Host-Plant Selectivity of Rhizobacteria in a Crop/Weed Model System

Abstract

Belowground microorganisms are known to influence plants' performance by altering the soil environment. Plant pathogens such as cyanide-producing strains of the rhizobacterium Pseudomonas may show strong host-plant selectivity. We analyzed interactions between different host plants and Pseudomonas strains and tested if these can be linked to the cyanide sensitivity of host plants, the cyanide production of bacterial strains or the plant identity from which strains had been isolated. Eight strains (four cyanide producing) were isolated from roots of four weed species and then re-inoculated on the four weed and two additional crop species. Bacterial strain composition varied strongly among the four weed species. Although all six plant species showed different reductions in root growth when cyanide was artificially applied to seedlings, they were generally not negatively affected by inoculation with cyanide-producing bacterial strains. We found a highly significant plant species x bacterial strain interaction. Partitioning this interaction into contrasts showed that it was entirely due to a strongly negative effect of a bacterial strain (Pseudomonas kilonensis/brassicacearum, isolated from Galium mollugo) on Echinochloa crus-galli. This exotic weed may not have become adapted to the bacterial strain isolated from a native weed. Our findings suggest that host-specific rhizobacteria hold some promise as biological weed-control agents.

Volatile-Mediated Killing of Arabidopsis thaliana by Bacteria Is Mainly Due to Hydrogen Cyanide

“…1 and 3): 2 mol of chemically supplied HCN resulted in 6% of growth compared to the control, but when plants were grown in the presence of strains producing a similar quantity of HCN (PUPa3 and CV0), plant biomass was five times higher (30% of the control biomass). Similar observations were made in the field, where external application of HCN proved much more plant growth inhibitory than cyanogenesis by inoculated rhizosphere pseudomonad populations (53). In addition to the putative production of growth promoting volatiles by the bacterial strains, which could counteract the negative effect of HCN, the different timing dynamics of application is likely to account in great part for the differences observed in plant responses.…”

Janzen‐connell Effects Are Widespread and Strong Enough to Maintain Diversity in Grasslands

“…Pathogenic fungi are most often specifically examined in feedback studies and in some cases their effect has been directly demonstrated (Mills and Bever 1998, Packer and Clay 2000, Klironomos 2002. In a separate experiment, Zeller et al (2007) showed that the biomass of the species with the greatest negative soil feedback, Echinochloa crus-galli, is reduced by 90% when infected with a cyanide-producing Pseudomonas bacterial strain. In our study, we were unable to attribute the effect to soil fungi.…”

Diversity of Culturable Chitinolytic Bacteria from Rhizospheres of Agronomic Plants in Japan

“…However, several attempts to utilize only chitinolytic bacteria as biological control agents have failed (35,40). One reason for these failures is that both colonization and chitinase production by the bacteria in rhizospheres are affected by various factors including plant species, cultivars, the physiological condition of plants, soil type and indigenous microorganisms (16,19,33,45).…”