Identification Of The Pathogen Causing Fruit Rot Disease Of Mulberry And Screening Of Biocontrol Bacteria

Mulberry is easily infected by pathogens during ripening,and sclerote disease was the most common disease on mulberry,In addition,there is also the occurrence of mulberry fruit rot,which has a negative impact on the development of mulberry industry in China.During the mulberry disease survey in May 2017,we found that mulberry fruit rot appeared in mulberry garden of yangling agricultural comprehensive experiment and demonstration station in shaanxi province,and the infected mulberry fruits showed white,or yellow and wilted.In this study,the pathogen of mulberry fruit rot was isolated and identified.The pathogenicity of the pathogen was detected according to Koch's rule,and the biological characteristics of pathogen were studied.Subsequently,the biocontrol bacillus with strong inhibition effect on pathogen was screened out in order to lay a theoretical foundation for exploring the causes and laws of mulberry fruit rot,and to provide scientific basis and new methods for the control of mulberry fruit rot.The main contents and results of this research are as follows:1?In order to indentify the causes of mulberry fruit rot disease,fungal strain was isolated from rotted mulberry fruit by conventional tissue separation.The colony was round and produced whitish aerial mycelium with purple pigments on the PDA medium.According to microscopic observation,its macroconidia was less in number with 2 to 5 septa,spindle or sickle in shape,slightly curved with sharp ends,whose size was(15.4–40.7)?m×(1.4–3.1)?m.In contrast,its microconidia was more in number with 0 to 1 septa,one tapered end and the other obtuse end,whose size was(3.3–9.5)?m×(2.0–3.8)?m.Based on observation on colony morphology and conidium morphology,it was preliminarily identified as Fusarium proliferatum.According to sequencing results after PCR amplification by universal primers of EF-1? and r DNA ITS,the pathogen causing mulberry rot disease was confirmed to be F.proliferatum.2?The pathogenicity of the strain was detected by mycelial agar discs inoculation,and it was found that F.proliferatum has a strong infectivity to mulberry leaves and fruits.The results of inoculation of living leaves in laboratory showed that black or yellow spots and a little white mildew appeared on the edges of the leaves.Progressively,these spots have deepened in color and expanded from the edge to the middle.Moreover,the white mold layer increased.Eventually the area of the spots expanded to 40%-70%,some of the infected leaves became rotten and fell off the plants 10 days after inoculation.The results of inoculation of mulberry fruits in the field showed that mulberry disease incidence in the treatment group was 100%.The whole or part of mulberry area changed from red to white,and the surrounding uninoculated mulberry was also infected.After 7 days,the white mulberry affected by the disease became yellow and the stalks also turned wilt.Ten days later,the leaves around the infected mulberry fruits also appeared yellow and withered.The same fungus was re-isolated from the artificially inoculated fruits and confirmed by morphological and molecular assays as described above,fulfilling Koch's postulates.Thus,the result showed the F.proliferatum strain was the causal agent of the fruit rot on mulberry.3?The results of biological characteristics studies showed that the optimum temperature for tis growth of F.proliferatum Z4 was 28 ?,and the optimum p H for tis growth was 7.Among different carbon sources,maltose was the best and sucrose was the worst.Among the different nitrogen sources,potassium nitrate was the most suitable one,but the utilization effect of ammonium nitrate and beef paste was the worst.4?The F.proliferatum Z4 isolated from mulberry fruit rot and the Ciboria shiraiana purchased in laboratory were used as indicator strains.Four biocontrol strains with strong inhibition on the two pathogens were screened out from the fruits of mulberry fruit rot by plate confrontation culture.The results showed that the bacteriostatic rate of the four biocontrol strains against the strain Z4 was 47.78%-56.65%,and the bacteriostatic rate of the four biocontrol strains against the C.shiraiana was 84.02%-90.10%.Through morphological and molecular biological identification,the four biocontrol strains were identified as Bacillus.