Suppressive effects of Bacillus spp. on mycelia, apothecia and sclerotia formation of Sclerotinia sclerotiorum and potential as biological control of white mold on mustard

Biological control, especially with Bacillus-based biocontrol agents, offers an attractive alternative to synthetic pesticides for sustainable management of white mold disease caused by Sclerotinia sclerotiorum. In this study, eight effective Bacillus isolates were isolated from rhizospheric soil samples as potential bacterial biocontrol agents. Cultural, biochemical, and molecular analyses of 16S rDNA and gyrase subunit A (gyrA) confirmed that all isolates were identified as Bacillus amyloliquefaciens subsp. plantarum. The production of hydrolytic enzymes and the plant growth-promotional attributes of these isolates confirmed their multifaceted potential. Molecular analysis of the eight biosynthetic genes, which are related to antibiotic properties of bacilli, revealed that all of the isolates possess five genes: bacA for bacilysin, dfnM for difficidin, fenA for fengycin, ituA for iturin, and sfp for surfactin. The Bacillus isolates inhibited mycelial growth and suppressed formation of sclerotia during an in vitro test against S. sclerotiorum. Deformities and cell-wall lysis of mycelia, abnormalities of apothecia, and germination failure of ascospores through interaction with the Bacillus isolates were observed with light and scanning electron microscopes, suggesting that they have high antagonistic effects against S. sclerotiorum. Seed bacterization with the Bacillus isolates protected mustard seedlings in vitro up to 98 % against S. sclerotiorum. In a pot experiment, damages of mustard plants against the pathogen decreased up to 90 % after foliar spray of the Bacillus isolates. In addition, the isolates increased seed germination and accelerated seedling vigor of mustard, suggesting that they have plant growth-promoting functions.