Jian-Gang Li

Effect of Seed Treatment by Cold Plasma on the Resistance of Tomato to Ralstonia solanacearum (Bacterial Wilt)

This study investigated the effect of cold plasma seed treatment on tomato bacterial wilt, caused by Ralstonia solanacearum (R. solanacearum), and the regulation of resistance mechanisms. The effect of cold plasma of 80W on seed germination, plant growth, nutrient uptake, disease severity, hydrogen peroxide (H2O2) concentration and activities of peroxidase (POD; EC 1.11.1.7), polyphenol oxidase (PPO; EC 1.10.3.2) and phenylalanine ammonia lyase (PAL; EC 4.3.1.5) were examined in tomato plants. Plasma treatment increased tomato resistance to R. solanacearum with an efficacy of 25.0%. Plasma treatment significantly increased both germination and plant growth in comparison with the control treatment, and plasma-treated plants absorbed more calcium and boron than the controls. In addition, H2O2 levels in treated plants rose faster and reached a higher peak, at 2.579 µM gFW−1, 140% greater than that of the control. Activities of POD (421.3 U gFW−1), PPO (508.8 U gFW−1) and PAL (707.3 U gFW−1) were also greater in the treated plants than in the controls (103.0 U gFW−1, 166.0 U gFW−1 and 309.4 U gFW−1, respectively). These results suggest that plasma treatment affects the regulation of plant growth, H2O2 concentration, and POD, PPO and PAL activity in tomato, resulting in an improved resistance to R. solanacearum. Consequently, cold plasma seed treatment has the potential to control tomato bacterial wilt caused by R. solanacearum.

PopW of Ralstonia solanacearum, a new two-domain harpin targeting the plant cell wall

Harpins are extracellular glycine-rich proteins eliciting a hypersensitive response (HR). In this study, we identified a new harpin, PopW, from Ralstonia solanacearum strain ZJ3721. This 380-amino-acid protein is acidic, rich in glycine and serine, and lacks cysteine. When infiltrated into the leaves of tobacco (non-host), PopW induced a rapid tissue collapse via a heat-stable but protease-sensitive HR-eliciting activity. PopW has an N-terminal harpin domain (residues 1-159) and a C-terminal pectate lyase (PL) domain (residues 160-366); its HR-eliciting activity depends on its N-terminal domain. Analyses of subcellular localization and plasmolysis demonstrated that PopW targeted the onion cell wall. This was further confirmed by its ability to specifically bind to calcium pectate, a major component of the plant cell wall. However, PopW had no detectable PL activity. Western blotting revealed that PopW was secreted by the type III secretion system in an hrpB-dependent manner. Gene sequencing indicated that popW is conserved among 20 diverse strains of R. solanacearum. A popW-deficient mutant retained the ability of wild-type strain ZJ3721 to elicit HR in tobacco and to cause wilt disease in tomato (a host). We conclude that PopW is a new cell wall-associated, hrpB-dependent, two-domain harpin that is conserved across the R. solanacearum species complex.

Characterization of chitinase secreted by Bacillus cereus strain CH2 and evaluation of its efficacy against Verticillium wilt of eggplant

A chitinase-secreting strain CH2 was one of 353 strains isolated from rhizosphere of eggplant. Based on 16S rDNA sequence alignment and several biochemical and physiological characteristics, the strain was identified to be of Bacillus cereus. On chitin–Ayers (CA) medium, the strain secreted chitinase. Evaluation of its activity, combined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), showed it to be a 15.0-KD chitinase. On glass slides, germination of the fungal spores was effectively suppressed by the bacterial suspension, supernatant from the suspension, and 0.005% solution of chitinase extracted from the strain CH2. The optimum pH for chitinase was 7.1 and optimum temperature was 40°C. At that temperature, high-level chitinolytic activity was retained for 10xa0days. In greenhouse experiments, suspension of the cells of the CH2 strain reduced the severity of Verticillium wilt on eggplant by 69.69%, its supernatant by 54.04%, and the enzyme diluted to 0.01% strength by 53.13% in 14xa0days. Strain CH2 and its chitinase have good commercial potential in controlling Verticillium wilt.

Composition and activity of rhizosphere microbial communities associated with healthy and diseased greenhouse tomatoes

AimsThe goal of this study was to investigate the structure and functional potential of microbial communities associated with healthy and diseased tomato rhizospheres.MethodsComposition changes in the bacterial communities inhabiting the rhizospheric soil and roots of tomato plants were detected using 454 pyrosequencing. Microbial functional diversity was investigated with BIOLOG technology.ResultsThere were significant shifts in the microbial composition of diseased samples compared with healthy samples, which had the highest bacterial diversity. The predominant phylum in both diseased and healthy samples was Proteobacteria, which accounted for 35.7–97.4xa0% of species. The class Gammaproteobacteria was more abundant in healthy than in diseased samples, while the Alphaproteobacteria and Betaproteobacteria were more abundant in diseased samples. The proportions of pathogenic Ralstonia solanacearum and Actinobacteria species were also elevated in diseased samples. The proportions of the various bacterial populations showed a similar trend both in rhizosphere soil and plant roots in diseased versus disease-free samples, indicating that pathogen infection altered the composition of bacterial communities in both plant and soil samples. In terms of microbial activity, functional diversity was suppressed in diseased soil samples. Soil enzyme activity, including urease, alkaline phosphatase and catalase activity, also declined.ConclusionsThis is the first report that provides evidence that R. solanacearum infection elicits shifts in the composition and functional potential of microbial communities in a continuous-cropping tomato operation.

