Growth promotion and inhibition by antibiotic-producing fluorescent pseudomonads on citrus roots

• Published in: Plant and soil 1984-02, Vol.77 (1), p.103-113
• Main Authors: GARDNER, JOHN M., CHANDLER, JUAN L., FELDMAN, ALBERT W.
• Format: Article
• Language: English
• Subjects: Agrology; Antibiotics; Bacteria; Bacterial plant pathogens; Biological and medical sciences; Citrus jambhiri; Citrus sinensis; Fundamental and applied biological sciences. Psychology; Groves; Orchard soils; Phytopathology. Animal pests. Plant and forest protection; Plant roots; Plants; Pseudomonas fluorescens; Pseudomonas putida; rats; Seedlings; Siderophores; Soil microorganisms; Systematics. Structure, properties and multiplication. Genetics
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/bf02182816

Forty-three strains of feeder root colonizing fluorescent pseudomonads from rough lemon (Citrus jambhiri Lush.) roots were examined for effects on rough lemon and sweet orange (Citrus sinensis Osbeck) seedlings. Plants inoculated with a single bacterial soil-drench had, after 10 months, a range of stimulatory (to 116%) and inhibitory effects (to 52%). Stimulatory bacteria particularly increased growth of root systems. Cultivar-specific inhibition and stimulation was evident in inoculations of rough lemon and sweet orange seedlings. Populations of fluorescent rhizobacteria on inoculated and noninoculated, as well as on stimulated and nonstimulated seedlings, did not differ significantly (10.8 × 10⁶ to 30.3 × 10⁶ CFU/g root). Populations of fluorescent rhizobacteria on seedlings were higher than populations on feeder roots from grove trees (2.8 to 5.7 × 10⁶ CFU/g). Ninety-four and 81% of 251 fluorescent strains produced antibiotics against the fungus Geotrichum candidum and the bacterium Erwinia stewartii, respectively. Antibiotic activities of 90% of the antibiotic producing strains were repressed by Fe³⁺, indicating siderophore production. In comparison, only 9.6 and 15% of 94 randomly selected nonfluorescent Pseudomonas strains were antibiotic producers. Differences between stimulatory and inhibitory or neutral bacteria were not apparent from antibiosis tests. On the basis of physiological tests, Pseudomonas putida was the most abundant (> 62%) pseudomonad species on rough lemon roots. Growth stimulating strains appeared to be in both P. putida and P. fluorescens groups. Few P. aeruginosa strains were identified on citrus roots.