Pantnagar Journal of Research

Abstract

Plants associated with endophytes are imbibed with beneficial growth promoting and biocontrol activity against phytopathogens are sustainable alternative to the synthetic fungicides. In the study, bacterial endophytes isolated from Brassica spp. were screened for antagonistic activity against Alternaria brassicicola, causing black spot disease in mustard. Bacterial isolate exhibiting 58.14 % mycelial inhibition rate was selected and identified based on 16S rRNA gene sequences as Bacillus subtilis strain and examined for further preliminary in vitro assays showing direct antagonism and inhibition of the pathogen. Microscopic studies showed irregularities in mycelium growth, aberrations in the spores’ structure and cell integrity after interacting with bacterial cells. In the buried slide experiment, the antagonistic isolate was in physical contact with the pathogen. The results showed stunted spores, uneven germination, plasmolysis of cellular components, and distorted hyphae, restricting the proliferation of the mycelial network over a 72-hour period in inoculated soil. The potential of bacterial cells as a foliar treatment to control black spot was evaluated through a detached leaf assay every 24 h for 3 days. A significant control of necrosis progression was observed in the bacterial cell inoculated leaf with respect to control. In the control, black-brown necrotic lesions encircled by a distinct yellow halo were observed after 24 hrs, and after 72 hpi, lesions of size 13 mm with extensive chlorotic regions were observed whereas in treatment, no lesions developed after 48 h and the lesion was 1.7mm after 72 hpi. The results indicate that, with optimised augmented inoculation, bacterial cells could be employed in disease management as soil and foliar treatments in further in vivo experiments.