| Passion fruit(Passiflora edulis)is a plant in the family Passifloraceae,which has a large planting area in Yunnan,Guangxi,Guangdong,Fujian,Taiwan and other provinces of China.Passiflora edulis possesses superior economic benefit because of its excellent edible value.In addition,it also owns medicinal value and processing potential of by-products,which endows it with favourable industrial development prospect.Passiflora edulis often faces the threat of many diseases during its growth,including viral diseases,bacterial diseases and fungal diseases.Among fungal diseases,basal stem rot is one of the most common diseases,and the pathogen is Fusarium solani.For fungal diseases,chemical control is still the most common control measure at present,and biological control has achieved certain development in recent years due to advantages such as a reduced burden on the environment.In order to broaden biocontrol pathway for controlling basal stem rot in Passiflora edulis,this study screened microorganisms from the soil and fallen leaves on the ground,and isolated a bacterial strain that demonstrated a growth inhibitory effect on F.solani.Based on morphological,physiological and biochemical characteristics and phylogenetic analysis of 16 S r DNA,gry A,gry B,and rpo B genes,the bacterial strain was identified as Bacillus velezensis.The fermentation conditions of this strain were preliminarily explored.It was found that temperature was the main factor affecting its growth and antifungal activity of its fermentation broth.The established fermentation conditions were culture at 39 °C and an initial p H 7.0 with shaking at 180 revolutions/minute for 12 hours.From the fermentation broth,a type of antifungal peptides(named BVAP)was purified by employing anion exchange chromatography on Q-Sepharose and Mono Q,followed by gel filtration chromatography on Superdex 75.BVAP exhibited a molecular weight of circa 1.5 k Da as judged by polyacrylamide gel electrophoresis(tricine-SDS-PAEG)and mass spectrometry(MALDI-TOF MS),and it was preliminarily analyzed as belonging to fengycin family.BVAP could not inhibit the spore germination of F.solani in vitro,but it caused aberrant spore germination,and its half-effective concentration was 11.63 μg/m L.In addition,BVAP inhibited mycelial growth in F.solani with a half-inhibitory concentration of 5.58 μg/m L,which was significantly better than those of the chemical fungicides thiram(41.24 μg/m L)and hymexazol(343.31 μg/m L).The antifungal activity of BVAP displayed remarkable thermal stability and acid stability: its activity remained stable after heating at 50-100 °C or incubation with solutions of p H 1-3.However,its activity did not show pronounced stability in the presence of alkali since there was a complete loss of activity after exposure to a solution of p H 13.Preliminary studies on the action mode of BVAP were performed.The results revealed that BVAP brought about swelling at the tips of F.solani hyphae and made the hyphae prone to rupture.In addition,BVAP increased the permeability of mycelial membrane,resulting in abnormal accumulation of nucleic acids and chitin at the sites of swelling in the mycelium.The above research findings disclosed that the antifungal peptides produced by B.velezensis exhibited a superior biocontrol potential toward the important pathogenic fungus F.solani,and it is expected to provide more references as a basis for exploiting B.velezensis or its antifungal peptides for the prevention and control of plant fungal diseases. |
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