Abstract
Sclerotinia sclerotiorum, as a newly emerged phytopathogen, was found to cause
white mold disease of many plants including different fields and horticultural
crops in recent years in Bangladesh. Biological control of white mold disease as
eco-friendly approaches for sustainable management of the fungus is important.
In this study, characterization of S. sclerotiorum and its biological control as
ecofriendly approach with Bacillus spp. were studied. For characterization of S.
sclerotiorum, a total of 36 fungal isolates were collected from infected plant parts of
different hosts and their morpho-physiological characteristics were studied.
Molecular detection up to species level was confirmed through internal
transcribed spacer (ITS) sequencing. On the other hand, 15 effective Bacillus strains
were selected from total of 150 bacterial isolates collected from rhizospheric soil
samples and dead sclerotia of the fungus. Potential Bacillus strains were screened
primarily by dual culture technique. Then they were characterized through
different biochemical, and molecular analyses of 16S rDNA, gyrA and biosynthetic
genes. The production of hydrolytic enzymes and plant growth-promotional
attributes were studied. Antagonistic effect of Bacillus SsBB-1 isolate against the
fungus was also studied by light and electron microscope. In vitro disease
suppression, plant assay and plant growth promotion assay were conducted with
the effective Bacillus isolate. Morpho-physiological and molecular characterization
proved that all the fungal isolates were of S. sclerotiorum. Among the 15 potential
Bacillus isolates, the most effective SsBB-1 isolate was confirmed as Bacillus
amyloliquefaciens subsp. plantarum with different biochemical, and molecular
analyses of 16S rDNA and gyrA gene. The production of hydrolytic enzymes and
the plant growth-promotional attributes of the strain were confirmed in vitro
assay. Molecular analyses of the eight biosynthetic genes revealed that the isolate
SsBB-1 possess five genes: bacA for bacilysin, dfnM for difficidin, fenA for fengycin,
ituA for iturin, and sfp for surfactin. The Bacillus SsBB-1 inhibited the growth and
development of S. sclerotiorum in vitro test. Morphological deformities, blackening
and pore formation on mycelia, abnormal apothecia and germination failure of
ascospores were found with light and scanning electron microscope during
antagonism study. Bacillus SsBB-1 protected mustard seedling up to 96.33% in
vitro. In a pot experiment, infection of mustard plants with the fungus decreased
more than 89.06% after foliar spray of Bacillus SsBB-1. The Bacillus SsBB-1 helped
to increase seed germination and accelerated the plant growth-promoting abilities
of the mustard plants.