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Green nanotechnology has emerged as a viable option for the production of nanoparticles. The purpose of the current investigation was to synthesize silver nanoparticles (AgNPs) using Eucalyptus camaldulensis and Terminalia arjuna extracts, as well as their combinations, as green reducing and capping agents. The parameters (concentration of silver nitrate solution and plant extract, time, pH, and temperature) were optimized for maximal yields, regulated size, and stability of silver nanoparticles. The ultraviolet–visible spectrophotometer (UV-Vis) and the surface plasmon resonance band (SPR) were used to validate the synthesis of AgNPs. The size, shape, and stability of nanoparticles were assessed using a zeta analyzer and a scanning electron microscope (SEM). The biomolecules responsible for the reduction of silver ion (Ag+) and the stability of silver nanoparticles generated with the plant extracts were identified using Fourier-transform infrared spectroscopy (FTIR). The agar-well diffusion method was used to test the antimicrobial activity of biosynthesized nanoparticles against Bacillus subtilis, Staphylococcus aureus, Pasteurella multocida, and Escherichia coli. When 1 mM of silver nitrate (AgNO3) was added to plant extracts and incubated for 60 min at 75°C in a neutral medium, maximum nanoparticles were produced. Biosynthesized silver nanoparticles were stable, spherical, and monodispersed according to zeta potential and scanning electron microscopy. Silver nanoparticles synthesized with combination 2 and T. arjuna showed the highest zone of inhibition (16 mm) against B. subtilis while combination 3 showed the largest zone of inhibition against S. aureus (17 ± 0.8). It was concluded that greenly produced silver nanoparticles showed good antibacterial activity while causing negligible cytotoxicity.

This study reports the characterization of protein elicitor PeBb1 derived from entomopathogenic fungus Beauveria bassiana ARSEF-2860 strain and its putative role in induced systemic resistance in Brassica rapa ssp. pekinensis against green peach aphid Myzus persicae. The sequence of purified elicitor protein was matched with the genomic sequence of a hypothetical protein BBA_10269 from B. bassiana ARSEF-2860 (GenBank Accession No. XP_008603588.1). The protein-encoding gene PeBb1 contained 534 bp cDNA encoding a polypeptide of 177 amino acids with a molecular mass of 19 kDa. The recombinant elicitor protein was expressed in Escherichia coli using pET-28a (+) expression vector and induced necrosis in the leaves of tobacco. The effects of elicitor protein on aphid M. persicae was determined by applying three different concentrations of PeBb1 (i.e., 26, 35, 53 µM) on B. rapa plants at 4-leaf stage and the treated plants were exposed to newly emerged (0-6 h old) apterous adult aphids. Bioassay results showed significant (p < 0.05) sub-lethal effects of the exogenous application of PeBb1 elicitor on M. persicae. Moreover, the RT-qPCR gene expression analyses showed a significant up-regulation of most of the key genes linked to ethylene (ET)-and jasmonic acid (JA)-associated plant defense pathways in elicitor-treated plants.These results not only recommend the putative utilization of PeBb1 elicitor protein in future biological pest control strategies against phloem-feeding insect pests such as M. persicae, but also help in better comprehension of the mechanisms through which beneficial fungi trigger the induced plant resistance.

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The whitefly, Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae), is one of the most damaging pests in field crops as well as in greenhouses. The present study aimed to evaluate the in vitro pathogenicity of 2 fungus strains of Beauveria bassiana (BB-72 and BB-252) and one strain of Lecanicillium lecanii (V-2) against the whitefly (B. tabaci) at 4 different temperature degrees 20, 24, 28, and 32°C, using a spray method. Three different bioassays were carried out comprised of conidial concentrations and filtrate of fungal strains, BB-72, BB-252 and V-2, and their binary combinations. The 1.5 ml of fungal filtrate was used in filtrate bioassay for each strain of fungus. Three different concentrations (1 × 10 6 , 1 × 10 7 , and 1 × 10 8 conidia ml −1 ) were used in conidial bioassay for each strain of fungus, whereas in bioassay for binary combination (1 ml conidia + 1 ml filtrate) of BB-72 × BB-72, BB-252 × BB-252, and V2 × V2 were used for these strains of fungus. According to the outcomes, the maximum mortality against whiteflies was observed on 12th day post-treatment. In conidial bioassay, the maximum mortality of B. tabaci was observed in BB-72 isolate (84%), BB-252 isolate (77%), and V-2 isolate (67%) at the highest concentration (1 × 10 8 conidia ml −1 ) at 24°C, and minimum mortality was recorded in BB-72 isolate (33%), BB-252 isolate (29%), and V-2 isolate (19%) at the lowest concentration 1 × 10 6 conidia ml −1 at 32°C on 12th day post-treatment. Infiltrate bioassay, BB-72 isolate exhibited maximum mortality (92%) at 24°C, and V-2 isolate showed minimum mortality (34%) at 32°C on 12th day post-treatment. Furthermore, in binary combination bioassay, the highest whitefly mortality was recorded in BB-72 × BB-72 isolate (87%), BB-252 × BB-252 isolate (73%), and V2 × V2 isolate (65%) at 24°C and the lowest mortality in BB-72 × BB-72 isolate (57%), BB-252 × BB-252 isolate (50%), and V2 × V2 isolate (39%) at 32°C on 12th day posttreatment. In all bioassays, the BB-72 isolate was the utmost virulent, and application of its filtrate was found to be the most impressive against B. tabaci.

Plants rely on various physiological and molecular defense mechanisms against biotic stresses such as herbivore insects. Many entomopathogenic fungi synthesize protein molecules that can trigger these plant defenses. This laboratory study characterized the bioactivity of a partially purified protein derived from Beauveria bassiana (ARSEF 2860) against whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), which is an economically important pest of agricultural and horticultural crops worldwide. Different concentrations (i.e., 0.021, 0.042 and 0.063 μM) of fungal protein were bioassayed to determine their sub-lethal effect on the survival percentage and fecundity rate of B. tabaci on tomato (Lycopersicon esculentum) plants. In addition, the putative role of this partially purified B. bassiana protein in the defense mechanisms of plant was assessed through the expression analyses of important genes related to salicylic acid (SA)—and jasmonic acid (JA)—associated pathways using RT-qPCR. Results revealed a significant suppression of the survival percentage and fecundity rate of B. tabaci by the fungal protein. Lowest survival (41%) was recorded for the highest concentration of protein (0.063 μM), whereas mean survival for the other two protein concentrations (0.042 and 0.021 μM) were 62 and 71%, respectively. Likewise, the highest and lowest mean fecundity rates were observed for the control and the highest protein concentration (i.e., 3.3 and 1.8 eggs day−1 female−1, respectively). Furthermore, the exogenous application of B. bassiana-derived protein on tomato plants strongly up-regulated the SA-related genes (PAL, PR1, BGL2 and EDS1) and slightly up-regulated the JA-related genes (AOC, AOS, OPR3 and LOX) as compared to the control plants. These findings demonstrate the putative role of this partially purified B. bassiana protein fraction in inducing systemic resistance in the tomato plants against B. tabaci, suggesting its further purification and characterization to be used as novel biological pest control tool against B. tabaci and other sap-sucking insect pests.

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