Agriculture Reference
In-Depth Information
gluconate dehydrogenase (
gad
) were deleted) acidified the environment and solu-
bilized mineral P. Furthermore, the formation of gluconic acid by CHA0
completely inhibited the production of PLT and partially hampered the synthesis
of DAPG. In the
gcd
mutant, which did not produce gluconic acid, the enhanced
production of antifungal compounds was associated with improved biocontrol
activity against take-all disease of wheat, caused by
Gaeumannomyces graminis
var.
tritici
. This study provided a new evidence for a close association of gluconic
acid metabolism with antifungal compound production and biocontrol activity in
P. fluorescens
CHA0 (de Werra et al.
2009
).
Pseudomonas fluorescens
strain Q8r1-
96, an aggressive colonizer of the wheat rhizosphere, in a study was found to
produce 1,850
Δ
gml
1
2,4-DAPG after 48 h of growth in King's B Medium,
while strain Q2-87V1 could produce only 19.4
μ
gml
1
metabolites under the
identical conditions. Rhizoplane levels of 2,4-DAPG after 4 days of Q8r1-96
colonization were 1,946, 1,650, and 2,767 ng g
1
for Buchanan, Finley, and Tara
wheat cultivars, respectively. Metabolite levels obtained for Q2-87V1 colonization
were 1,468, 366, and 80 ng g
1
on the respective cultivars. Thus, strain Q8r1-96
produced significantly more 2,4-DAPG than Q2-87V1 on Tara and Finley roots,
whereas both strains produced similar amounts of the metabolites on Buchanan
roots. In greenhouse experiments, take-all damage was reduced only on Tara roots
inoculated with Q8r1-96. Moreover, in a recent study, bacterial strain,
Pseudomo-
nas brassicacearum
J12, isolated from the rhizosphere soil of tomato plants
strongly inhibited the growth of phytopathogenic bacteria
Ralstonia solanacearum
.
J12 could produce 2,4-diacetylphloroglucinol (2,4-DAPG), HCN, siderophore(s),
and protease. The maximum growth and antagonistic activity were recorded at
30
C and pH 8. Strain J12 significantly suppressed tomato bacteria wilt by 45.5 %
in the greenhouse experiment. The main antimicrobial compound of J12 was
identified as 2,4-diacetylphloroglucinol (2,4-DAPG) by HPLC-ESI-MS analysis
(Zhou et al.
2012
). One problem with depending too much on antibiotic-producing
bacteria as biocontrol agents is, however, that with the increased use of these
bacterial strains, some phytopathogens may also develop resistance to specific
antibiotics in a manner similar to those exhibited for chemically synthesized
antibacterial drugs. To obviate this, it is suggested that the HCN positive biocontrol
agents should be utilized along with antibiotics producing bacterial strains in order
to suppress the pathogens and to avoid emergence of antibiotic resistance among
bacterial species. This approach seems more credible because while HCN may not
have a strong biocontrol activity by itself, it may act synergistically with bacterially
encoded antibiotics.
μ
Lytic Enzyme
Lytic enzymes such as chitinase, pectinases, and cellulases secreted by a variety of
microorganisms including PS organisms disrupt the functionality of pathogens by
hydrolyzing chitin, pectins, and cellulose, respectively, and thus play a pivotal role
