Suppression of Meloidogyne incognita by Pseudomonas fluorescens strain CHA0 and its genetically-modified derivatives: II. The influence of sodium chloride


  • I. A. Siddiqui
  • S. S. Shaukat


Culture filtrates of the Pseudomonas /luorescens strain CHAO and its diacetylphloroglucinol (DAPG)-overproducing derivative CHAO/pME3424 inhibited egg hatch and induced mortality of Meloidogyne incognita juveniles in vitro. Nutrient yeast extract broth medium amended with various concentrations of NaCl influenced antagonistic activity of the two strains of the bacteria; their inhibitory effect was enhanced when the growth medium was supplemented with 0.4 or 0.8 M NaCl but a concentration greater than 0.8 M NaCl slightly reduced bacterial activity against the nematodes. Strain CHA89, a DAPG-negative mutant, and strain CHAn, a hydrogen cyanide-negative mutant of the strain CHAO, failed to induce such inhibitory effects on eggs and juveniles of M. incognita. Application of P. /luorescens strain CHAO, CHAO/pME3424 or CHAn to a non-sterilized sandy loam soil reduced M. incognita population densities in roots and subsequent root-knot development on tomato whereas strain CHA89 did not. Soil amended with NaCl enhanced the efficacy of strains CHAO and CHA/pME3424 against root-knot nematode on tomato but not strain CHAn. A 0.8 M NaCl concentration was optimal for the biocontrol effectiveness of the bacteria. Neither wild type strain CHAO nor its transgenic derivatives influenced tomato root growth in soil with or without NaCl. The bacterial strains did not differ markedly in their rhizosphere colonization pattern.