Culture-Based Assessment of Microbial Communities in Soil Suppressive to Potato Common Scab

Abstract

A field in East Lansing, MI, showed a decline of potato common scab compared with an adjacent potato field. To confirm that the decline was due to biological factors, the soil was assayed. In the greenhouse, putative common-scab-suppressive soil (SS) was either treated with various temperatures or mixed with autoclaved SS at various ratios. Pathogenic Streptomyces scabies was incorporated into the treated soil at 106 CFU/cm3 of soil, followed by planting of either potato or radish. Disease severity was negatively correlated with the percentage of SS in the mixture and positively correlated with temperature above 60°C. The soil was screened for four groups of potential antagonists (general bacteria, streptomycetes, fluorescent pseudomonads, and bacilli) pairing in culture with S. scabies. The frequency of antagonistic bacteria in SS was higher than common-scab-conducive soil (CS) in all four groups but only pseudomonads and streptomycetes were significantly higher. The population of pathogenic Streptomyces spp. in the rhizosphere of CS was significantly higher than SS. Dilution plating of CS and SS samples showed no clear trends or differences in populations of total fungi, total bacteria, streptomycetes, fluorescent pseudomonads, and bacilli but terminal restriction fragment polymorphism analysis revealed two distinct microbial communities were present in SS and CS.

Streptomyces species associated with common scab lesions of potatoes in South Africa

“…Although the tuber slice assay is not sensitive enough for virulence testing, it is an efficient screening method and correlates well with pot trials for pathogenicity evaluation (Park et al 2003;Hao et al 2009;Meng et al 2012). …”

Synergists and antagonists in the rhizosphere modulate microbial communities and growth of Quercus robur L.

“…They frequently inhabit the rhizospheres of plants, where they may influence plant growth and fungal-plant symbiosis (Frey-Klett et al, 2011). In addition, several species like Streptomyces act as biocontrol agents producing an extraordinary diversity of secondary metabolites capable of providing protection against phytopathogens, predominantly nematodes (Zuckerman et al, 1989;Nair et al, 1995;Ruanpanun et al, 2011;Meng et al, 2012), bacteria (Postma et al, 2008) and fungi (Dicklow et al, 1993). In fact, Streptomyces are believed to be implicated in natural soil suppressiveness (Meng et al, 2012).…”

“…In addition, several species like Streptomyces act as biocontrol agents producing an extraordinary diversity of secondary metabolites capable of providing protection against phytopathogens, predominantly nematodes (Zuckerman et al, 1989;Nair et al, 1995;Ruanpanun et al, 2011;Meng et al, 2012), bacteria (Postma et al, 2008) and fungi (Dicklow et al, 1993). In fact, Streptomyces are believed to be implicated in natural soil suppressiveness (Meng et al, 2012). Other direct antagonistic effects such as competition for nutrients, occupation of diverse ecological niches and infection sites could be involved in the biocontrol activity of these bacteria (Siddiqui and Mahmood, 1999;Kinkel et al, 2012).…”

Effect of Antibiotics on Indole-3-Acetic Acid Production by Klebsiella Pneumoniae, Bacillus Subtilis and Bacillus Amyloliquefaciens

“…One of the direct mechanism of plant growth promotion is through the release of phytohormones,likeindole acetic acid (IAA).Which regulate various metabolic processes during plant growth and development.Indirect mechanisms of plant growth promotion includes antibiotic production (Glick et al, 1999).Bacillus amyloliquefacienshas been recognized as a good plant growth promoter and root colonizer (Fan et al, 2011). Antimicrobial activity of Bacillus amyloliquefaciens has been well documented (Meng et al, 2012). Bacillus amyloliquefaciens is a closely related species to B. subtilis production of antibiotics are believed to be major contributors to disease suppression also (Stapleton and Devay, 1984 of Klebsiella pneumonia has also been well documented .The present study is aimed to evaluate the effect of six antibiotics on IAA production under in vitro conditions by the six strains.…”