieved with 1.0mgL^-1 of naphthaleneacetic acid (NAA) and 1.0mgL^-1 of 2,4-dichlorophenoxyacetic acid (2,4D) or similarly with 0.01mgL^-1 of 6-benzylaminopurine (BAP) and 1.0mgL^-1 of 2,4D at pH of 5.8, under dark conditions. The results of this study show also a significant increase in the callus's antioxidant power under abiotic pressure induced by NaCl. Catalase (CAT), peroxidase (PO), and superoxide dismutase (SOD) activities were significantly triggered, which protected the cells from the stimulated oxidative stress, under hydrogen peroxide (H₂O₂) significant release. This reaction favors subsequently the tissue recover process linked to the low abundance of polyphenol oxidase (PPO) activity and malondialdehyde (MDA) content. This work proves the efficiency of salt stress in boosting the argan cell's antioxidant status, which could be commercially applied in the field of cells regenerative therapy.

Study of gene expression and steviol glycosides accumulation in Stevia rebaudiana Bertoni under various mannitol concentrations

Stevia rebaudiana produces sweet steviol glycosides that are 300 times sweeter than sugar and have the beneficial effects on human health including anti-hyperglycaemic. Tissue culture is the best method with high efficacy to propagate stevia. Abiotic stress has an impact on steviol glycoside contents in stevia. Therefore, we investigated the effect of mannitol on the expression of four genes involved in the biosynthesis of stevia including UGT74G1, UGT76G1, kaurene oxidase and kaurene synthase genes and steviol glycosides accumulation in stevia under in vitro conditions. The highest expression of UGT76G1 gene occurred in the plants grown under 20 g/l mannitol. While for the kaurene synthase gene, the highest amount of gene expression was observed at 40 g/l mannitol. The results were different about kaurene oxidase gene. As the highest and lowest gene expression were seen in 50 and 30 g/l mannitol conditions respectively. There were the same results for UGT74G1 that means the most appropriate and also the most inopportune treatment for the gene expression were same as the condition for the kaurene oxidase gene. Compared with control, adding mannitol to media in all concentrations increases the expression of UGT76G1 gene. Estimation of steviol glycosides contents under different treatments of mannitol carried out by HPLC. According to the results, the highest amount of stevioside was produced under 20 g/l mannitol treatment. However, rebaudioside A was accumulated in its maximum amounts under 30 g/l mannitol. It can be concluded that adding mannitol to media in the certain concentration increases steviol glycoside contents in the stevia.

Reducing Water Availability Impacts the Development of the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis MUCL 41833 and Its Ability to Take Up and Transport Phosphorus Under in Vitro Conditions

Climate change scenarios predict a higher variability in rainfall and an increased risk of water deficits during summers for the coming decades. For this reason, arbuscular mycorrhizal fungi (AMF) and their mitigating effects on drought stress in plants are increasingly considered in crop management. However, the impact of a decrease in water availability on the development of AMF and their ability to take up and transport inorganic phosphorus (Pi) to their hosts remain poorly explored. Here, Medicago truncatula plantlets were grown in association with Rhizophagus irregularis MUCL 41833 in bi-compartmented Petri plates. The system consisted in associating the plant and AMF in a root compartment (RC), allowing only the hyphae to extend in a root-free hyphal compartment (HC). Water availability in the HC was then lowered by increasing the concentration of polyethylene glycol-8000 (PEG-8000) from 0 to 10, 25, and 50 g L-1 (corresponding to a slight decrease in water potential of -0.024, -0.025, -0.030, and -0.056 Mpa, respectively). Hyphal growth, spore production and germination were severely impaired at the lowest water availability. The dynamics of Pi uptake by the AMF was also impacted, although total Pi uptake evaluated after 24 h stayed unchanged. The percentage of metabolically active extraradical hyphae remained above 70%. Finally, at the lowest water availability, a higher P concentration was observed in the shoots of M. truncatula. At reduced water availability, the extraradical mycelium (ERM) development was impacted, potentially limiting its capacity to explore a higher volume of soil. Pi uptake was slowed down but not prevented. The sensitivity of R. irregularis MUCL 41833 to a, even small, decrease in water availability contrasted with several studies reporting tolerance of AMF to drought. This suggests a species or strain-dependent effect and support the necessity to compare the impact of water availability on morpho-anatomy, nutrient uptake and transport capacities of other, potentially more drought-tolerant (e.g., isolated from dry environments) AMF.

Identification of SNPs and Candidate Genes Associated With Salt Tolerance at the Seedling Stage in Cotton (Gossypium hirsutum L.)

