Abstract:
Plant growth-promoting rhizobacteria (PGPR) are bacteria that colonize the
rhizosphere and/or roots in the presence of other soil microflora and have growth
promotion activity and/or biocontrol activity. Plant growth-promoting rhizobacteria can
be integrated into modern agriculture. The main objective of the current study was to
identify strains of PGPR for use as biocontrol agents against Meloidogyne incognita
(Kofoid & White, 1919) Chitwood, 1949 on soybean and to study the mechanisms of
control involved.
A seedling bioassay was used to screen PGPR (from the PGPR collection of the
University of Pretoria) for biocontrol of M. incognita on soybean seedlings.
Lysinibacillus sphaericus strain T19, Paenibacillus alvei strain T22 and Pseudomonas
fluorescens strain N04 reduced the number of M. incognita galls per plant by 30 % or
more during two seedling bioassays.
The selected strains were tested in greenhouse trials. Strain T19 proved to be the
most consistent-performing biocontrol agent among the selected strains. The strain
(applied as a Perlite powder seed treatment) reduced the number of M. incognita egg
masses on roots of soybean plants significantly. Strains T19 and T22, applied as
Perlite powder seed treatments, increased dry shoot mass and leaf area of soybean
plants in experiments to test plant growth enhancement.
The ability of selected rhizobacteria to produce nematode-suppressive metabolites
was assessed with in vitro assays. Strains T19, T22 and N04 appear to produce
metabolites (in broth culture) that reduce motility as well as hatching of M. incognita
second-stage juveniles. A split-root assay was attempted. Strain T22 induced
resistance against M. incognita in soybean in one of two split-root experiments.
Lysinibacillus sphaericus strain T19 may be useful for control of M. incognita on
soybean within an integrated pest management system. Strains T19 and T22 may also
be useful as biofertilisers and could allow application of fertilisers at reduced rates.
