Uncovering salt tolerance mechanisms in pepper plants: a physiological and transcriptomic approach

Revitalizing agriculture: next-generation genotyping and -omics technologies enabling molecular prediction of resilient traits in the Solanaceae family

This review highlights -omics research in Solanaceae family, with a particular focus on resilient traits. Extensive research has enriched our understanding of Solanaceae genomics and genetics, with historical varietal development mainly focusing on disease resistance and cultivar improvement but shifting the emphasis towards unveiling resilience mechanisms in genebank-preserved germplasm is nowadays crucial. Collecting such information, might help researchers and breeders developing new experimental design, providing an overview of the state of the art of the most advanced approaches for the identification of the genetic elements laying behind resilience. Building this starting point, we aim at providing a useful tool for tackling the global agricultural resilience goals in these crops.

Enhancing the nutritional value of sweet bell pepper through moderate NaCl salinity

Salinity presents a significant obstacle to crop productivity, particularly in dry and semi-arid regions. Sweet bell pepper (Capsicum annuum L.), a widely grown and consumed horticultural crop, is especially vulnerable to salinity. Consequently, it is vital to determine the salinity threshold that impacts bell pepper growth and quality, enabling sustainable production in salinized areas. This study aimed to evaluate the effects of varying sodium chloride concentrations (0, 50, and 75 mM) on bell pepper growth, nutritional value, and phytochemical composition, aiming to identify the adaptable threshold in salinized environments. The results suggested that the application of 75 mM NaCl not only had no adverse impact on fruit quality in terms of biomolecules and phytochemicals but also led to significant improvements. Specifically, under these conditions, there was a remarkable increase, in respect to control, in total protein (TPRO by 50 %), total carbohydrates (TCARB by 18 %), lycopene (LIC by 68 %), total Carotenoids (TCAR by 13 %), and total phenols (TPHE by 18 %) in terms of antioxidants.In contrast, the content of ascorbic acid and antioxidant activities remained consistent. Moderate salt stress exhibited the most positive influence on sweet bell pepper quality, leading to higher concentrations of essential nutrients and nutraceutical compounds, including minerals, phenolic acids, and flavonoids.

Differential gene expression patterns and physiological responses improve adaptation to high salinity concentration in pepper accessions

High salinity decreases the productivity of crops worldwide. Pepper is particularly sensitive to high salt concentrations. Herein, we subjected three tolerant pepper accessions (C12, B14 and A25) to high sodium chloride concentration (70 mM NaCl). The aerial and root biomass, leaf and root osmotic potential (Ψπ ), Na+ , Cl- , K+ and proline concentrations and the relative expression of the putative genes CaSOS1, CaHKT1, three CaNHXs and CaP5CS were measured. Different salinity tolerance strategies depending on the pepper accession were identified. In C12, tolerance was attributed to the accumulation of Na+ in vacuoles and endosomes by the activation of vacuolar CaNHXs genes and the reduction in Ψπ ; additionally, the activation of CaHKT1 and CaSOS1 in leaves and roots moved and accumulated Na+ ions in the xylem and xylem parenchyma cells (XPC) as well as expulsed it out of the root cells. A25 accession, on the contrary, was specialized in compartmentalizing Na+ ions in root and leaf vacuoles and root XPC by the up-regulation of CaNHXs and CaHKT1, respectively, avoiding a toxic accumulation in leaves. Finally, B14 accession moved and accumulated Na+ in xylem and XPC, reducing its concentration in roots by the activation of CaSOS1 and CaHKT1. This study shade light on different tolerance mechanisms of pepper plants to overcome salt stress.

New Insights Into Short-term Water Stress Tolerance Through Transcriptomic and Metabolomic Analyses on Pepper Roots

In the current climate change scenario, water stress is a serious threat to limit crop growth and yields. It is necessary to develop tolerant plants that cope with water stress and, for this purpose, tolerance mechanisms should be studied. NIBER® is a proven water stress- and salt-tolerant pepper hybrid rootstock (Gisbert-Mullor et al., 2020; López-Serrano et al., 2020), but tolerance mechanisms remain unclear. In this experiment, NIBER® and A10 (a sensitive pepper accession (Penella et al., 2014)) response to short-term water stress at 5 h and 24 h was studied in terms of gene expression and metabolites content in roots. GO terms and gene expression analyses evidenced constitutive differences in the transcriptomic profile of NIBER® and A10, associated with detoxification systems of reactive oxygen species (ROS). Upon water stress, transcription factors like DREBs and MYC are upregulated and the levels of auxins, abscisic acid and jasmonic acid are increased in NIBER®. NIBER® tolerance mechanisms involve an increase in osmoprotectant sugars (i.e., trehalose, raffinose) and in antioxidants (spermidine), but lower contents of oxidized glutathione compared to A10, which indicates less oxidative damage. Moreover, the gene expression for aquaporins and chaperones is enhanced. These results show the main NIBER® strategies to overcome water stress.

Effects of Conventional and Bokashi Hydroponics on Vegetative Growth, Yield and Quality Attributes of Bell Peppers

Due to consumers' awareness and concern about nutrition and health in different parts of the world, the adoption of organic hydroponics is increasing. This has led to a search for organic nutrient media. One of the viable nutrient sources for organic hydroponics is bokashi compost. The principal objective of this study was to compare the performance of 10% bokashi hydroponics with convention hydroponics for bell pepper production. The different hydroponics influenced vegetative growth parameters largely due to considerable differences in the mineral elements in both hydroponic systems. Stems of conventionally grown plants were significantly (p ≤ 0.05) thicker (10.2 mm) compared to those of the bokashi grown plants (7.3 mm). Conventionally grown plants had significantly (p ≤ 0.05) higher photosynthetic performance than bokashi grown plants; normalized difference vegetation index (NDVI) (78.80 versus 67.49), soil plant analysis development (SPAD; 73.89 versus 38.43), and quantum yield (QY; 0.64 versus 0.49). Leaf superoxide dismutase (SOD) activity in the leaves of bokashi grown plants (0.32 units/mg protein) was significantly (p ≤ 0.05) lower than in the leaves of conventionally grown plants (0.37 units/mg protein). This also corresponded to significantly (p ≤ 0.05) higher leaf sap content in the conventionally grown plant than bokashi grown plants. Furthermore, conventional hydroponics yielded three-fold greater pepper fruit per plant compared to bokashi. After 14 days of storage at 7 °C and 95% relative humidity, the firmness of both groups declined, especially for the bokashi grown fruit (27.73 shore unit), which was significantly lower compared to conventionally grown fruit (35.65 shore unit). However, there was an increase in carotenoid content in fruit grown in both hydroponic systems after storage. In conclusion, although bell pepper plant was successfully cultivated in bokashi hydroponics, the plant performance, fruit yield and postharvest quality were lower than conventional hydroponics. We believe that this study and its approach will provide future research with baseline information on optimizing media of bokashi hydroponics to produce bell pepper.