Plant Species, Host Age and Host Genotype Effects on Meloidogyne incognita Biocontrol by Pseudomonas fluorescens Strain CHA0 and its Genetically-Modified Derivatives

Pseudomonas fluorescens strain CHA0 and its antibiotic overproducing derivative CHA0/pME3424 repeatedly reduced Meloidogyne incognita galling on tomato, brinjal, mungbean and soya bean roots but not in chilli. An antibiotic‐deficient derivative, CHA89, did not reduce nematode invasion in any of the plant species tested. When plant species were compared, bacterial inoculants afforded better protection to tomato, mungbean and soya bean roots against root‐knot nematodes than to brinjal and chilli. Antibiotic overproducing strain CHA0/pME3424 markedly reduced fresh shoot weights of chilli and mungbean while antibiotic‐deficient strain CHA89 enhanced fresh shoot weights of mungbean. While strains CHA0 had no significant impact on fresh root weights of any of the plant species, strain CHA0/pME3424 consistently reduced fresh root weights of brinjal and mungbean. In none of the plant species the bacterial strains had an influence on protein contents of the leaves. Regardless of the plant species, the three bacterial strains did not differ markedly in their rhizosphere colonization pattern. However, colonization was highest in brinjal rhizosphere and lowest in the mungbean rhizosphere. A slight host genotype effect on the biocontrol performance of the bacterial inoculants was also detected at cultivar level. When five soya bean cultivars were compared, biocontrol bacteria exhibited best suppression of the root‐knot nematode in cv. Ajmeri. Antibiotic overproducing strain CHA0/pME3424 substantially reduced fresh shoot weights of the soya bean cultivars Centuray 84 and NARC‐I while strain CHA89 enhanced shoot weights of the cultivars Ajmeri, William‐82 and NARC‐II. Wild type strain CHA0 had no significant impact on fresh shoot weights of any of the soya bean cultivars. Strain CHA0/pME3424 reduced fresh weights of root of Century 84, NARC‐I and NARC‐II while strain CHA89 increased root weights. Bacterial rhizosphere colonization was highest in variety NARC‐I and lowest in variety Ajmeri. Plant age had a significant impact on the biocontrol performance of bacterial inoculants against nematodes. The biocontrol effect of all bacterial strains was more prominent during early growth stage (7 days after nematode inoculation). A strong negative correlation between bacterial rhizosphere colonization and nematode invasion in soya bean roots was observed.