MSc

The biocontrol agents play an important role in the plant disease
management and growth promotion. They are eco-friendly and low cost
agricultural inputs. One of the major constraints in the use of biocontrol agents, is
the survivability of inoculated cultures till the end of the crop period. So, there is a
need to enhance the survivability of the biocontrol agents for the management of
soil borne pathogens and growth promotion. Trichoderma and Bacillus sp. are two
well-known biocontrol agents for plant disease management and growth
promotion. Cowpea is one of the most popular, protein rich legume crop of Kerala.
One of the major constraints in the cowpea production is the diseases like collar-
rot (Rhizoctonia solani) and root rot (Pythium aphanidermatum) which have
become a serious threat. Since, no studies have been conducted in Kerala on the
biofilm based inoculants, an attempt was made to increase the survivability of
Trichoderma and Bacillus through biofilm based inoculants for the management of
two major soil borne diseases and growth promotion in cowpea.
Rhizosphere soil samples were collected from ten different cowpea growing
areas of Thrissur district. The maximum population of Trichoderma sp. (4.8 × 103
cfu g-1) and Bacillus sp. (4.48 × 105 cfu g-1) were recorded in Chellakara and Mala,
respectively.
A total of nine Trichoderma sp. and five Bacillus sp. were obtained. They
were screened for plant growth promoting and antagonistic activities. Among
Trichoderma sp., maximum IAA production (24.03 μg ml-1) was recorded by TCK-
2 (Chalakudy) followed by TML (Mala) (14.77 μg ml-1). TML (Mala) isolate was
the most efficient P solubilizer (147.2 μg/ml). Among Bacillus sp., maximum IAA
production (6.20 μg ml-1) and maximum P solubilization (151.3 μg ml-1) were
recorded by BCH (Chellakara) isolate.
Among Trichoderma sp., TCH-1 (Chellakara) and TMT (Mttathur) were
positive for HCN production and TCH-1, TMT, TMS, TPZ and TCK-1 were
positive for ammonia production. Among Bacillus sp., BCH (Chellakara) and BMT
(Mattathur) were positive for HCN production and all five isolates (BCH, BML,
BMS, BPN and BMT) were positive for ammonia production.
Both Trichoderma sp. and Bacillus sp. were screened in vitro for their
antagonistic activity against Rhizoctonia solani and Pythium aphanidermatum.
Among Trichoderma sp., TCH-1 (Chellakara) isolate recorded maximum
inhibition (51.1%) against Rhizoctonia solani and Pythium aphanidermatum
(57.7%).
Bacillus sp. isolates were screened for biofilm production and highest
biofilm production was recorded by BCH (Chellakara) (0.060) followed by BPN
(Pazhayanur) (0.058) isolates.
Based on the PGPR traits, per cent inhibition and biofilm production under
in vitro, three most promising Trichoderma sp. (TCH, TMT, TPZ) and Bacillus sp.
(BCH, BPN, BML) were subjected for mutual compatibility studies. All the
selected Trichoderma sp. and Bacillus sp. were mutually compatible with each
other.
The isolates of TCH (Chellakara) + BCH (Chellakara), TPZ (Pazhayanur)
+ BPN (Pazhayanur) and TMT (Mattathur) + BML (Mala) were selected for the
biofilm based inoculant production. Among the different carrier materials for
biofilm based inoculant production talc powder was the most promising carrier
material due to highest population of isolates at 90 DAI.
Biofilm based inoculants were evaluated under pot culture for the
management of collar rot (Rhizoctonia solani) and root rot (Pythium
aphanidermatum) in cowpea under two separate experiments. Based on the
biometric parameters, collar rot and root rot disease management and yield
parameters, biofilm based formulation of TCH (Chellakara)+BCH (Chellakara)
(T2) was the most promising treatment for the management of collar rot disease and
growth promotion in cowpea, which was on par with the PGPR Mix- II (T9).
Population of inoculated Trichoderma sp., Bacillus sp. and Rhizobium sp.
indicated declining trend till the final harvest of the crop. The population decreased
from 108 cfu ml-1 to 104 cfu ml-1. However, biofilm based inoculant showed highest
population of Trichoderma sp. and Bacillus sp. at the time of harvest.
The three best promising Bacillus sp. isolates were identified through 16S
rRNA sequencing and identified BCH isolate as Bacillus subtilis, BPN as Bacillus
velezensis and BML as Bacillus megaterium.