Control of Tobacco mosaic virus by PopW as a Result of Induced Resistance in Tobacco Under Greenhouse and Field Conditions

In a previous study, we isolated a new harpin protein, PopW, from the bacterium Ralstonia solanacearum ZJ3721 that can induce a hypersensitive response in tobacco, Nicotiana tabacum, leaves. In the current study, we demonstrate that, in a greenhouse experiment, PopW induced tobacco-acquired resistance against the Tobacco mosaic virus (TMV) with a biocontrol efficacy of 80.9 to 97.4% at a concentration as low as 25 μg/ml in both PopW-treated and neighboring leaves. The resistance induced by PopW is systemic acquired resistance mediated by salicylic acid, which was certified by the development of resistance being accompanied by the expression of the pathogenesis-related-1 gene (PR1) 8 h after PopW was sprayed onto the tobacco leaves. In addition, hydrogen peroxide began to accumulate 10 h after PopW spraying, peaking at 24 h with a maximum concentration of 1.97 μM/g fresh weight. The activities of phenylalanine ammonia lyase (EC4.3.1.5), polyphenoloxidase (EC1.14.18.1), and peroxidase (EC1.11.1.7) also increased, peaking at different times in the PopW-treated tobacco leaves. PopW also reduced the level of TMV disease in field trials with a biocontrol efficacy of 45.2%. Furthermore, PopW both increased tobacco yield (by 30.4 more than in control plants) and improved tobacco foliar quality, with an increase of 50.2% in the number of first-class tobacco leaves from treated compared with untreated plants. All of these results indicate that the new harpin protein PopW has the potential to be an effective biocontrol agent against TMV in tobacco.

Effect of a rock dust amendment on disease severity of tomato bacterial wilt

Nutrients are important for growth and development of plants and microbes, and they are also important factors in plant disease control. The objective of this study was to evaluate the effect of a rock dust used as a fertilizer in maintaining health of soil and tomato plants under greenhouse conditions. Four treatments—including M (commercial organic fertilizer), A (rock dust soil amendment), Mxa0+xa0A (commercial organic fertilizerxa0+xa0rock dust soil amendment) and CK (blank control)—were examined for their effect on soil properties, soil enzymatic activity, plant growth and control efficacy against tomato bacterial wilt. Treatments A and Mxa0+xa0A were significantly better than other treatments in changing soil pH, increasing it from acidic (pH 5.13) to nearly neutral (pH 6.81 and 6.70, respectively). Enzymatic activities in soil were notably influenced by the different treatments—particularly treatment Mxa0+xa0A, which increased the activities of alkaline phosphatase, urease, catalase and sucrase to a greater extent in soil. There was no significant difference (Pxa0<xa00.05) in the effects of treatments A and Mxa0+xa0A on tomato plant height, stem diameter and biomass. The effect of the four treatments on the chlorophyll content and photosynthetic rate (in decreasing order) were Mxa0+xa0A, A, M and CK. The replicate greenhouse experiments showed that the control efficacies of treatments Mxa0+xa0A, A, and M against bacterial wilt were respectively 89.99, 81.11 and 8.89xa0% in first experiment and with the efficacies of 84.55, 74.36, and 13.49xa0% in the replicate; indicating that rock dust played a key role in the plant–soil interaction. The raised soil pH and Ca content were the key factors for the rock dust amendment controlling bacterial wilt under greenhouse conditions.

Effect of different levels of nitrogen on rhizosphere bacterial community structure in intensive monoculture of greenhouse lettuce.

Pyrosequencing-based analyses revealed significant effects among low (N50), medium (N80), and high (N100) fertilization on community composition involving a long-term monoculture of lettuce in a greenhouse in both summer and winter. The non-fertilized control (CK) treatment was characterized by a higher relative abundance of Actinobacteria, Acidobacteria, and Chloroflexi; however, the average abundance of Firmicutes typically increased in summer, and the relative abundance of Bacteroidetes increased in winter in the N-fertilized treatments. Principle component analysis showed that the distribution of the microbial community was separated by a N gradient with N80 and N100 in the same group in the summer samples, while CK and N50 were in the same group in the winter samples, with the other N-level treatments existing independently. Redundancy analysis revealed that available N, NO3−-N, and NH4+-N, were the main environmental factors affecting the distribution of the bacterial community. Correlation analysis showed that nitrogen affected the shifts of microbial communities by strongly driving the shifts of Firmicutes, Bacteroidetes, and Proteobacteria in summer samples, and Bacteroidetes, Actinobacteria, and Acidobacteria in winter samples. The study demonstrates a novel example of rhizosphere bacterial diversity and the main factors influencing rizosphere microbial community in continuous vegetable cropping within an intensive greenhouse ecosystem.

