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.

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.

Eight sweet pepper plant samples showing viral and viral like symptoms were collected from open field and used for detecting viral infections through biological, serological and biochemical methods. DAS-ELISA, DBIA and TPIA have relative effectiveness for detecting parenchymal viruses (CMV, TMV and PVY) and vascular virus (TYLCV), and the DAS-ELISA and TPIA are found more efficient (87.5%) than DBIA (78.1%). The examined leaf samples were found co-infected with different mixed types of viruses including (CMV, TMV, PVY and TYLCV), (CMV, PVY and TYLCV), (TMV, PVY and TYLCV) and (TMV and TYLCV) that enhanced different degrees of severe external symptoms. There are 2 out of 8 samples infected with Phytoplasma sp. by Diene’s stain and PCR using generated 16S rDNA gene primer with expected amplicon size of 680 bp. The co-infections with various viruses and phytoplasma has 12.5% frequency that reduced the levels of protein content, peroxidase and polyphenol oxidase activity quantitatively and qualitatively in 2 samples in comparison with other mixed categories. The sweet pepper plant can be considered as a reservoir for parenchymal and vascular viruses and Phytoplasma sp. due to the synergistic and antagonistic effects causing unusual and unpredictable biological and epidemiological, viral and viral-like via host biochemical effects.

Globally, root rot disease of tomato plants caused by Sclerotium rolfsii is a severe disease leading to the death of infected plants. The effect of some commercial antiseptics and disinfectant agents, such as chloroxylenol (10%), phenic (10%) and formulated phenol (7%) on the control of root rot pathogen and its impact on growth and chemical constituents of tomato seedlings cv. Castle Rock were investigated in vitro and in vivo. The antifungal activity was measured in vitro following the poisoned food technique at different concentrations of 1000, 2000, 3000 and 4000 µL/L. Disinfectant agents and atrio (80%) were tested in vivo by soaking 20-day-old tomato seedlings in four concentrations of 125, 250, 500 and 1000 µL/100 mL water for 5 min and thereafter planting in soil infested by S. rolfsii. Fresh and dry weight, shoot and root length, and chemical constituents of tomato seedlings infected by S. rolfsii were investigated at 35 days after planting (DAP). Experimental results indicated that chloroxylenol (10%) was the most effective on fungus in vitro, recorded an effective concentration (EC₅₀ = 1347.74 µL/L) followed by phenic (10%) (EC₅₀ = 1370.52 µL/L) and formulated phenol (7%) (EC₅₀ = 1553.59 µL/L). In vivo, atrio (80%) and disinfectant agents at different concentrations significantly (p ≤ 0.05) reduced disease incidence, increased shoot and root lengths and increased dry and fresh weight. Additionally, it significantly increased chlorophyll a, chlorophyll b, total carotenoids, total carbohydrates, total proteins, and total phenols. The highest reduction of root rot incidence and increase tomato growth parameters, as well as chemical compositions, were recorded on tomato seedlings treated with atrio (80%) as well as formulated phenol (7%) at different concentrations, followed by chloroxylenol (10%) at 125 and 250 µL/100 mL, whereas phenic (10%) was found to be the least effective treatment. Therefore, the application of formulated phenol (7%) could be commercially used to control tomato root rot diseases and increase the quality and quantity of tomato plants since it is promising against the pathogen, safe, and less expensive than fungicides.

Bacterial viruses are currently used as a biocontrol agent for bacterial plant disease management. The evaluation of formulated bacteriophages mixed with carriers as a biocontrol agent showed efficacy and reduced disease symptoms (halo blight spots HBS) on the leaves of bean plants caused by Ps. syringae. It was isolated on nutrient agar. The single colonies of Ps. syringae appeared flat and produced fluorescent diffusible pigment on the king 's B medium as well as phylogenetically based on 16s RNA gene 726 bp by PCR. Two formulated bacteria viruses were applied as a biocontrol agent to control HBS disease. A complete randomized design was adapted in two experiments with three replications under greenhouse and open field conditions. The formulated bacteria viruses (skim milk and corn flour) significantly decreased the severity of the disease under greenhouse between 88.8 and 85.3 % and under open field conditions between 74.9 and 62.0 %, in comparison to pure bacteria viruses and copper oxychloride treatments to 83.3 and 76.3% in the greenhouse in addition to 74.9 and 62.0 % in open field respectively. The use of SM and CF for disease control experiments enhanced phage lifetime by up to 120 hours and phage density by Log 1.5 and 1.2 PFU/mL in the greenhouse and open field, correspondingly. The formulated bacteriophages (CF and SM) compared with bacteria viruses and copper oxychloride in a greenhouse and open fields showed the lowest HBS and AUDPC values. These phages may be effectively used to control halo blight disease.

The second sugar crop of sugar production after sugar cane worldwide is sugar beet (Beta vulgaris L.). This plant is subjected to the infestation of several insect pests that cause considerable damage, especially leafhoppers, that can transmit phytopathogens (e.g., phytoplasma). In this work, we identified and described the leafhopper, Hebata (Alboneurasca) decipiens, in addition to detection and molecular identification of Candidatus Phytoplasma that was transmitted by this leafhopper on sugar beet plants from naturally infected sugar beet plants to an uninfected one. The 16S rDNA gene from phytoplasma was amplified by a nested polymerase chain reaction (PCR) assay and directly sequenced using specific primer pairs DNA fragments. The resulting sequences were analyzed and compared with another phytoplasma sequence available at GenBank sequences performing BLAST using DNAMAN.