7.7 Bacterial Endophytes as Biocontrol Agents for Wilt
Endophytic bacteria isolated from live oak stem showed in vitro antagonism against
Colletotrichum fagacearumcausing Oak wilt (Brooks et al. 1994 ). The endophytic
bacteriumBurkholteria cepacia, isolated fromAsparagusexhibited antagonistic
activity against banana wilt (Pan et al. 1997 ). Tomato seedlings treated with
endophyticP.fluorescensas seedling dip increased resistance to wilt disease
(M’Piga et al. 1997 ). Endophytic bacteria isolated from potato tubers showed better
antagonistic activity againstF. avenaciarum, F. sambucinumandF. oxysporum
causing wilt of many tuber and commercial crops (Sturz et al. 1999 ).
Endophytic bacteria isolated from mustard and tomato plants, completely
inhibited the mycelail growth ofV. dahliaeandF. oxysporumf.sp.lycopersici
in vitro and in vivo, it reduces the disease incidence and also increases the plant
growth parameters (more than 75% and increased the plant height and shoot dry
weight) (Nejed and Johnson 2000 ). EndophyticPseudomonassp. (PDBCEN 8)
exhibited maximum mycelia growth inhibition ofFusarium udumon PDA. They
also recorded that endophyticPseudomonassp. (PDBCEN 7) exhibited maximum
inhibition ofR. solanion PDA. The same trend was followed in the endophytic
Pseudomonassp. (PDBCEN 3) against tomatoFusariumwilt (Rangeshwaran et al.
2002 ). Bhowmik et al. ( 2002 ) isolated endophytic bacteria from root and stem
region of cotton seedlings and tested for its antagonistic activity against two fungal
and one bacterial disease in cotton. Among these,five pseudomonads were highly
antagonistic toR. solani, S. rolfsiiandX. axonopodispv.malvacearum(O’Sullivan
and O’Gara 1992 ). Nagarajkumar et al. ( 2004 ) also reported that the production of
siderophores, secondary metabolites and cell wall degrading enzymes by
Pseudomonasstrains may be responsible for the effective control of plant pathogens
includingF. oxysporumandR. solani. Ziedan ( 2006 ) revealed that peanut seeds
were soaked with endophytic bacterial suspensions before sowing reduced the
infection byAspergillus nigerandF. oxysporumcolonization over peanut seed at
30 days after harvesting.
The PGPR strains of Pf1 and TRC 54 were effective in reducing the mycelial
growth ofF. oxysporumf.sp.cubensein vitro. The mycelia growth inhibition might
be due to the production of enzymes and antibiotics by PGPR strains (Akila et al.
2011 ). Nandhini et al. ( 2012 ) who reported that entophytic bacteria were isolated
from root, stem, leaves and fruits and tested for its antagonistic activity against
Fusariumwilt disease in tomato. All the isolates belonging to four bacterial genera
viz.,Bacillus, Pseudomonas, KlebsiellaandCitrobacter. The results revealed that
only 50% of the isolates exhibited strong antagonistic activity against tomato wilt
pathogen. Sundaramoorthy et al. ( 2012 ) who reported that the consortium of rhi-
zospheric and phyllospheric bacterial strains (P.fluorescens(Pf1) andB. subtilis
(EPCO16 and EPC5) strains) reducedFusariumwilt incidence in chilli by 17–30%
compared to control plants.
7 Role of Bacterial Endophytes in Plant Disease Control 143