Effect of calcium nutrition on resistance of tomato against bacterial wilt induced by Ralstonia solanacearum

This study investigated the effect of calcium nutrition on tomato bacterial wilt caused by Ralstonia solanacearum and the regulation of resistance mechanisms. Plants cultured in nutrient solution with calcium concentrations of 0.5, 5.0, and 25.0xa0mM, were inoculated with R. solanacearum by the root dip method. Severity of disease development, Ca concentration in tomato root and shoot tissues, hydrogen peroxide (H2O2) concentration, peroxidase (POD, EC 1.11.1.7) and polyphenol oxidase (PPO, EC 1.10.3.2) in tomato leaves were analyzed. Disease severities of low, medium and high Ca treatments were 100xa0%, 77.1xa0% and 56.8xa0% respectively. Plant growth in high Ca treatment was significantly better than those in low Ca treatment in height, stem diameter and biomass. Tomato plants absorbed significantly more Ca in roots and shoots as the level of Ca in the nutrient solution increased. In addition, H2O2 level in high Ca treatment rose faster and reached a higher peak with 10.86xa0μMxa0gFW−1(31.32xa0% greater than medium Ca plants). The activities of POD and PPO also have a greater increase in high Ca treatment with 99.09xa0Uxa0gFW−1 and 107.24xa0Uxa0gFW−1 compared to 40.70xa0Uxa0gFW−1 and 77.45xa0Uxa0gFW−1 in low Ca treatment. A negative correlation was found between Ca concentration, level of H2O2, POD, PPO in tomato, and disease severity, indicating that they played an important role in resistance of tomato to this disease. These results suggested that Ca was involved in the regulation of H2O2 concentration, and activity of POD and PPO in tomato.

SCOPOLIN, A GLYCOSIDE FORM OF THE PHYTOALEXIN SCOPOLETIN, IS LIKELY INVOLVED IN THE RESISTANCE OF NICOTIANA ATTENUATA AGAINST ALTERNARIA ALTERNATA

Phenolic coumarins are secondary metabolites playing an important role in plant-environment interaction. Previously, we have shown that wild tobacco Nicotiana attenuata accumulates high amounts of the jasmonate (JA)-dependent phenolic coumarin, scopoletin, as a phytoalexin to defend itself against a necrotic fungal pathogen, Alternaria alternata (tobacco pathotype). Scopolin, a s-glycoside form of scopoletin, was strongly elicited and to a level even higher than that of scopoletin in host plants after A. alternata infection. However, it was not known whether scopolin functioned as a phytoalexin playing a role in the resistance or simply as a storage form of scopoletin. When supplied in PDA medium, scopolin exhibited a moderate but slightly weaker anti-fungal activity against A. alternata than that of scopoletin. In addition, A. alternata-elicited scopolin level was dramatically decreased in JA deficient plants. Thus, all the data suggest that scopolin is also a JA-dependent phytoalexin likely involved in the resistance of N. attenuata against A. alternata.

EFFECT OF BORON NUTRITION ON RESISTANCE RESPONSE OF TOMATO AGAINST BACTERIAL WILT CAUSED BY RALSTONIA SOLANACEARUM

This study investigated the effect of boron nutrient on tomato bacterial wilt caused by Ralstonia solanacearum and the regulation mechanisms. Plants, cultured in nutrient solution and treated with three concentrations of B (0.05, 0.50 and 2.50 mg l-1), were inoculated with R. solanacearum by the method of root dip. Severity of disease development, plant nutrient uptake, hydrogen peroxide (H2O2) activity, enzymes like peroxidase (POD, EC 1.11.1.7), polyphenol oxidase (PPO, EC 1.10.3.2) activities in tomato leaves were analyzed. Disease severity of low, medium and high B treatments were 95.2%, 72.6% and 63.4% respectively. There was no significant difference in plant dry weight, indicating no B toxic or deficiency phenomenon in all treatments. Tomato plants absorbed significantly more Ca and B with the level of B in the nutrient solution increased. In addition, H2O2 level in high B treatment rose faster and reached a higher peak with 11.94 μM gFW-1(96.7% greater than low B plants). The activities of POD and PPO also have a greater increase in high B treatment with 97.12 U gFW-1 and 94.00 U gFW-1 compared to 39.16 U gFW-1 and 70.51 U gFW-1 in low B treatment. These results suggested that the regulation mechanism of B was to increase the Ca and B concentration, improve the rate and the amount of H2O2 accumulation, and increase the activities of POD and PPO in tomato.