Improvement of Pseudomonas fluorescens CHA0 biocontrol activity against root-knot nematode by the addition of ammonium molybdate

Abstract

Aims: To improve the efficacy of Pseudomonas fluorescens CHA0 and its genetically modified (GM) derivatives by adding ammonium molybdate to control Meloidogyne javanica, the root-knot nematode in mungbean. Methods and Results: Culture filtrate of P. fluorescens CHA0 and its GM derivative (antibiotic overproducing strain CHA0/pME3424 and antibiotic-deficient CHA89) obtained from nutrient broth yeast extract medium amended with 1, 2 or 4 mM M of ammonium molybdate (NH 4 -Mo) caused substantial mortality of M. javanica juveniles in vitro. Pseudomonas fluorescens CHA0 or CHA0/pME3424 applied in conjunction with NH 4 -Mo caused greater reduction of nematode penetration in mungbean roots compared with the bacterial application alone. Ammonium molybdate at 4 mg kg )1 of soil along with CHA0 also enhanced plant height while shoot weight remained unaffected. Either used alone or in conjunction with NH 4 -Mo, strain CHA89 did not reduce nematode invasion compared with the controls. Bacterial strains did not differ significantly in their colonization potential in the mungbean rhizosphere. Efficacy of the biocontrol bacteria to control root-knot nematode was accentuated when soil was treated with NH 4 -Mo and zinc (both at 1 mg kg )1 of soil). Conclusion: The addition of ammonium molybdate enhances the production of nematicidal compounds by P. fluorescens in vitro and improves bacterial efficacy against root-knot nematode under glasshouse conditions. Significance and Impact of the Study: Application of minerals such as ammonium molybdate is appealing because they are cheap and can easily be applied under field conditions to improve biocontrol potential of the bacterial inoculants. They also significantly reduce the amount of biocontrol inoculant biomass required to achieve root-knot disease control, with a consequent reduction in cost.

Use of Bromodeoxyuridine Immunocapture To Identify Active Bacteria Associated with Arbuscular Mycorrhizal Hyphae

“…were found, which is consistent with previous studies in which primarily gram-positive, rod-shaped bacteria associated with AM (8,43) and ectomycorrhizal (47) (22,36,53,58,59) or BrdU (57) into their genomes. It has previously been shown by using other approaches that gram-negative bacteria, such as pseudomonads, are predominantly active in rhizospheres or upon nutrient addition in soil (10,26), and thus they often behave as opportunistic r strategists (35). By contrast, the gram-positive bacteria in this study were active in bulk soil fractions containing mycorrhizae, typically a low-nutrient ecosystem that commonly favors k strategists.…”

Biological control of rice root-knot nematode,Meloidogyne graminicolathrough mixture ofPseudomonas fluorescensstrains

“…The application P. fluorescens P523 to beet seeds reduced 68Á75% of root penetration by sugar beet cyst nematode, Heterodera schachtii (Oostendorp and Sikora 1990). Efficacy of P. fluorescens strain CHA0 against root-knot nematodes, Meloidogyne javanica (Treub 1885) Chitwood, 1949 and Meloidogyne incognita (Kofoid & White 1919) Chitwood, 1949 was reported in tomato (Hamid, Siddiqui, and Shaukat 2003;Siddiqui and Shaukat 2003). Isolates of P. fluorescens were also reported to be effective for reducing the population of root-knot nematode, Meloidogyne incognita in medicinal coleus (Seenivasan and Devrajan 2008) and potato cyst nematode, Globodera rostochiensis in potato (Seenivasan, Devrajan, and Selvaraj 2007).…”

New Approaches for Bioaugmentation as a Remediation Technology

“…147,175 Other agricultural applications of bioaugmentation include inoculation of plant seeds with plantgrowth-promoting microorganisms or with plant-protecting microorganisms that are antagonistic to plant pathogens. 15,88,157 Inoculation is also used to transform agricultural products into more useful forms such as the generation of silage from forages. 227 More recently, bioaugmentation has been applied in attempts to remediate numerous environmental problems.…”