Studies On Identification Of The Causal Organism Of Sesame Fusarium Wilt And Biocontrol Based On Endophytic Bactertia

Sesame is one of the most important oil crops in China. Sesame fusarium wilt occurred seriously in recent years and caused serious economic losses in sesame production. To clarify the causal organism of the disease, and to search effective control measures against the disease. Isolation and purification of the pathogen were conducted. Pathogenicity of the isolate (ZY-2) to sesame seedlings was confirmed based on Koch’s postulates. Morphological and biological characterizations of the pathogen were performed. Molecular identification of the pathogen was carried out based on the sequences of ribosomal DNA internal transcribed spacer (rDNA-ITS) and translation elongation factor la gene(tef). Biological control of sesame fusarium wilt was performed using endophytic bacterial isolates. The main results were summarized as follows:1. According to pathogen pathogenicity, morphology and sequences of rDNA-ITS and tef gene sequences, the isolate ZY-2was identified as a member of Fusarium oxysporum. The temperatures suitable for growth of the pathogen were22-34℃with28℃as the optimum. The pathogen grew well at a pH range of2.5-9.5with6.5-7.5as the optimum. Sucrose, glucose, sodium nitrate and ammonium chloride were most suitable for the growth of the pathogen. The pathogen could not sporulate on the medium containing glucose and L-proline as solo carbon and nitrogen sources, respectively. The pathogen could produce pectinase and protease, but could not produce lipase, amylase and cellulase.2. A total of166endophytic bacterial isolates were isolated from healthy sesame plants, and64of them had inhibitory activities against F. oxysporum, contributing to38.55%of the isolates obtained. The isolates B5-47, B4-5, C5-35and A4-2showed stronger inhibition effects on the growth of the pathogen. Based on in vitro and pot growth promoting tests on sesame seedlings,3endophytic bacterial isolates (B5-47, A4-2and A3-28) were screened out as biocontrol agents against F. oxysporum. According to the morphological characteristics, physiological and biochemical tests and16S rDNA sequence analysis, the isolates B5-47, A4-2and A3-28were identified as Bacillus subtilis. The optimum pH for the growth of isolates A3-28, isolates A4-2and isolates B5-47was at pH7,8and8, respectively. The optimum temperatures for the growth of isolates A3-28, A4-2and B5-47were30℃,35℃and30℃, respectively. These isolates could not use fructose, xylitol and mannitol as carbon source for their growth. The isolate A3-28could use all of the8nitrogen sources tested for its growth. The isolates A4-2and B5-47could not utilize glycine and histidine for their growth, respectively.3.-The efficacies of the endophytic bacterial isolates A3-28, A4-2and B5-47against sesame fusarium wilt were50.12%,46.29%and42.74%, respectively.