Salt tolerance in cotton is highly imperative for improvement in the response to decreasing farmland and soil salinization. However, little is known about the genetic basis underlying salt tolerance in cotton, especially the seedling stage. In this study, we evaluated two salt-tolerance-related traits of a natural population comprising 713 upland cotton (Gossypium hirsutum L.) accessions worldwide at the seedling stage and performed a genome-wide association study (GWAS) to identify marker-trait associations under salt stress using the Illumina Infinium CottonSNP63K array. A total of 23 single nucleotide polymorphisms (SNPs) that represented seven genomic regions on chromosomes A01, A10, D02, D08, D09, D10, and D11 were significantly associated with the two salt-tolerance-related traits, relative survival rate (RSR) and salt tolerance level (STL). Of these, the two SNPs i46598Gh and i47388Gh on D09 were simultaneously associated with the two traits. Based on all loci, we screened 280 possible candidate genes showing different expression levels under salt stress. Most of these genes were involved in transcription factors, transporters and enzymes and were previously reported as being involved in plant salt tolerance, such as NAC, MYB, NXH, WD40, CDPK, LEA, and CIPK. We further validated six putative candidate genes by qRT-PCR and found a differential expression level between salt-tolerant and salt-sensitive varieties. Our findings provide valuable information for enhancing the understanding of complicated mechanisms of salt tolerance in G. hirsutum seedlings and cotton salt tolerance breeding by molecular marker-assisted selection.

Toward Unravelling the Genetic Determinism of the Acquisition of Salt and Osmotic Stress Tolerance Through In Vitro Selection in Medicago truncatula

Changes in global climate and the nonstop increase in demographic pressure have provoked a stronger demand for agronomic resources at a time where land suitable for agriculture is becoming a rare commodity. They have also generated a number of abiotic stresses which exacerbate effects of diseases and pests and result in physiological and metabolic disorders that ultimately impact on yield when and where it is most needed. Therefore, a major scientific and agronomic challenge today is that of understanding and countering the impact of stress on yield. In this respect, in vitro biotechnology would be an efficient and feasible breeding alternative, particularly now that the genetic and genomic tools needed to unravel the mechanisms underlying the acquisition of tolerance to stress have become available. Legumes in general play a central role in a sustainable agriculture due to their capacity to symbiotically fix the atmospheric nitrogen, thereby reducing the need for fertilizers. They also produce grains that are rich in protein and thus are important as food and feed. However, they also suffer from abiotic stresses in general and osmotic stress and salinity in particular. This chapter provides a detailed overview of the methods employed for in vitro selection in the model legume Medicago truncatula for the generation of novel germplasm capable of resisting NaCl- and PEG-induced osmotic stress. We also address the understanding of the genetic determinism in the acquisition of stress resistance, which differs between NaCl and PEG. Thus, the expression of genes linked to growth (WEE1), in vitro embryogenesis (SERK), salt tolerance (SOS1) proline synthesis (P5CS), and ploidy level and cell cycle (CCS52 and WEE1) was upregulated under NaCl stress, while under PEG treatment the expression of MtWEE1 and MtCCS52 was significantly increased, but no significant differences were observed in the expression of genes MtSERK1 and MtP5CS, and MtSOS1 was downregulated. A number of morphological and physiological traits relevant to the acquisition of stress resistance were also assessed, and methods used to do so are also detailed.

Novel potato plants with enhanced cadmium resistance and antioxidative defence generated after in vitro cell line selection

It is of interest to apply plant tissue culture to generate plants resistant to toxic effects of cadmium (Cd) on plant growth. Callus cultures were initiated from leaf explants of micropropagated potato plantlets (Solanum tuberosum L., cv. Iwa) for in vitro selection comprising 18 different Cd treatments varying in Cd exposure timing and duration. Plantlets regenerated from two different lines of Cd-selected calli, L9 and L11, were found to exhibit enhanced resistance to 218 μM Cd compared to control (source plantlets for leaf explants used to initiate callus cultures for Cd resistance). In response to 218 μM Cd, L11 plantlets had lower levels of lipid peroxidation and hydrogen peroxide than control and L9 plantlets. In addition, antioxidative enzyme activities in L11 were generally higher than control. L11 also had a higher level of proline than control.

