Interactions between fluorescent pseudomonads and VA mycorrhizal fungi



Cucumber seeds were treated with rifampin-resistant derivatives of Pseudomonas putida (A12, NI or R-20) or R-20 or P. fluorescens (2–79 or 3871) and planted in soils with and without added inoculum of the VA mycorrhizal fungi Glomus intraradices Schenck & Smith or G. etunicatum Becker & Gerdemann. Populations of Pseudomonas spp. in the combined rhizosphere-rhizoplane soil were determined at 1–9 weeks after planting by dilution plating on a selective medium. At 1–3 weeks, the populations of all strains except R–20 were 1.5 to 7 times lower in the rhizosphere of cucumber roots colonized by G. intraradices, when compared to nonmycorrhizal plants. However, this effect was less consistent in 3- to 9-week-old plants. No significant difference was detected in populations of Pseudomonas strains between roots colonized by G. etunicatum and nonmycorrhizal roots. Strains 3871 and 2-79, which are antibiotic producers, delayed the germination of G. etunicatum spores in raw soil, but by seven days no significant differences in frequency of germination were detected. None of the fluorescent Pseudomonas strains affected the colonization of cucumber roots by G. etunicatum, as determined by measurements of mycorrhizal inoculum density root colonization relationships.