Agriculture Reference
In-Depth Information
2.3.6 Production of Lytic Enzymes
In high input modem agricultural practices, pesticides are frequently and inappro-
priately used to protect crop plants from damage by insects, disease and so on which
today still destroy almost 33 % of all food crops. The use of pesticides in this
respect is considered effective if they provide the desired biological results and are
inexpensive. However, the indiscriminate use of pesticides has resulted in the
adverse impact on soil fertility, human health and the environment. Therefore,
one of the safest strategies involving microorganisms for controlling/managing
plant pests often called as “biocontrol” holds great promise as an alternative to
the use of synthetic agrichemicals. Biological control agents are generally consi-
dered more environmentally sound than the pesticides and other antimicrobial
treatments. In this context, the antagonistic potential of microbes in particular has
formed the base for effective applications of such organisms as an alternative to the
chemical control measures against a range of fungal and bacterial plant pathogens.
And hence, a variety of microbial compounds have been identified/extracted that
have been found to inhibit/suppress the phytopathogenic growth leading thereby to
the reduction in damage to plants (Helbig
2001
; Yang et al.
2005
; Raza et al.
2008
).
These microbially synthesized compounds include defence enzymes, such as
chitinase,
β
-1,3-glucanase, peroxidase, protease
and lipase
(Bashan and
de-Bashan
2005
; Karthikeyan et al.
2006
). Chitinase and
-1,3-glucanase degrade
the fungal cell wall and cause lysis of fungal cell. Furthermore, chitin and glucan
oligomers released during degradation of the fungal cell wall by the action of lytic
enzymes act as elicitors that elicit various defence mechanisms in plants. Such
enzymes produced by
Pseudomonas stutzeri
have demonstrated the lysis of the
pathogen
Fusarium
sp. (Bashan and de-Bashan
2005
). Peroxidase (PO) represents
another component of an early response in plants to pathogen attack and plays a key
role in the biosynthesis of lignin which limits the extent of pathogen spread (Bruce
and West
1989
). In bean, rhizosphere colonized by various bacteria induced PO
activity (Zdor and Anderson
1992
). In a study, a rapid increase in PO activity was
recorded in coconut (
Cocos nucifera
L.) treated with a mixture of
P. fluorescens
,
T. viride
and chitin which contributed to induced resistance against invasion by
Ganoderma lucidum
, the causal agent of
Ganoderma
disease (Karthikeyan
et al.
2006
). These findings suggest that PGPR possessing the ability to synthesize
hydrolytic enzymes can effectively be utilized for managing the plant diseases and
can help to reduce the pesticide usage.
β
2.4 Conclusion
In intensive agricultural practices, P is supplied to plants through synthetic phos-
phatic fertilizers, which indeed is expensive and environment disruptive. Appli-
cation of phosphate-solubilizing microorganisms as an alternative to chemically
