Plant and Soil

, Volume 237, Issue 1, pp 81–89 | Cite as

Suppression of the root rot–root knot disease complex by Pseudomonas aeruginosa in tomato: The influence of inoculum density, nematode populations, moisture and other plant-associated bacteria

  • Imran Ali SiddiquiEmail author
  • Syed Ehteshamul-Haque


The influence of different application rates of the plant growth-promoting rhizobacterium, Pseudomonas aeruginosa, population densities of the root-knot nematode, Meloidogyne javanica, moisture and other plant-associated bacteria in the suppression of root rot–root knot disease complex of tomato are described. The impact of these factors on bacterial rhizosphere and inner root and shoot establishment are also presented. The highest inoculum level of P. aeruginosa (7.4 × 108 cfu ml−1) in the presence of the lowest population density of M. javanica (500 J2/plant) caused the greatest reduction in gall formation due to M. javanica. The number of root–knot nematodes recovered from soil and roots treated with P. aeruginosa were also significantly reduced. Root infection caused by the soilborne root-infecting fungi Fusarium oxysporum, F. solani and Rhizoctonia solani was also effectively suppressed following application of P. aeruginosa. A P. aeruginosa-Bacillus subtilis treatment was the most effective in the suppression of root-rot disease complex with enhancement of plant growth. Biocontrol and growth promoting potential of the bacterium was enhanced when soil was kept at 50% or 75% moisture holding capacity, whereas a 25% MHC reduced bacterial efficacy. Rhizosphere population of P. aeruginosa declined drastically in P. aeruginosa-Bradyrhizobium japonicum treatments. Rhizosphere colonisation by P. aeruginosa seems to be governed by two factors: Initial inoculum size of the bacterium and severity of the root-knot disease. Endoroot and endoshoot colonisation of the bacterium was dependent on degree of root-colonisation by Fusarium oxysporum. An inoculum level 2.5 × 108 cfu/ml of P. aeruginosa was optimal for the enhancement of plant growth, whereas inoculum below this level reduced plant growth.

Pseudomonas aeruginosa endophyte root-knot nematode root-infecting fungi root-colonisation rhizosphere colonisation 


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Copyright information

© Kluwer Academic Publishers 2001

Authors and Affiliations

  1. 1.Soilborne Diseases Research Laboratory, Department of BotanyUniversity of KarachiKarachiPakistan

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