Protective and Curative Activities of Paenibacillus polymyxa against Zucchini yellow mosaic virus Infestation in Squash Plants

Abstract

The use of microbial products as natural biocontrol agents to increase a plant’s systemic resistance to viral infections is a promising way to make agriculture more sustainable and less harmful to the environment. The rhizobacterium Paenibacillus polymyxa has been shown to have strong biocontrol action against plant diseases, but its antiviral activity has been little investigated. Here, the efficiency of the culture filtrate of the P. polymyxa strain SZYM (Acc# ON149452) to protect squash (Cucurbita pepo L.) plants against a Zucchini yellow mosaic virus (ZYMV, Acc# ON159933) infection was evaluated. Under greenhouse conditions, the foliar application of the culture filtrate of SZYM either in protective or curative treatment conditions enhanced squash growth, reduced disease severity, and decreased ZYMV accumulation levels in the treated plants when compared to the non-treated plants. The protective treatment group exhibited the highest inhibitory effect (80%), with significant increases in their total soluble carbohydrates, total soluble protein content, ascorbic acid content, and free radical scavenging activity. Furthermore, a considerable increase in the activities of reactive oxygen species scavenging enzymes (superoxide dismutase, polyphenol oxidase, and peroxidase) were also found. In addition, the induction of systemic resistance with a significant elevation in the transcriptional levels of polyphenolic pathway genes (CHS, PAL, and C3H) and pathogenesis-related genes (PR-1 and PR-3) was observed. Out of the 14 detected compounds in the GC–MS analysis, propanoic acid, benzenedicarboxylic acid, tetradecanoic acid, and their derivatives, as well as pyrrolo [1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl) were the primary ingredient compounds in the ethyl acetate extract of the SZYM-culture filtrate. Such compounds may act as elicitor molecules that induce systemic resistance against viral infection. Consequently, P. polymyxa can be considered a powerful plant growth-promoting bacterium (PGPB) in agricultural applications as well as a source of bioactive compounds for sustainable disease management. As far as we know, this is the first time that P. polymyxa has been shown to fight viruses in plants.

Foliar Application of Nanoclay Promotes Potato (Solanum tuberosum L.) Growth and Induces Systemic Resistance against Potato Virus Y

“…These data suggest that nanoclay, particularly of the Egyptian type, plays a function in the up-regulation of the PPO genes in potato plants, which is an important component of the plant’s defense strategy against PVY infection. As a consequence, the overexpression of PPO in a variety of plants has been reported to possess defensive capabilities against bacterial infection [ 69 ], fungal infection [ 70 ], and viral infection [ 71 ] in different plant species. Furthermore, the results showed a significant up-regulation in the POX level upon PVY infection and nanoclay treatments ( Figure 7 ).…”

Ocimum basilicum-Mediated Synthesis of Silver Nanoparticles Induces Innate Immune Responses against Cucumber Mosaic Virus in Squash

“…Plant viral infections are characterized by the over- and un-controlled expression of reactive oxygen species, which causes oxidative stress in the cell and may interfere with many vital plant processes [ 78 , 79 ]. As shown in Figure 8 , the PPO enzyme was enhanced by about 38% in the CMV treatment (0.18 ± 0.02 µM/g f. wt) compared to the Mock plant group (0.13 ± 0.02 µM/g f. wt), which could be attributed to the initial squash response to the viral infection, which is in line with ZYMV infection in the same plant [ 34 ]. In the same regard, the Ag-NPs enhanced the enzyme activity to 0.15 ± 0.01 and 0.18 ± 0.02 µM/g f. wt for pre-CMV and post-CMV treatments, respectively.…”

“…The results ( Figure 6 A) indicated a slight increase in the total soluble carbohydrate contents by about 38% in the CMV treatment group (1.8 ± 0.5 mg/g d. wt) compared to mock-treatment plants (1.3 ± 0.1 mg/g d. wt). In contrast, many studies have found that plant viral infection reduces the total soluble carbohydrate content [ 34 , 63 , 64 ]. The findings are consistent with those of Gonçalves et al [ 65 ], who discovered that the sugarcane yellow leaf virus (ScYLV) enhanced the total soluble glucose content of sugarcane.…”

“…The impact of Ag-NPs applications upon free radical scavenging activity was evaluated, as described previously [ 34 ]. Briefly, 2 mL of DPPH (2,2-Diphenyl-1-picrylhydrazyl, 0.05 M in methanol) was added to 100 µL of plant extract prepared in phosphate buffer pH 7.0 and incubated at 25 °C for 30 min.…”

“…The impact of Ag-NPs upon the total soluble protein (TSP) and total soluble carbohydrate (TSC) in the treatment plant groups under the CMV challenge were evaluated and compared to control plant groups as described in detail [ 34 ]. The TSP was evaluated according to the Bradford method [ 37 ] standard reference protein of bovine serum albumin.…”