The antagonistic ability of some strains of
Bacillus sp. was shown by the ability to control the growth of
D. bryoniae DB-01 mycelium on 1/5 PDA.
Bacillus sp. showed good inhibitory effect on hyphal growth of
D. bryoniae strain DB-01. The antifungal efficiency against
D. bryoniae strain DB-01 of tested
Bacillus strains was from 18.5 to 28.3% at 6 days after fungal inoculation. By ten days after fungal inoculation, the ability of the tested bacterial strains to inhibit the growth of
D. bryoniae hyphae was more obvious. The antagonistic performance of
Bacillus sp. S1F3, S18F11 and S20D12 reached values of more than 50%.
Bacillus sp. S20F12 was the strongest inhibition of the growth of mycelia of
D. bryoniae DB-01 with an antagonistic efficiency of 65.7% (Table 1).
Bacillus species are widely used to promote plant growth and control plant diseases (Keinath, 2016; Jangir, 2018; Ngangom
et al., 2019; Miljaković
et al., 2022). The
Bacillus genus is known for producing many endogenous biological active ingredients such as bacteriocins and lipopeptides that inhibit pathogens and prevent some harmful diseases on plants
(Pradhan et al., 2018; Rodriguez et al., 2018). Previous studies indicated that the fungal inhibition of
Bacillus species is influenced by its production of antifungal antibiotics such as bacilysisn, inturin, fengycin, bacillomycin, surfactin, ericin, mersacidin, subtilosin, subtilin and mycosublilin
(Mora et al., 2011; Rodríguez et al., 2018). Based on this mechanism, the ability of antagonistic bacteria to control fungi (or % antagonistic efficiency) is calculated based on the ability to inhibit the growth of fungal mycelium
(Le et al., 2019). When testing the antagonistic effectiveness of bacteria in
in vitro conditions, the results showed that all tested
Bacillus strains demonstrated the ability to inhibit the growth of
D. bryoniae fungal mycelium on 1/5 PDA. Recently, Ngo
et al. (2023b) also reported that
Bacillus sp. S18F11 and S20D12 had inhibitory effect on the hyphal growth of
D. bryoniae strain DB-03 on 1/5 PDA, the antagonistic performance of
Bacillus sp. S1F3, S18F11 and S20D12 reached values of more than 50% and
Bacillus sp. S20F12 had highest inhibition of the growth of mycelia of
D. bryoniae strain DB-03 with an antagonistic efficiency of 60.7%. Therefore,
Bacillus sp. S20D12 and S1F3 were high efficacy in antagonistic performance against
D. bryoniae under
in vitro.
A bacterial strain capable of limiting pathogens in
in vitro conditions is a prerequisite for limiting diseases in greenhouse conditions. However, the ability to control the development and growth of fungal mycelium under
in vitro conditions still does not have enough data to ensure the ability to limit diseases in greenhouses because it still depends on the ability to survive and produce toxic substances, antifungal agents in greenhouse conditions.The results of testing for prevention of
Bacillus sp. strains to gummy stem blight of watermelon plants inoculated with
D. bryoniae strain DB-01 under greenhouse conditions were shown in Table 2 and Table 3. Table 2 shown a significant difference in the disease incidence of the plants that were inoculated with
D. bryoniae strain DB-01 in the treatments treated with all
Bacillus sp. strains compared to the control. The plants of seeds soaked with bacterial suspension of
Bacillus strains had a lower disease incidence than that of the control. At 7 days after fungal inoculation, the plants treated with
Bacillus sp. S18F11 and S1F3 had the lowest disease incidences by 20.0 and 23.3%, respectively. The plants with low disease incidence changed at the following observation times. At 21 days after fungal inoculation, disease incidences were low in the plants treated with
Bacillus sp. S20D12 and S1F3 by 46.6 and 50.0%, respectively. Table 3 also indicated that all tested
Bacillussp. strains were significantly preventing watermelon from disease infection at 7, 14 and 21 days after fungal inoculation. The plants treated with
Bacillus sp. S20D12 and S1F3 were also low disease severity by 15.3 and 20.6%, respectively, at 21 days after fungal inoculation (Table 3).
