TITLE:
Testing of Bacterial Endophytes from Non-Host Sources as Potential Antagonistic Agents against Tomato Wilt Pathogen Ralstonia solanacearum
AUTHORS:
Pious Thomas, Reshmi Upreti
KEYWORDS:
Bacterial Wilt, Biocontrol, Endophytic Bacteria, Growth Promotion, Solanum lycopersicum
JOURNAL NAME:
Advances in Microbiology,
Vol.4 No.10,
August
27,
2014
ABSTRACT:
The study was taken up with the
objective of testing whether the endophytic organisms isolated from crops that
are normally non-hosts to the bacterial wilt pathogen Ralstonia solanacearum possessed pathogen-antagonistic activity and
to evaluate the selected isolates for the alleviation of wilt disease in the
target tomato crop through horizontal movement of promising organisms. Sixteen
endophytic bacteria (EB) isolated from the micropropagated cultures of grape,
watermelon and papaya were tested for potential antagonistic effects against R. solanacearum tomato isolate “NH-01”
through agar-well diffusion assay. Enterobacter
cloacae from papaya (EB-11) displayed the maximum antagonistic effect
followed by Bacillus subtilis (EB-06)
and B. flexus (EB-07) from watermelon
and B. pumilus (EB-02) from grape.
Testing the above organisms for crop protection through seed fortification of
susceptible tomato cv. Arka Vikas at sowing in R. solanacearum inoculated (Ral+) organic cocopeat showed EB-02 and EB-11
promising (33% and 32% survival, respectively, four weeks after sowing against
15% in Ral+ control). A second trial
showed 37%, 28%, 21% and 55% seedling survival 6 weeks after sowing for EB-02,
EB-06, EB-07 and EB-11 respectively, compared to 2.5% in non-treated control.
Assessing the four endophytes for crop protection in Ral+ sick-soil through seedling fortification at transplanting
indicated less disease incidence in treated sets (40%, 40%, 20% and 20%
survival, respectively, six weeks after transplanting) over non-fortified
control (5%). Endophytic fortification of seedlings through hypocotyl
inoculation showed some systemic resistance induction upon seedling
transplanting to sick soil but not with petiole fortification. Seedling growth
was enhanced by the isolates EB-06 and EB-07. The study thus identifies four
endophytic organisms from crops unrelated to tomato possessing potential
antagonistic activity against the wilt pathogen and prospects for exploitation
as biocontrol agents coupled with seedling growth promotion effects.