Rhizobacteria of Cotton and Their Repression of Seedling Disease Pathogens

Abstract

During the 1983 field season, the rhizobacteria (including organisms from rhizosphere soil and the root rhizoplane) of cotton plants at one location in Mississippi were inventoried at different plant growth stages. Isolates (1,000) were identified to the genus level and characterized for repression of Pythium ultimum and Rhizoctonia solani. Cotton seedlings were initially colonized by bacteria of many different genera, and populations quickly reached 10 8 CFU/g of root tissue. As the season progressed, the bacterial populations declined as root mass increased and the roots became more woodlike in consistency. Fluorescent pseudomonads were the most numerous gram-negative rhizobacterial isolates of those that were randomly collected and identified, and they provided the largest number of isolates with fungal repressive activity. Several other gram-negative bacterial genera were recovered throughout the growing season, and some gram-positive bacteria were also isolated routinely, but at lower numbers. There was no correlation between the proportion of rhizobacterial isolates that possessed fungal repressive activity and the plant growth stage from which the isolates were obtained. Approximately twice as many bacterial isolates demonstrated fungal repression in the agar assay compared with the inplanta assay, and isolates were found more frequently with fungal repressive activity against P. ultimum than against R. solai.

Humus bacteria of Norway spruce stands: plant growth promoting properties and birch, red fescue and alder colonizing capacity

“…The antifungal activity of rhizobacteria has been ascribed to these bacterial groups by many authors (e.g. [7,43,44]). Of the Streptomyces isolates from spruce humus 46% suppressed one or more of the indicator fungi, similar to the frequency reported previously for rhizosphere and non-rhizosphere isolates [7,44].…”

Humus bacteria of Norway spruce stands: plant growth promoting properties and birch, red fescue and alder colonizing capacity

“…The antifungal activity of rhizobacteria has been ascribed to these bacterial groups by many authors (e.g. [7,43,44]). Of the Streptomyces isolates from spruce humus 46% suppressed one or more of the indicator fungi, similar to the frequency reported previously for rhizosphere and non‐rhizosphere isolates [7,44].…”

“…The humus bacteria may thus have natural potential for attenuating autochthonous fungi as biological control agents in spruce nurseries. Several reports indicate a correlation between in vitro growth inhibition and biocontrol [45], but many other studies found no advantage in screening the strains in vitro [43–45]. Broadbent et al [46] noted that strains nonantagonistic in plate assays were generally inactive in soil also.…”

Influence of some culture media on antifungal activity of Pseudomonas fluorescens UTPF61 against the Sclerotinia sclerotiorum

“…Plates were incubated at 20°C for five days and examined for the evidence if the growth of the fungus was inhibited by the bacteria. A positive response was any visible zone of inhibition around the fungus, regardless of the size of the zone (Hagedorn et al, 1989). All the 47 bacterial isolates were tested in three independent replicates.…”