The results also indicated that the disease incidence of plants treated with
Bacillus sp. S1F3 and S20D12 at 14 and 21 days after fungal inoculation had no change (46.6% and 50.0%) (Table 2), but the disease severity had differences after 14 days after fungal inoculation (17.3% and 12.6%) and 21 days after fungal inoculation (15.4% and 13.3%) (Table 3). This demonstrates that the plants treated with
Bacillus sp. S1F3 and S20D12 were prevented from the disease infection over time. The ability to control of the disease damage by
Bacillus sp. S20D12 and S1F3 has a slower progression but was more effective than other
Bacillus sp. strains in this study.
After 7 days of fungal inoculation, the plants only shown symptoms of gummy stem blight, which were small, brown spots on the leaves or, more seriously, large-scale leaf lesions or long-lasting cracks on the stems. Then, some plants shown more severe disease, causing the plants to wilt or part of the leaves to wither completely. However, no dead watermelon plant had been recorded yet. After 14 days of fungal inoculation, the control and
Bacillus sp. S1A1 treatment recorded a number of severely infected plants, parts gradually withered and completely withered, leading to death of plants by 13.3 and 10.0%, respectively. By 21 days after fungal inoculation, severely infected plants increased, causing plant death. Treatment with
Bacillus sp. S20D12 had no dead plants (0.0%) and with
Bacillus sp. S1F3 the plant mortality rate was only 6.6%. In the remaining treatments, the plant mortality rate ranged from 10.0 to 30.0%, while all plants in the control was dead (100%) (Table 4). The results indicated that watermelon plants were prevented from damage of gummy stem blight caused by
D. bryoniae strain BD-01 by
Bacillus sp. S20D12 and S1F13.
The results of research on the infection of
D. bryoniae strain DB - 03 was also evaluated similarly to the infection and damage of
D. bryoniae strain DB-01
(Ngo et al., 2023a). Best effectiveness in control of
D. bryoniae strain DB-03 that caused the damage to plants was
Bacillus sp. S1F3, S20D12 and S18F11
(Ngo et al., 2023b). However, the disease incidences, disease severities and plant mortality rates reached higher values compared to the treatments using
D. bryoniae DB-01 as the pathogen. This can be understood because the infection rate and pathogenic virulence of
D. bryoniae strain DB-03 were faster and stronger than strain
D. bryoniae DB-01 as previously surveyed
(Ngo et al., 2023b).
Many
Bacillus species are well known for their antagonistic activities against plant pathogens such as fungi (
Ongena and Jacques, 2008;
Raaijmakers et al., 2010; Le et al., 2019). The lipopeptide antibiotic bacillopeptin B1 produced by
Bacillus amyloliquefaciens SH-B74 could inhibit several fungal pathogens
in vitro (Ma
et al., 2014). Song
et al. (2013) also reported that lipopeptides produced by
B. amyloliquefaciens anti-CA (
Candida albicans) limit fungal growth of
C. albicans.
Bacillus amyloliquefaciens isolated from groundnut rhizosphere enhances the activities of defense enzymes through salicylic acid induced systemic resistance and several enzymes such as chitinase, peroxidase, catalase and polyphenol oxidase have strong negative correlation with disease severity index
(Rajyaguru et al., 2017). Two antagonistic bacterial strains of
Bacillus sp. S13F1 and S20D12 were originating from the stem-base of the peanut plant. At the species level, strains S1F3 and S20D12 belong to the same clade as the reference strains
B. amyloliquefaciens (Le et al., 2018). Based on the phylogenetic tree of
Bacillus strains,
Bacillus sp. S20D12 and S1F3 has a close relationship with
B. amyloliquefaciens (Le
et al., 2018), which can partly explain the similarity in the ability to control the growth of
D. bryoniae fungus in
in vitro and greenhouse conditions conducted in this study.
