M Sc

The study entitled “Endophytic bacteria for plant growth promotion and management of
web blight of cowpea” was conducted in Department of Plant Pathology, College of
Agriculture, Vellayani during 2019-2021 with the objective to evaluate endophytic bacteria
inplant growth promotion and management of web blight of cowpea. Endophytic bacteria
were isolated from healthy root, stem and leaves of fodder cowpea var. Aiswarya (22
isolates) and bush cowpea var. Bhagyalakshmi (16 isolates) from Instructional farm, COA
Vellayani and farmer’s field at Naruvamoodu respectively. The isolates were purified and
maintained for further studies. The pathogen Rhizoctonia solani causing web blight of
cowpea was isolated from infected plant samples and pathogenicity tests were carried out.
The isolates of endophytic bacteria were screened against R.solani by testing their
antagonistic properties adopting dual culture technique. The results revealed that isolate
CBRE5 (9.33 mm) showed maximum zone of inhibition against R. solani which was on par
with CBRE1 (8.83 mm) followed by CBSE5 (8.33 mm). The mycelial growth inhibition of
R. solani was recorded maximum (48.52 %) by the isolate CBRE5 followed by CBRE1
(42.22 %) which was on par with CBSE5 (41.85 %). The culture filtrate obtained from the
isolates CFLE3 and CBRE5 recorded maximum zone of inhibition against R. solani. Based
on the results of direct and indirect antagonism of endophytic bacteria, 20 isolates were
selected as promising ones for biopriming of cowpea seeds.
Surface sterilized cowpea seeds were bio-primed with selected bacterial endophytes at 108
cfu/ ml using roll towel assay. The cowpea seedlings treated with isolate CFLE3 recorded
the maximum seedling vigour index – I and II (4087.33 and 7.66 respectively) which was on
par with CBRE5 (3598.00 and 6.73 respectively) followed by CBSE5 (3452.33 and 6.70
respectively). Based on the results of roll towel assay the isolates CFLE3, CBRE5 and
CBSE5 were selected as the best three bacterial endophytes for further studies. The
promising endophytic bacterial isolates were tentatively identified as Bacillus through
morphological, cultural and biochemical characters. The identities of the species of these
isolates were further confirmed through 16S rRNA analyses as Bacillus subtilis(CFLE3), B.
amyloliquefaciens (CBRE5) and B. velezensis (CBSE5). The compatibility studiesamong the
best three bacterial endophytes following disc diffusion method and cross streak plate assay
indicated that the isolates were compatible among themselves.
In pot culture experiment, seed biopriming for 4 h along with foliar application (20 and 40
DAS) of B. velezensis CBRE5recorded minimum percent disease index (PDI) (32.33) on 14
DAI which was on par with the treatment with B. amyloliquefaciens CBSE5 (PDI- 39.33)
followed by treatment combination with B. amyloliquefaciens CBSE5 and B. velezensis
CBRE5 (PDI – 41.33). In vivo evaluation of best three endophytic bacterial isolates and
their combinations for plant growth promotion indicated that combined seed biopriming for
4 h along with foliar application of B. amyloliquefaciens CBSE5 and B. velezensis CBRE5
(20 and 40 DAS) recorded maximum values for all growth parameters viz. shoot length
(47.40 cm), root length (40.93 cm), shoot fresh weight (139.16 g), root fresh weight (49.33
g), shoot dry weight (27.83 g), root dry weight (6.33 g), pod yield (236.66 g) and number of
pods per plant (36). However, the plants treated with isolate B. amyloliquefaciens CBSE5
exhibited early flowering (33 DAS).
The best three endophytic bacterial isolates were evaluated for their plant growth promoting
traits such as production of indole acetic acid (IAA), ammonia, phosphate, siderophore and
HCN. B. amyloliquefaciens CBSE5 recorded highest IAA (3.54 μg/ml) and siderophore
(zone of colouration – 6 mm) production. Whereas, the isolate B. velezensis CBRE5 showed
highest ammonia (177.29 μmol/ml) and phosphate (zone solubilization - 2mm) production.
Thus, the present study indicated that seed biopriming for 4 h along with foliar application
(20 and 40 DAS) of B. velezensis CBRE5 was most effective treatment for the management
of web blight of cowpea whereas combined seed biopriming for 4 h along with foliar
application (20 and 40 DAS) of B. amyloliquefaciens CBSE5 and B. velezensis CBRE5 was
the best treatment in plant growth promotion in vivo which could be further validated under
field conditions for ecofriendly and sustainable safe – to – eat crop production.