Variation and composition of bacterial populations in the rhizospheres of maize, wheat, and grass cultivars

Abstract

Differences in the size and composition of bacterial populations found in the rhizospheres of maize, wheat, and grass were compared. Significant differences in the fluorescent pseudomonad and "coryneform" groups were found among the cultivars of each plant species. Only between the two maize cultivars, reported to be resistant and susceptible to Fusarium species, and between the two grass lines, known to be resistant and susceptible to Dreschera poae, could significance be found in the total numbers of bacteria counted. In each case higher bacterial counts were recorded in the rhizospheres of cultivars susceptible to disease. No conclusion could be reached with regard to differences that occurred between the two cultivars of wheat that are known to differ in tolerance to pH. Although actinomycetes appeared to represent a high percentage of the total bacterial population in maize, insufficient data prevent further interpretation. Bacillus numbers do not differ with any significance betewen cultivars or even between cultivars and counts made in root-free soil. Both the Bacillus and fluorescent pseudomonad groups were found to be represented in lower numbers in the rhizosphere of all cultivars than either the actinomycetes or "coryneform" groups. The findings of this study correlate highly with previously published work in stressing the importance of the plant's influence on the bacteria in its own rhizosphere. As this may mean that a plant, given the right genetical configuration, can influence the development of a favourable rhizosphere flora, the mechanism involved in this relationship should be investigated.Key words: bacteria, disease resistance, pH, rhizosphere, selective stimulation.

Actinomycetes, promising tools to control plant diseases and to promote plant growth

“…Evidence indicates that actinomycetes are quantitatively and qualitatively important in the rhizosphere (Barakate et al 2002;Crawford et a/.1993;Doumbou et al 2001;Miller et al 1989Miller et al , 1990, where they may influence plant growth and protect plant roots against invasion by root pathogenic fungi (Lechevalier 1988). However root-microorganism interactions hâve been extensively studied only for the nitrogenfixing Frankia species (Sardi et al 1992) and a few species of the genus Streptomyces that are phytopathogens (Loria et al 1997).…”

The complete nucleotide sequence and environmental distribution of the cryptic, conjugative, broad-host-range plasmid pIPO2 isolated from bacteria of the wheat rhizosphere The GenBank accession number for the pIPO2T sequence reported in this paper is AJ297913.

“…For instance, Miller et al (1989) showed that fluorescent pseudomonads are avid responders to young roots of wheat and maize, enhancing their abundance. Upon plant ageing, these organisms were shown to decline.…”

Bulk and Rhizosphere Soil Bacterial Communities Studied by Denaturing Gradient Gel Electrophoresis: Plant-Dependent Enrichment and Seasonal Shifts Revealed

“…Most studies of the bacterial community structure of rhizospheres indicating a plant-dependent diversity were performed using cultivation-based techniques (12,23,25,28,30). The major problem of cultivation-based analysis is that only a small proportion of the bacterial populations can be recovered from the rhizosphere and soil by traditional cultivation techniques (1,46).…”