Elicitor Of Systemic Resistance Research Articles

Biocontrol of vascular streak dieback (Ceratobasidium theobromae) on cacao (Theobroma cacao) through induced systemic resistance and direct antagonism

ABSTRACTVascular streak dieback (VSD), caused by Ceratobasidium theobromae (P.H.B. Talbot & Keane), has a considerable impact on cacao (Theobroma cacao L.) production in Southeast Asia. Two biocontrol experiments were set up to explore alternatives to ineffective chemical control of VSD. The effects on VSD development of (i) Trichoderma harzianum, superficially applied to leaves of mature cacao plants, and (ii) an inoculation with fungal (Trichoderma asperellum) and bacterial (Bacillus sp., Pseudomonas sp. and Enterobacter spp.) elicitors of systemic resistance in young cacao plants, were tested. After three months, cacao leaves treated with T. harzianum exhibited a significantly (p < .05) lower disease score compared to the untreated control leaves, with no significant differences or interaction effects between three cacao clones tested. Six months after inoculation of cacao seedlings with elicitors, a significant (p < .05) effect on the number of VSD-affected leaves per plant was evidenced on seedlings treated with Bacillus sp. and Enterobacter spp. After transplanting to the field (8 months after inoculation), both number of VSD-affected leaves per plant and number of VSD-affected leaves per branch per plant were significantly (p < .05) lower as compared to control plants following inoculation by all bacterial elicitors tested, with no significant differences in the VSD controlling effect observed between the different bacterial elicitors tested. T. asperellum did not show potential as an elicitor of systemic resistance in our experiment. More research is needed on the lasting effect of biocontrol treatments, as well as on their economic and ecological sustainability.

Screening of plant growth-promoting rhizobacteria as elicitor of systemic resistance against gray leaf spot disease in pepper

This study investigated the effects of plant growth-promoting rhizobacteria (PGPR) isolated from Dokdo Island for growth promotion of pepper and biological control activity against a gray leaf spot disease pathogen, Stemphylium lycopersici. Screening of PGPR was carried out in the rhizosphere of wild plant Elymus tsukushiensis from Dokdo. Rhizobacterial isolates were partially identified based on analysis of 16S rDNA sequences. Phylogenetic analysis was performed using sequences of bacterial isolates for comparative purposes. To select PGPR, all bacterial isolates were tested for phosphate solubilization, production of indole-acetic acid (IAA), and siderophores. Isolates positive for all three characteristics were selected and tested for growth promotion of pepper as well as potential biological control of S. lycopercisi. All selected isolates were able to enhance plant growth with Kluyvera cryocrescens KUDC1771 showing the highest plant growth promoting activity. Among selected isolates, four significantly decreased gray leaf spot disease severity with Brevibacterium iodinum KUDC1716 providing the highest disease suppression. Moreover, KUDC1716 enhanced expression of pathogenesis-related (PR) protein genes including CaPR4 and CaChi2 in the absence of pathogen. These results suggest that B. iodinum induce defense response against S. lycopersici and can be used as a potential agent for biological control.

Harzianolide, a novel plant growth regulator and systemic resistance elicitor from Trichoderma harzianum

A detailed understanding of the effect of natural products on plant growth and protection will underpin new product development for plant production. The isolation and characterization of a known secondary metabolite named harzianolide from Trichoderma harzianum strain SQR-T037 were described, and the bioactivity of the purified compound as well as the crude metabolite extract in plant growth promotion and systemic resistance induction was investigated in this study. The results showed that harzianolide significantly promoted tomato seedling growth by up to 2.5-fold (dry weight) at a concentration of 0.1 ppm compared with the control. The result of root scan suggested that Trichoderma secondary metabolites may influence the early stages of plant growth through better root development for the enhancement of root length and tips. Both of the purified harzianolide and crude metabolite extract increased the activity of some defense-related enzymes to response to oxidative stress. Examination of six defense-related gene expression by real-time reverse transcription-PCR analysis revealed that harzianolide induces the expression of genes involved in the salicylic acid (PR1 and GLU) and jasmonate/ethylene (JERF3) signaling pathways while crude metabolite extract inhibited some gene expression (CHI-II and PGIP) related to basal defense in tomato plants. Further experiment showed that a subsequent challenge of harzianolide-pretreated plants with the pathogen Sclerotinia sclerotiorum resulted in higher systemic resistance by the reduction of lesion size. These results indicate that secondary metabolites of Trichoderma spp., like harzianolide, may play a novel role in both plant growth regulation and plant defense responses.

Induced defense responses in tomato against bacterial spot by proteins synthesized by endophytic bacteria

Some endophytes can synthesize molecules that elicit the induction of plant resistance to infection by pathogens. The objective of this study was to demonstrate that protein fractions 42 and 75 from Bacillus amyloliquefaciens and Bacillus pumilus were capable of acting as elicitors of induced resistance in tomato plants against Xanthomonas vesicatoria, following partial resolution by gel-filtration chromatography. Tomato plants sprayed with protein fractions 42 and 75 reduced, respectively, 63.5 and 56.6% of bacterial spot, compared with control plants. Additionally, these fractions promoted the increase of peroxidase (POX) and polyphenol oxidase (PPO) enzyme activities in treated plants. In SDS-PAGE stained with silver nitrate, protein fractions 42 and 75 appeared as simple bands with estimated molecular mass of 28 and 43 kDa, respectively. We report the partial characterization of two macromolecules synthesized by endophytic bacteria that act as elicitors of systemic resistance in tomato against X. vesicatoria.

Macromolecules Released by a Plant Growth‐promoting Rhizobacterium as Elicitors of Systemic Resistance in Tomato to Bacterial and Fungal Pathogens

AbstractOne of 500 rhizobacteria isolated from soil, rhizosphere and rhizoplane of healthy tomato plants was previously selected in laboratory, greenhouse and field tests as a good inducer of systemic resistance. This plant growth‐promoting rhizobacterium (PGPR) was identified as Bacillus cereus by fatty‐acid analysis. Bacillus cereus bacterial cells were removed from liquid culture by centrifugation and the supernatant repeatedly dialyzed (cut‐off = 12 000 daltons) against distilled water. Dialysates applied to roots protected tomato plants against leaf fungal and bacterial pathogens, evidence that macromolecules synthesized by the PGPR and released into the environment act as elicitors of systemic resistance.

Riboflavin Induces Disease Resistance in Plants by Activating a Novel Signal Transduction Pathway

ABSTRACT The role of riboflavin as an elicitor of systemic resistance and an activator of a novel signaling process in plants was demonstrated. Following treatment with riboflavin, Arabidopsis thaliana developed systemic resistance to Peronospora parasitica and Pseudomonas syringae pv. Tomato, and tobacco developed systemic resistance to Tobacco mosaic virus (TMV) and Alternaria alternata. Riboflavin, at concentrations necessary for resistance induction, did not cause cell death in plants or directly affect growth of the culturable pathogens. Riboflavin induced expression of pathogenesis-related (PR) genes in the plants, suggesting its ability to trigger a signal transduction pathway that leads to systemic resistance. Both the protein kinase inhibitor K252a and mutation in the NIM1/NPR1 gene which controls transcription of defense genes, impaired responsiveness to riboflavin. In contrast, riboflavin induced resistance and PR gene expression in NahG plants, which fail to accumulate salicylic acid (SA). Thus, riboflavin-induced resistance requires protein kinase signaling mechanisms and a functional NIM1/NPR1 gene, but not accumulation of SA. Riboflavin is an elicitor of systemic resistance, and it triggers resistance signal transduction in a distinct manner.