The present work reveals the beneficial role of sodium nitroprusside (SNP; NO donor concentration: 50 and 100 µM) in mitigation of water stress accompanied by a reduction in viral disease incidence in tomato plants subjected to deficit irrigation. The plants were grown under two irrigation regimes: well-watered (WW; irrigated after the depletion of 55–60% of available soil water) and water deficit (WD; irrigated after the depletion of 85–90% of available soil water) in two seasons of 2018 and 2019. The results indicated that under water stress conditions, plant growth, chlorophyll, relative water content (RWC), and fruit yield were decreased. Conversely, water stress significantly increased the MDA, proline, soluble sugars, and antioxidant enzymes’ activities. Moreover, it was obvious a negligible increase in the fruit content from NO2 and NO3. Water-deficit stress, however, had a positive impact on reducing the percentage of viral disease (TMV and TYLCV) incidence on tomato plants. Similarly, SNP application in the form of foliar spray significantly reduced the disease incidence, the severity, and the relative concentrations of TMV and TYLCV in tomato plants raised under both WW and WD conditions. The treatment of SNP at 100 µM achieved better results and could be recommended to induce tomato plant tolerance to water stress. Thus, the present work highlights the role of NO (SNP) in the alleviation of water stress in tomato plants and subsequent reduction in viral disease incidence during deficit irrigation.

Despite the role of γ-aminobutyric acid (GABA) in plant tolerance to chilling stress having been widely discussed in the seedling stage, very little information is clear regarding its implication in chilling tolerance during the reproductive stage of the plant. Here, we investigated the influence of GABA (1 and 2mM) as a foliar application on tomato plants (Solanum lycopersicum L. cv. Super Marmande) subjected to chilling stress (5°C for 6h/day) for 5 successive days during the flowering stage. The results indicated that applied GABA differentially influenced leaf pigment composition by decreasing the chlorophyll a/b ratio and increasing the anthocyanin relative to total chlorophyll. However, carotenoids were not affected in both GABA-treated and non-treated stressed plants. Root tissues significantly exhibited an increase in thermo-tolerance in GABA-treated plants. Furthermore, applied GABA substantially alleviated the chilling-induced oxidative damage by protecting cell membrane integrity and reducing malondialdehyde (MDA) and H2O2. This positive effect of GABA was associated with enhancing the activity of phenylalanine ammonia-lyase (PAL), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX). Conversely, a downregulation of peroxidase (POX) and polyphenol oxidase (PPO) was observed under chilling stress which indicates its relevance in phenol metabolism. Interesting correlations were obtained between GABA-induced upregulation of sugar metabolism coinciding with altering secondary metabolism, activities of antioxidant enzymes, and maintaining the integrity of plastids’ ultrastructure Eventually, applied GABA especially at 2mM improved the fruit yield and could be recommended to mitigate the damage of chilling stress in tomato plants.

Plant diseases are biotic stresses that restrict crop plants’ ability to develop and produce. Numerous foliar diseases, such as chocolate spots, can cause significant production losses in Vicia faba plants. Certain chemical inducers, including salicylic acid (SA), oxalic acid (OA), nicotinic acid (NA), and benzoic acid (BA), were used in this study to assess efficacy in controlling these diseases. A foliar spray of these phenolic acids was used to manage the impacts of the biotic stress resulting from disease incidence. All tested chemical inducers resulted in a significant decrease in disease severity. They also enhanced the defense system of treated plants through increasing antioxidant enzyme activity (Peroxidase, polyphenol oxidase, β-1, 3-glucanase, and chitinase) compared to the corresponding control. Healthy leaves of faba plants recorded the lowest (p < 0.05) values of all antioxidant activities compared to those plants infected by Botrytis fabae. Moreover, the separation of proteins using SDS-PAGE showed slight differences among treatments. Furthermore, foliar spray with natural organic acids reduced the adverse effects of fungal infection by expediting recovery. The SA (5 mM) treatment produced a pronounced increase in the upper, lower epidermis, palisade thickness, spongy tissues, midrib zone, length, and width of vascular bundle. The foliar application with other treatments resulted in a slight increase in the thickness of the examined layers, especially by benzoic acid. In general, all tested chemical inducers could alleviate the adverse effects of the biotic stress on faba bean plants infected by Botrytis fabae.

Maize lethal necrosis (MLN) is a devastating disease of maize caused by synergistic infection with maize chlorotic mottle virus (MCMV) and at least one potyvirid (e.g., sugarcane mosaic virus, SCMV). MLN results in leaf necrosis, premature aging, and even whole plant death and can cause up to 100% losses in yield. MLN has emerged worldwide and resulted in serious loss in maize production. Over the past decade, extensive research has been conducted to understand the epidemic and pathogenic mechanisms of MLN. In this review, we summarize recent findings in understanding the biological functions of proteins from both viruses and discuss recent advances in molecular plant-virus interactions, particularly the co-evolutionary arms race between maize anti-viral defense and viral pathogenesis (counter-defense). Based on recent research progress, we discuss how to combine different strategies for enhancing the effectiveness of maize resistance to MCMV/SCMV, and the possible approaches for effective control of MLN.

Plant systemic resistance induced by natural product is an alternative technique of disease management. Riboflavin (vitamin B2) usually used as abiotic elicitor to improve the plant immunity against different pathogens. This work aimed to explore the efficiency of three riboflavin concentrations (0.5, 2.5, and 5 mM) to enhance resistance toward Tobacco Mosaic Virus (TMV) in tomato plants. Our results showed that exogenous application of 2.5mM riboflavin, 5 days before virus challenge was the most effective concentration, which provided a reduction in disease incidence and disease severity by 80% and 75%, respectively. Furthermore, obtained results were confirmed by using DAS-ELISA test, which showed that concentration 2.5 mM of riboflavin decreased the virus concentrations by 46.4% in treated-inoculated plants. It was remarked that exogenous application of 2.5 mM riboflavin showed a positive effect on some plant growth parameters either in presence or absence of TMV challenge. The plant height and number of leaves per plant were significantly improved in treated-inoculated plants about 30% and in compared to the infected control 78%. In time course investigation, 2.5mM riboflavin treatment reduced the virus symptoms particularly at 9 th day, where after the symptoms become evident. In addition, expression of phenylalanine ammonia-lyase (PAL) and pathogenesis-related protein (PR10), which are the markers of systemic acquired resistance (SAR), were rapidly increased in inoculated-treated tomato from 1-3 days after treatment. Moreover, the results of the biochemical changes analysis revealed that, the levels of the defense markers including peroxidase (PO), and polyphenol oxidase (PPO) were increased four days after of treatment and reached maximum levels at 8 days in the treated-inoculated plants. In conclusion, it could be suggesting that riboflavin exerted a great influence on TMV disease, as indicated by reduction of disease symptoms as well as enhancement of biochemical changes in plant defense against infection with TMV.