Enhancing systemic resistance in faba bean (Vicia faba L.) to Bean yellow mosaic virus via soil application and foliar spray of nitrogen-fixing Rhizobium leguminosarum bv. viciae strain 33504-Alex1.

Rhizobium spp. manifests strong nitrogen fixation ability in legumes. However, their significance as biocontrol agents and antivirals has rarely been investigated. Under greenhouse conditions, the molecularly identified nitrogen-fixing plant growth-promoting rhizobacteria (PGPR), Rhizobium leguminosarum bv. viciae strain 33504-Alex1, isolated from the root nodules of faba bean plants, was tested as a soil inoculum or a foliar application to trigger faba bean plants' resistance against Bean yellow mosaic virus (BYMV) infection. Compared to the non-treated faba bean plants, the applications of 33504-Alex1 in either soil or foliar application significantly promoted growth and improved total chlorophyll content, resulting in a considerable reduction in disease incidence and severity and the inhibition index of BYMV in the treated faba bean plants. Furthermore, the protective activities of 33504-Alex1 were associated with significant reductions in non-enzymatic oxidative stress markers [hydrogen peroxide (H2O2) and malondialdehyde (MDA)] and remarkably increased DPPH free radical scavenging activity and total phenolic content compared to the BYMV treatment at 20 days post-inoculation. Additionally, an increase in reactive oxygen species scavenging enzymes [superoxide dismutase (SOD) and polyphenol oxidase (PPO)] and induced transcriptional levels of pathogenesis-related (PR) proteins (PR-1, PR-3, and PR-5) were observed. Of the 19 polyphenolic compounds detected in faba bean leaves by high-performance liquid chromatography (HPLC) analysis, gallic and vanillic acids were completely shut down in BYMV treatment. Interestingly, the 33504-Alex1 treatments were associated with the induction and accumulation of the most detected polyphenolic compounds. Gas chromatography-mass spectrometry (GC-MS) analysis showed hexadecanoic acid 2,3-dihydroxypropyl ester, tetraneurin-A-Diol, oleic acid, and isochiapin B are the major compounds in the ethyl acetate extract of 33504-Alex1 culture filtrate (CF), suggesting it acts as an elicitor for the induction of systemic acquired resistance (SAR) in faba bean plants. Consequently, the capacity of R. leguminosarum bv. viciae strain 33504-Alex1 to enhance plant growth and induce systemic resistance to BYMV infection will support the incorporation of 33504-Alex1 as a fertilizer and biocontrol agent and offer a new strategy for crop protection, sustainability, and environmental safety in agriculture production.

Defense Responses and Metabolic Changes Involving Phenylpropanoid Pathway and PR Genes in Squash (Cucurbita pepo L.) following Cucumber mosaic virus Infection.

The current study focuses on the effects of Cucumber mosaic virus (CMV) infection on phytochemical changes and pathogenesis- and phenylpropanoid pathway-associated gene activities in squash (Cucurbita pepo L.) plants during a time course of 2 to 12 days post inoculation (dpi). The identity of the CMV isolate was confirmed by DAS-ELISA, TEM, and coat protein gene sequence. The CMV infection initially boosts and then suppresses transcript levels of the defense-related genes PR-1, PR-2, PAL, HQT, and CHS during the investigated time course compared to controls. The expression profile during the time-course study indicated that early, transient induction of PR-1 occurs during CMV infection, while CMV induced the expression of PR-2 in systemically infected squash tissues at all time points and suppressed the expression of PAL and HQT at 8-12 dpi. CHS transcript levels fluctuated between up- and down-regulation, but by 12 dpi, CHS expression reached its peak. The HPLC and GC-MS analyses of CMV-infected squash extracts revealed that different phenolic, flavonoid, and fatty acid compounds could be induced or suppressed upon CMV infection. In particular, CMV could suppress the synthesis of most phenolic compounds, specifically chlorogenic acid, possibly leading to the virus's rapid spread.

Chitosan Nanoparticles Inactivate Alfalfa Mosaic Virus Replication and Boost Innate Immunity in Nicotiana glutinosa Plants.

