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[Display omitted] • Bacillus amyloliquefaciens HSSN09 with antagonistic effect on FON was isolated. • B. amyloliquefaciens HSSN09 could effectively control watermelon Fusarium wilt and promote the growth of watermelon seedlings. • Tacrolimus has a very obvious antifungal effect and can be used to control watermelon Fusarium wilt. • Tacrolimus was also able to stimulate the growth of watermelon seedlings. • Tacrolimus or its analogs may play a role as a pleiotropic factor in B. amyloliquefaciens HSSN09 biological control. Watermelon Fusarium wilt caused by Fusarium oxysporum f. sp. niveum (FON) is one of the most devastating diseases in watermelon production. Biological control approaches are efficient and environmentally-friendly, thus have aroused broad interest. However, only a few biocontrol factors/molecules have been characterized due to varied genomes and diversified secreted secondary metabolites of biocontrol microorganisms. We report the screen and identification of a Bacillus amyloliquefaciens strain HSSN09 with high antagonism to FON and watermelon growth promotion capacity. B. amyloliquefaciens HSSN09 and its secondary metabolites showed inhibition on FON mycelial growth, spore formation and spore germination. Metabolomes of the highly antagonistic strain B. amyloliquefaciens HSSN09, medium antagonistic strain B. amyloliquefaciens FGW53, weakly antagonistic strain B. subtilis JC03 and non-antagonistic strain B. cereus FGW109 were compared with LC-MS/MS. By antagonistic assay, tacrolimus was screened out among the 531 molecules that appeared in the sequencing results of HSSN09 metabolome but not in that of the non-antagonistic strain without significant inhibition on the growth of FON. Among the four tested Bacillus strains, tacrolimus analogue was only observed in the supernatant of HSSN09 by HPLC and MALDI-TOF-MS. We further confirmed the ability of tacrolimus to suppress FON and promote watermelon seedling growth. [ABSTRACT FROM AUTHOR]

Plant gray mold disease caused by necrotrophic pathogen Botrytis cinerea , has been a serious threat to many important crops. It is urgent and necessary to seek an effective and environmentally friendly control strategy to control grey mold disease during the crop production. Moreover, it is also urgently needed to clear understand how the strategy works. To screening an efficient biocontrol agent in control of gray mold disease caused by B. cinerea , one hundred strains, which have the potential in controlling plant diseases, were selected from our laboratory’s strain library, and employed to our research. The results in the study indicated that Bacillus velezensis could act as a potential and efficient biocontrol agent (BCA), and two B. velezensis strains 5YN8 and DSN012 were screened out with high antagonistic and hydrolase activity, which could significantly control pepper gray mold disease and promote the pepper growth. Further deeply study on biocontrol mechanism indicated that B. velezensis could suppress the growth and spore formation of B. cinerea by secreting some secondary metabolites or releasing numbers of volatile organic compounds (VOCs). In the other hand, we also found that B. velezensis could trigger plant basal immunity. The BCA could increase the expression of SA signal markers and plant defense related genes. It was able to induce hydrogen peroxide accumulation and plant related enzyme activities in leaves of pepper as well. This study provides another high-efficiency, and potential strategies for the biological control of gray mold disease. It is the first report of B. velezensis strain which can control gray mold disease, In addition, it is also the first to comprehensively illustrate how the strains can efficiently protect pepper from B. cinerea attacking. [ABSTRACT FROM AUTHOR]

Abstract: Biocontrol efficiency of various Bacillus preparations (BB11 and FH17 strains, and a mixture of both strains (BF) at a 1:1 ratio by concentration) and different application methods against Phytophthora blight of bell pepper were studied. The application methods included (A) mixing (mixing BF with rapeseed residue and then immediately applying in the field), (B) composting (mixing BF with rapeseed residue and made compost before application), (C) spraying (spraying diluted BF into field or rhizosphere of plants), and (D) watering (watering diluted BF into field or rhizosphere of plants). In greenhouse experiments, the addition of BF increased biocontrol efficiency (60.3%), and yield increase (200%) was better than with BB11 (55.8 and 80.6%, respectively) or FH17 (37.1 and 50.0%, respectively). In field trials at Huai’an in 2001, the best dosages of BF mixture (1010 cfu/ml) with the four above-mentioned application methods were 15, 7.5, 15, and 22.5L/ha, respectively. When preparations were applied at the best dosage in the same field, the BF mixture provided superior biocontrol efficiency and greater yield increase with treatment B than those with treatment A or C. Combining the field trial results from 2002 to 2003 at Huai’an and Wu’han, the total average control efficiencies and yield increases for treatments A, B, and C reached 81.0, 88.0, and 79.1% and 33.1, 44.3, and 29.1%, respectively, with their best dosages. However, method B, composting, provided better disease control and greater yield increases than all other methods, and did so at a lower application rate. [Copyright &y& Elsevier]