Effect of Antibiosis on Antagonist Dose-Plant Disease Response Relationships for the Biological Control of Crown Gall of Tomato and Cherry

Abstract

The crown gall pathosystem was used to evaluate a model that describes the dose-response relationship between biological control agents and plant pathogens. The model predicts that this relationship can become asymptotic, such that increased antagonist doses cannot compensate for deficiencies in disease suppression. Wounded roots of tomato (Lycopersicon esculentum) and cherry (Prunus mahaleb) plants were dipped into different concentrations of the biological control organism Agrobacterium radiobacter strain K84 prior to inoculation with the pathogen A. tumefaciens. Pathogen strains sensitive or resistant to the antibiotic agrocin 84 were used, and for tomato experiments, a derivative of A. radiobacter strain K84 that does not produce agrocin 84 also was included as an experimental treatment. As predicted by the dose-response model, the amount of disease suppression per unit of antagonist decreased with increasing antagonist dose and became asymptotic at high antagonist densities. Control of crown gall of tomato was nearly complete with the combination of A. radiobacter K84 and an agrocin 84-sensitive strain of A. tumefaciens. Pathogen resistance to agrocin 84 or lack of agrocin 84 production by A. radiobacter resulted in antagonist dose-crown gall incidence relationships that were apparently asymptotic at levels of control significantly less than 100%. For field-grown cherry, similar dose-response relationships were observed with higher asymptotic levels of disease suppression obtained when trees were inoculated with an agrocin 84-sensitive A. tumefaciens strain compared with an agrocin 84-resistant pathogen strain. The differences among bacterial strain combinations in the magnitude of the asymptote defined by the dose-response relationships suggest that A. radiobacter impacts a smaller proportion of the pathogen population when the activity of agrocin 84 is muted.

Plant-Growth Promotion and Biocontrol Properties of Three Streptomyces spp. Isolates to Control Bacterial Rice Pathogens

“…Field experiments are necessary to further verify the effects on rice plants under natural growth conditions. Further studies will allow establishing the relationship between application of strain Streptomyces A20 and plant disease suppression, as well as the spatial-temporal dynamics of the pathogens and antagonists in soil (Johnson and Dileone, 1999).…”

Initialin vitroevaluations of the antibacterial activities of glucosinolate enzymatic hydrolysis products against plant pathogenic bacteria

“…In recent years the research for new techniques and new strategies for plant disease management led to the development of studies with plant pathogen antagonists (Johnson and Dileone 1999; Bashan and de‐Bashan 2002; Aysan et al. 2003).…”

“…In recent years the research for new techniques and new strategies for plant disease management led to the development of studies with plant pathogen antagonists (Johnson and Dileone 1999;Bashan and de-Bashan 2002;Aysan et al 2003). Increasing attention is given to glucosinolates and their enzymatic derivatives, because of their control activity against several plant pathogens, insects and nematodes (O'Callaghan et al 2000;Buskov et al 2002;Serra et al 2002).…”

Induced Systemic Resistance and the Rhizosphere Microbiome

“…To effectively elicit ISR high population densities of a specific biocontrol strain are introduced into the soil or rhizosphere, usually around 10 7 colony forming units (cfu) per gram of root, see for example Van Pelt et al (2008). Dose response studies for biological control agents revealed that high populations are needed for effective control of diseases (Bull et al, 1991; Johnson and DiLeone, 1999; Montesinos and Bonaterra, 1996; Raaijmakers and Weller, 1998). Typically bacterial population densities of at least 10 5 cfu per gram of root are required for control of diseases by fluorescent pseudomonads, either mediated by antibiosis (Raaijmakers and Weller, 1998), or by ISR (Raaijmakers et al, 1995).…”