Preliminary Study On Biocontrol Mechanisms Of Streptomyces Spectabilis FY-1 Against Gaeumannomyces Tritici

Take-all is one of the destructive root diseases on wheat.At present,fungicide is major method for control of this disease.However,the widespread use of fungicides will not only cause resistance of pathogenic fungi,but also bring fungicide residues.In recent years,biocontrol has become a green and environment-friendly method to partial replace fungicide.In this study,the antifungal bacteria were isolated from the rhizosphere soil against Gaeumannomyces tritici(Ggt),and its taxonomic status,fermentation conditions,antifungal substance properties and growth promoting effect were studied.The main findings are as follows:The antagonistic bacteria FY-1 was isolated from the rhizosphere soil of diseased wheat in the major wheat-producing area(Suzhou,Anhui).It has obvious inhibition effect on Ggt.According to colony morphology,physiological,biochemical characteristics and molecular identification,FY-1 was identified as Streptomyces spectabilis.The Streptomyces FY-1 inhibition rate of the Ggt was 60.26%.The best antifungal effect of FY-1 is against Bipolaris maydis,with inhibition rate at 60.83%.The inhibition rate against different pathogenic fungi such as Colletotrichum gloeosporioides and Fusarium oxysporum is above 50%.It showed that FY-1 had broad spectrum antifungal activity.Streptomyces FY-1 induce the mycelium of Ggt enlarged,distortion and abnormal tips of hyphae.The inhibition rate of FY-1 spore suspension is 52.12%,and that of sterile fermentation broth is 59.13%,and the antifungal substance is non-volatile.In the environment of strong acid and alkali,the antifungal effect of sterile fermentation broth is significantly reduced.The inhibition rate of the sterile fermentation broth in water bath with temperature over 40℃ decreased obviously,and the antifungal rate at 80℃ decreased to 10%.Antifungal substance of Streptomyces FY-1 is not sensitive to protease K,but sensitive to chloroform.It is preliminarily presumed that the antifungal substance is a small molecule compound,and there are no ester bonds and peptide bonds adjacent to the C-terminal of aliphatic amino acids and aromatic amino acids in the compound.Ethyl acetate was used to extract the sterile fermentation broth of Streptomyces FY-1.The results showed that the antifungal substance of FY-1 was polar substance and dissolved in water.The inhibition rate of the water crude extract against the Ggt reaches 100%.Organic phase has no antifungal effect.The crude extract has stable antifungal activity in acid-base and high-temperature environments.The optimal fermentation conditions for Streptomyces FY-1 was determined.The best nutrition is in 40 m L/250 m L PDB with p H=7,and incubated at 30℃ for 5 d.Pot experiments show that Streptomyces FY-1 has a certain germination promoting effect on wheat seeds.The germination rate of wheat seeds is increased by 5% after being treated with FY-1 fermentation broth.The plant height of wheat increased by FY-1 fermentation broth at 3.5 cm compared with the control group.In summary,S.spectabilis FY-1 can be used as a biocontrol strain to prevent and control take-all of wheat,and its antifungal substances have good inhibitory effect on Ggt.