PEG Induces High Expression of the Cell Cycle Checkpoint Gene WEE1 in Embryogenic Callus of Medicago truncatula: Potential Link between Cell Cycle Checkpoint Regulation and Osmotic Stress

Polyethylene glycol (PEG) can be used to mimic osmotic stress in plant tissue cultures to study mechanisms of tolerance. The aim of this experiment was to investigate the effects of PEG (M.W. 6000) on embryogenic callus of Medicago truncatula. Leaf explants were cultured on MS medium with 2 mg L-1 NAA and 0.5 mg L-1 BAP for 5 months. Then, calli were transferred to the same medium further supplemented with 10% (w/v) 6000 PEG for 6 months in order to study physiological and putative molecular markers of water stress. There were no significant differences in growth rate of callus or mitotic index ± PEG although embryogenic potential of PEG treated callus was morphologically enhanced. Cells were rounder on PEG medium and cell size, nuclear size and endoreduplication increased in response to the PEG treatment. Significant increases in soluble sugar and proline accumulation occurred under PEG treatment compared with the control. Significantly, high MtWEE1 and MtCCS52 expression resulted from 6 months of PEG treatment with no significant differences in MtSERK1 or MtP5CS expression but down regulation of MtSOS expression. The results are consistent in showing elevated expression of a cell cycle checkpoint gene, WEE1. It is likely that the cell cycle checkpoint surveillance machinery, that would include WEE1 expression, is ameliorating the effects of the stress imposed by PEG.

Genetic engineering strategies for biotic and abiotic stress tolerance and quality enhancement in horticultural crops: a comprehensive review

Genetic engineering technique offers myriads of applications in improvement of horticultural crops for biotic and abiotic stress tolerance, and produce quality enhancement. During last two decades, a large number of transgenic horticultural crops has been developed and more are underway. A number of genes including natural and synthetic Cry genes, protease inhibitors, trypsin inhibitors and cystatin genes have been used to incorporate insect and nematode resistance. For providing protection against fungal and bacterial diseases, various genes like chitinase, glucanase, osmotin, defensin and pathogenesis-related genes are being transferred to many horticultural crops world over. RNAi technique has been found quite successful in inducing virus resistance in horticultural crops in addition to coat protein genes. Abiotic stresses such as drought, heat and salinity adversely affect production and productivity of horticultural crops and a number of genes encoding for biosynthesis of stress protecting compounds including mannitol, glycine betaine and heat shock proteins have been employed for abiotic stress tolerance besides various transcription factors like DREB1, MAPK, WRKY, etc. Antisense gene and RNAi technologies have revolutionized the pace of improvement of horticultural crops, particularly ornamentals for color modification, increasing shelf-life and reducing post-harvest losses. Precise genome editing tools, particularly CRISPR/Cas9, have been efficiently applied in tomato, petunia, citrus, grape, potato and apple for gene mutation, repression, activation and epigenome editing. This review provides comprehensive overview to draw the attention of researchers for better understanding of genetic engineering advancements in imparting biotic and abiotic stress tolerance as well as on improving various traits related to quality, texture, plant architecture modification, increasing shelf-life, etc. in different horticultural crops.

Respuesta de cultivares de Musa spp. al estrés hídrico in vitro inducido con polietilenglicol 6000

Los plátanos y bananos son cultivos sensibles al déficit hídrico. Las sequías cada vez más prolongadas sugieren la necesidad de obtener plantas tolerantes a este factor; la selección temprana de estas plantas, comparada con la selección en campo, permite ahorrar tiempo y trabajar con mayores volúmenes de individuos. Para ello es conveniente contar con cultivares patrones cuya respuesta al déficit hídrico in vitro sea favorable. El objetivo del presente trabajo fue determinar la respuesta de cultivares de Musa spp. con diferente composición genómica al estrés hídrico inducido in vitro con polietilenglicol 6000 (PEG-6000). Se estudiaron los cultivares ‘Pelipita’ (ABB), ‘Manzano’ (AAB) y ‘Grande naine’ (AAA). El estrés se indujo con 30 g/L de PEG-6000 en medio de cultivo semisólido de multiplicación. A los 30 días se evaluaron variables indicadoras de estrés morfológicas (altura y número de brotes por explante), fisiológicas (masa fresca y masa seca) y bioquímicas (contenido prolina, peróxido de hidrógeno y malondialdehido). En el cultivar ‘Pelipita’ se afectó solamente la altura de las plantas, mientras que en los demás se afectaron todas las variables excepto la masa seca en el ‘Manzano’. En este último y en el ‘Grande naine’ se incrementó la prolina, el peróxido de hidrógeno y el malondialdehido, lo que evidenció un mayor estrés oxidativo y daño en las membranas celulares. Los cultivares estudiados, pudieran emplearse como controles de tolerancia (‘Pelipita’) y sensibilidad (‘Grande naine’ y ‘Manzano’) en la selección in vitro de plantas tolerantes a la sequía, en futuros programas de mejoramiento genético.

