STUDIES ON ETIOLOGY AND MANAGEMENT OF BACTERIAL SOFT ROT OF CARROT
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Date
2017-08-16
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK, BENGALURU
Abstract
Bacterial soft rot is one of the major constraint in the production of carrot. The
present study describes the first report of a new pathogen on carrot causing bacterial soft
rot. Ten isolates were collected from Kolar, Chikkaballapura and Bengaluru rural districts
and pathogenicity was proved on carrot. All the ten isolates were able to infect fruits of
potato, tomato, chili and bell pepper in laboratory condition. In glass house condition the
ten isolates caused seedling symptom on cucumber, eggplant and radish indicating wide
host range of bacteria. The ten isolates were identified as Klebsiella variicola by 16S
rRNA sequencing. This is the first new report of bacterial soft rot carrot caused by K.
variicola. Bacillus velezensis strains A6 and P42 the novel biocontrol agent showed
maximum inhibition against KV2 (24.44 %) and KV1 (26.94 %) respectively. The strains
A6 and P42 were highly effective and reduced the infection of soft rot disease in both
glass house (80.00 & 77.77 % respectively) and in field condition (4.33 & 4.85 % disease
incidence respectively). The two strains possessed antimicrobial genes like Fengycin
(269bp), Bacillomycin (370 bp), Iturin (423 bp), Surfactin (201 bp), Bacilysin (498 bp)
and subtilin (375 bp). The whole genome sequencing of A6 strain revealed the genome
size of 4.23 Mb and 4303 protein-coding genes were predicted. The metabolite extracts
of A6 and P42 showed maximum inhibition against KV8 (18.61 %) and KV8 (17.50 %)
respectively. The GCMS analysis of culture filtrate revealed ten bioactive compounds
from A6 and six from P42 after derivatization of the culture filtrate, whole nonderivatization
culture filtrate of A6 and P42 identified nine and twelve bioactive
compounds.
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