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in direct suppression of plant pathogens (Chernin and Chet
2002
; Kamensky
et al.
2003
; Ovadis et al.
2004
; Kim et al.
2008
). The extracellular secretion of
hydrolytic enzymes, for example, chitinase, is considered distinctly crucial in
disease management strategies. For instance,
S. plymuthica
C48 through the pro-
duction of chitinase has been found to inhibit spore germination and germ-tube
elongation in fungal pathogen,
Botrytis cinerea
(Frankowski et al.
2001
). Likewise,
the PS bacterium
Serratia marcescens
(Wani et al.
2005
) has shown antagonist
activity against
Sclerotium rolfsii
(Ordentlich et al.
1988
), while
Paenibacillus
sp. strain 300 and actinomycetes
Streptomyces
sp. strain 385 suppressed
F. oxysporum
f. sp
cucumerinum
. Extracellular chitinase and laminarinase synthe-
sized by
Pseudomonas stutzeri
digested and lysed mycelia of
F. solani
(Lim
et al.
1991
). In yet other example, secretion of
-1,3-glucanases and chitinases
and induction of host resistance by
P. guilliermondii
M8 played a major role in the
biocontrol of
P. guilliermondii
M8 against
B. cinerea
(Zhang et al.
2011
). The
1,3-glucanase synthesized by
Paenibacillus
sp. strain 300 and
Streptomyces
sp. strain 385 lysed fungal cell walls of
F. oxysporum
fsp.
cucumerinum
(Singh
et al.
1999
). Similar degradation of cell wall of
R. solani
,
S. rolfsii
, and
Pythium
ultimum
by 1,3-glucanase of
B. cepacia
is reported (Fridlender et al.
1993
). In other
investigation, the PS bacterial strains produced protease and exhibited a broad-
spectrum antifungal activity against phytopathogenic fungi. Also, when tested in
PCR using the gene-specific primers, PS strain BFPB9 showed the presence of
hcnBC genes that encode HCN. On the basis of phenotypic traits, 16S rRNA
sequence homology, and subsequent phylogenetic analysis, PS strains BFPB9,
FP12, and FP13 were identified as
P. aeruginosa
,
P. plecoglossicida
, and
P. mosselii
, respectively. Due to the inherent ability of protease, cellulase, and
HCN production by
P. plecoglossicida
and
P. mosselii
and
P. aeruginosa
, these PS
strains were suggested to be developed as biofertilizers and biocontrol agents (Jha
et al.
2009
).
The extracellular chitinase and an antifungal compound produced by
Chromobacterium
sp. strain C61 were investigated by Kim et al. (
2014
) to elucidate
their biological control activity. They observed that strain C61 had antifungal
activities under in vitro conditions and successfully controlled plant diseases in
field conditions. The bacterium possessed a locus
chi54
encoding chitinase, while
chi54
mutant did not produce chitinase. The wild-type strain showed significantly
increased production of the extracellular enzymes and expression of the
chi54
transcript, when grown in culture medium treated with chitin. Furthermore, the
in vitro assays demonstrated that purified chitinase inhibited spore germination of
multiple pathogens. However, the in planta biocontrol activity of filtrates of cul-
tures grown in the presence of chitin was lower than that of filtrates grown without
chitin indicating that correlation between chitinase and biocontrol activity was
missing. The further analysis of C61 culture filtrates revealed an antifungal cyclic
lipopeptide, chromobactomycin, whose structure contained a unique nonameric
peptide ring. The purified chromobactomycin inhibited the growth of several
phytopathogenic fungi in vitro, and plant application significantly reduced disease
severity for several pathogens. These data suggest that both the extracellular
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