An update on nitric oxide and its benign role in plant responses under metal stress

Pollution due to heavy metal(loid)s has become common menace across the globe. This is due to unprecedented frequent geological changes coupled with increasing anthropogenic activities, and population growth rate. Heavy metals (HMs) presence in the soil causes toxicity, and hampers plant growth and development. Plants being sessile are exposed to a variety of stress and/or a network of different kinds of stresses throughout their life cycle. To sense and transduce these stress signal, the signal reactive nitrogen species (RNS) particularly nitric oxide (NO) is an important secondary messenger next to only reactive oxygen species (ROS). Nitric oxide, a redox active molecule, colourless simple gas, and being a free radical (NO) has the potential in regulating multiple biological signaling responses in a variety of plants. Nitric oxide can counteract HMs-induced ROS, either by direct scavenging or by stimulating antioxidants defense team; therefore, it is also known as secondary antioxidant. The imbalance or cross talk of/between NO and ROS concentration along with antioxidant system leads to nitrosative and oxidative stress, or combination of both i.e., nitro-oxidative stress. Endogenous synthesis of NO also takes place in plants in the presence of heavy metals. During HM stress the different organelles of plant cells can biosynthesize NO in parallel to the ROS, such as in mitochondria, chloroplasts, peroxisomes, cytoplasm, endoplasmic reticulum and apoplasts. In view of the above, an effort has been made in the present review article to trace current knowledge and latest advances in chemical properties, biological roles, mechanism of NO action along with the physiological, biochemical, and molecular changes that occur in plants under different metal stress. A brief focus is also carried on ROS properties, roles, and their production.

Marine Actinobacteria as a source of compounds for phytopathogen control: An integrative metabolic-profiling / bioactivity and taxonomical approach

Marine bacteria are considered as promising sources for the discovery of novel biologically active compounds. In this study, samples of sediment, invertebrate and algae were collected from the Providencia and Santa Catalina coral reef (Colombian Caribbean Sea) with the aim of isolating Actinobateria-like strain able to produce antimicrobial and quorum quenching compounds against pathogens. Several approaches were used to select actinobacterial isolates, obtaining 203 strains from all samples. According to their 16S rRNA gene sequencing, a total of 24 strains was classified within Actinobacteria represented by three genera: Streptomyces, Micromonospora, and Gordonia. In order to assess their metabolic profiles, the actinobacterial strains were grown in liquid cultures, and LC-MS-based analyses from ethyl acetate fractions were performed. Based on taxonomical classification, screening information of activity against phytopathogenic strains and quorum quenching activity, as well as metabolic profiling, six out of the 24 isolates were selected for follow-up with chemical isolation and structure identification analyses of putative metabolites involved in antimicrobial activities.

Establecimiento de un sistema de selección in vitro de variedades venezolanas de arroz (Oryza sativa L.) resistentes al hongo Pyricularia grisea

El arroz, luego del trigo, es el cereal más importante del mundo, sin embargo, es susceptible al ataque de numerosos patógenos, siendo Pyricularia grisea, el más dañino. Este trabajo estableció un sistema de selección in vitro de variedades venezolanas a P. grisea, optimizando el sistema de regeneración por embriogénesis somática (inducción, regeneración y estrés por desecación), sometiendo el callo embriogénico (E) a presión de selección del filtrado crudo “FC” a través de cambios a la misma concentración “MC” o por incrementos progresivos en la concentración “IPC”, obteniendo plantas tolerantes al fitopatógeno. El máximo porcentaje de inducción de callo embriogénico oscilo entre 30-65 %, en las cuatro variedades (Araure-4 y Venezuela 21: 1 mg.L-1 + 2 mg.L-1 K; Cimarrón: 3 mg.L-1 + 2 mg.L-1 K; Centauro: 1 mg.L-1 + 2 mg.L-1 BAP), mientras que la regeneración estuvo entre 44 y 52 % con 0.5 mg.L-1 + 2 mg.L-1 BAP a 48 h de desecación para Centauro y 24 h para las otras tres variedades. La frecuencia regenerativa de los callos E disminuyo a medida que se incrementó la concentración del FC, independientemente del método de presión selectiva. El promedio de plantas diferenciada por variedad, dependió del método de presión usado, siendo el sistema IPC (25 % para Centauro y 50 % para las otras tres variedades) el que mostro los resultados más favorables, evidenciándose que para las condiciones de los sistemas selectivos de FC evaluados, la resistencia expresada a nivel de planta in vivo no corresponde a la encontrada in vitro.

