MSc

The study named “Plant growth promotion and foot rot disease management
in black pepper by Bacillus spp.” was conducted in Department of Agricultural
Microbiology, College of Agriculture, Vellayani and Coconut Research Station,
Balaramapuram, during the academic year 2019-2022. The objective of the study
was to assess the effects of endospore-forming Bacillus spp. on growth and foot rot
disease suppression in black pepper in the nursery.
Experiments comprised both in vitro and in vivo studies. In in vitro
interaction, dual culture plate assay was done to assess the antagonistic effect of
bacterial isolates against P. capsici.
All the three bioagents used were proven to be antagonistic to P. capsici. B.
pumilus VLY17 showed the maximum zone of inhibition whereas B.
amyloliquefaciens VLY27 showed the least zone of inhibition. No inhibition on
mycelial growth of P. capsici was observed on treatment with culture filtrate in agar
well diffusion assay.
In detached leaf assay screening, significant difference was observed in
lesion size developed on leaves treated with bacterial suspension compared to that
on control leaves treated with sterile water. On 2DAI, leaves dipped in B. pumilus
VLY17 showed the least lesion size whereas on 3 DAI, leaves applied with
consortium of the bacterial isolates showed the least lesion size.
Bio agents were characterized to check the production of plant growth
promoting and disease suppressing metabolites. All the three isolates showed
significant amount of IAA production. B. velezensis PCSE10 produced higher IAA
(15.10 ppm) when estimated without adding tryptophan whereas B.
amyloliquefaciens VLY27 produced maximum IAA (23.34 ppm) when medium
was supplemented with L-Tryptophan. None of the strains could produce HCN
under in vitro conditions. B. amyloliquefaciens VLY27 and B. velezensis PCSE10
used produced Ammonia. None of the bacterial isolates used showed siderophore
production and phosphate solubilization.
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Bacterization with B. pumilus VLY17 showed the maximum establishment
of cuttings, maximum number of leaves per plant, maximum shoot length and
longest root length, maximum root volume and maximum fresh weight and dry
weight of newly emerged shoot and leaves as well as roots throughout the
experimental duration. Even though fresh weight of roots increased on
bacterization, no significant difference was observed in statistical analysis
compared to control. Plants treated with B. amyloliquefaciens VLY27 showed the
maximum number of roots per plant.
Suppression of Phytophthora foliar infection on bacterization was
evaluated in the nursery. On analysis significant difference was observed in lesion
size on treatment with bacterial suspension compared to pathogen inoculated
control. The least lesion size was observed on treatment with B. pumilus VLY17.
The treatments also showed significant effect on disease index.
Abundance of root colonization by endospore forming bacterial isolates was
checked to ascertain if the plant growth promotion as well as the disease
suppression was brought about by the endospore-forming bacterial isolates.
Colonization of endospore formers was found to be maximum on roots of plants
treated with consortium of bacterial isolates.
From the present study, it is concluded that endospore-forming bacteria used
in the study have plant growth promotional activities and biocontrol potential
against the pathogen P. capsici, which causes foot rot in black pepper.