[Isolation and ARDRA analysis of cucumber entophytic antagonists against Ralstonia solanacearum]

Cucumber bacteria wilt, caused by Ralstonia solanacearum, is one of soilborne plant diseases of worldwide origin. Biological control is considered the most environment-safe and efficacious approaches to control this disease. In this study, a total of 469 entophytic bacteria were isolated from cucumber plant roots at different growth stages and 59 of these isolates were shown antagonistic against Ralstonia solanacearum. An analysis of the level of biodiversity of the isolates at the species level was performed by comparing the Alu I restriction patterns of the 16S ribosomal DNAs (rDNAs) amplified by PCR from 59 isolates. This comparison was allowed to cluster the isolates into 5 operational taxonomic units (OTU), which were dominated by OTU1 group accounting for 39 isolates. This dominant OTU1 group was further investigated by a genomic fingerprinting technique, ERIC-PCR. The results indicated that there were 12 different ERIC-PCR types present among OTU1 groups. Isolates HE-1 and HE-2, which belonged to OTU1 and originated from all plant growth stages, were used to test the effect of biocontrol on the cucumber wilt caused be Ralstonia solanacearum. Results showed that while the growth of seedlings was promoted, the disease was suppressed too. As these strains are the same genotype, it can be hypothesized that if they were included in an inoculum, they would efficiently colonize the cucumber and protect the plant in whole growing season. Thus, the strains described here could be used in future screening programs for target biocontrol agents. The results of this study have practical importance in the context of using biocontrol agents to protect plants against rhizosphere pathogens.