Plant viral infection is one of the most severe issues in food security globally, resulting in considerable crop production losses. Chitosan is a well-known biocontrol agent against a variety of plant infections. However, research on combatting viral infections is still in its early stages. The current study investigated the antiviral activities (protective, curative, and inactivation) of the prepared chitosan/dextran nanoparticles (CDNPs, 100 µg mL-1) on Nicotiana glutinosa plants. Scanning electron microscope (SEM) and dynamic light scattering analysis revealed that the synthesized CDNPs had a uniform, regular sphere shapes ranging from 20 to 160 nm in diameter, with an average diameter of 91.68 nm. The inactivation treatment was the most effective treatment, which resulted in a 100% reduction in the alfalfa mosaic virus (AMV, Acc# OK413670) accumulation level. On the other hand, the foliar application of CDNPs decreased disease severity and significantly reduced viral accumulation levels by 70.43% and 61.65% in protective and curative treatments, respectively, under greenhouse conditions. Additionally, the induction of systemic acquired resistance, increasing total carbohydrates and total phenolic contents, as well as triggering the transcriptional levels of peroxidase, pathogen-related protein-1, and phenylalanine ammonia-lyase were observed. In light of the results, we propose that the potential application of CDNPs could be an eco-friendly approach to enhance yield and a more effective therapeutic elicitor for disease management in plants upon induction of defense systems.

Antibacterial activity of three essential oils and some monoterpenes against Ralstonia solanacearum phylotype II isolated from potato.

The present study describes the possibility of using some essential oils and monoterpens as bioagents against the growth of Ralstonia solanacearum, a causal bacterium of potato brown rot disease. Eight isolates of the bacterium were recovered from infected potato tubers, showing typical symptoms of the disease, Isolates were identified as R.solanacearum phylotype II, based on biochemical and physiological characteristics, as well as, at the molecular level through PCR analysis. Three essential oils extracted from Corymbia citriodora (leaves), Cupressus sempervirens (aerial parts), and Lantana camara (aerial parts) were evaluated for their antibacterial activity against eight isolates of R. solanacearum phylotype II. Results demonstrated that L. camara essential oil (concentration 5000 µg/mL) had the highest effects against the RsMo2, RsSc1 and Rs48, with inhibition zone (IZ) values of 17.33, 16.33, and 17.50 mm, respectively, also against Rs2 (IZ 14.33 mm), and RsIs2 (IZ 16 mm). C. citriodora oil showed the highest activity against RsBe2 (IZ 14 mm), RsFr4 (IZ 13.66 mm) and RsNe1 (IZ 13.66 mm). Gas Chromatography-Mass Spectrometry (GC-MS-FID) analyzed the chemical composition of these essential oils. It was proved that L. camara leaves contains mainly trans-caryophyllene (16.24%) and α-humulene (9.55%), in C. citriodora oil were α-citronellal (56.55%), α-citronellol (14.89%), and citronellol acetate (13.04%), and in Cup. sempervirens aerial parts were cedrol (22.17%), and Δ3-carene (18.59%). Five monoterpenes were evaluated against the most resistance Ralstonia isolate RsFr5 to the three studied essential oils and found that limonene had the highest effect against it compared with the lowest thymol. The results proved the strong bio effects of the essential oil from L. camara leaves as a natural product contained monoterpenes that can inhibit the growth of tested R. solanacearum phylotype II isolates.

Antigenic and pathogenicity activities of Ralstonia solanacearum race 3 biovar 2 molecularly identified and detected by indirect ELISA using polyclonal antibodies generated in rabbits.

Eight molecular-characterized isolates of Ralstonia solanacearum from potato belonging to race 3 biovar 2, their virulence were evaluated on potato cv. Lady Rosette, tomato cv. Strain B, eggplant cv. Balady and pepper cv. Balady and showed high virulence on potato and tomato, and lower virulence on eggplant and pepper. A laboratory study conducted to produce polyclonal antibodies against the potato brown rot bacterium; R. solanacearum cells were generated in female New Zealand white rabbits. A modification were made on the technique of indirect enzyme-linked immunosorbent assay (ELISA) to improve the sensitivity of detection, including antigenic and sensitivity to R. solanacearum race 3 biovar 2 isolates. Determination of the optimum period to collect the antiserum (including, polyclonal antibodies) showed that the best collection dates were at 14, 3 and 7 days, in that order. The efficiency of the antiserum was compared among 42 isolates that cause potato brown rot disease; our polyclonal antiserum (14 days) reacted positively with all tested isolates at a dilution of 1:6.4 × 103. Data indicated the different reactions of eight R. solanacearum isolates at various dilutions (1:1.6 × 103 to 1:5.12 × 106) at 14 days against polyclonal antiserumat a concentration of approximately 1 × 108 CFU/mL and we found the lowest detection level by the indirect ELISA technique was 106 CFU/mL. Finally we recommended the reasonable sensitivity results of the ELISA technique to detect the bacterial pathogen given than the cost of this technique if much lower than that of other expensive molecular techniques.