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.