Genetic analysis of proline concentration under osmotic stress in sunflower (Helianthus annuus L.)

Proline concentration has been often suggested as an indicator of osmotic stress. A better understanding of the genetics of this trait is however needed. In the present study, proline concentration has been assessed, together with root and stem growth, potassium, calcium and total soluble sugars concentration and stress injury symptoms, in seedlings of sunflower hybrids and their parents grown under control and osmotic conditions. Proline strongly accumulated with osmotic stress. Its concentration exhibited a large variation among genotypes and was higher in hybrids than in parental lines. A positive association was noted between proline concentration and osmotic adjustment that was reflected in a reduction of osmotic stress induced injury, as showed by the reduced number of calli in the hybrids with higher proline concentration. Broad and narrow sense heritability was higher under osmotic stress suggesting applying the selection in osmotic stress condition. In the control treatment, dominance effects explained most of the genetic variation for proline concentration while under osmotic stress both dominance and additive variance were high. The importance of dominance and additive effects suggested that several genomic regions are controlling this trait. Good general combiners, presumably carrying positive additive alleles affecting proline concentration, were identified.

Genetically modified (GM) crops: milestones and new advances in crop improvement

New advances in crop genetic engineering can significantly pace up the development of genetically improved varieties with enhanced yield, nutrition and tolerance to biotic and abiotic stresses. Genetically modified (GM) crops can act as powerful complement to the crops produced by laborious and time consuming conventional breeding methods to meet the worldwide demand for quality foods. GM crops can help fight malnutrition due to enhanced yield, nutritional quality and increased resistance to various biotic and abiotic stresses. However, several biosafety issues and public concerns are associated with cultivation of GM crops developed by transgenesis, i.e., introduction of genes from distantly related organism. To meet these concerns, researchers have developed alternative concepts of cisgenesis and intragenesis which involve transformation of plants with genetic material derived from the species itself or from closely related species capable of sexual hybridization, respectively. Recombinase technology aimed at site-specific integration of transgene can help to overcome limitations of traditional genetic engineering methods based on random integration of multiple copy of transgene into plant genome leading to gene silencing and unpredictable expression pattern. Besides, recently developed technology of genome editing using engineered nucleases, permit the modification or mutation of genes of interest without involving foreign DNA, and as a result, plants developed with this technology might be considered as non-transgenic genetically altered plants. This would open the doors for the development and commercialization of transgenic plants with superior phenotypes even in countries where GM crops are poorly accepted. This review is an attempt to summarize various past achievements of GM technology in crop improvement, recent progress and new advances in the field to develop improved varieties aimed for better consumer acceptance.

Transcriptome analysis reveals translational regulation in barley microspore-derived embryogenic callus under salt stress

Transcriptome analysis of barley embryogenic callus from isolated microspore culture under salt stress uncovered a role of translation inhibition and selective activation of stress-specific proteins in cellular defense. Soil salinity is one of the major abiotic stresses which constrains the plant growth and reduces the productivity of field crops. In this study, it was observed that the salt stress in barley isolated microspore culture impacted not only on the quantity of embryogenic callus but also on the quality for later differentiation. The barley microspore-derived embryogenic callus, a transient intermediate form linked cells and plants, was employed for a global transcriptome analysis by RNA sequencing to provide new insights into the cellular adaptation or acclimation to stress. A total of 596 differentially expressed genes (DEGs) were identified, in which 123 DEGs were up-regulated and 473 DEGs were down-regulated in the embryogenic callus produced from microspore culture under salt stress as compared to the control conditions. KEGG pathway analysis identified 'translation' (27 DEGs; 12.56 %) as the largest group and followed by 'folding, sorting and degradation' (25 DEGs; 11.63 %) in 215 mapped metabolic pathways. The results of RNA-Seq data and quantitative real-time polymerase chain reaction validation showed that the genes related to translation regulation (such as eIF1A, RPLP0, RPLP2, VARS) were down-regulated to control general protein synthesis, and the genes related to endoplasmic reticulum stress response (such as small heat shock protein genes) were selectively up-regulated against protein denaturing during microspore embryogenesis under continuous salt stress. These transcriptional remodeling might affect the essential protein synthesis for the cell development to fulfill totipotency under salt stress.