Abstract
Sugar beet crown gall is a bacterial disease caused by Agrobacterium tumefaciens remains one of the most severe diseases, which cause unlimited loss of crop in Egypt and over world. A. tumefaciens pathogen was isolated from Sugar beet infected plants and molecularly characterized by 16S rDNA sequence and Koch's postulates applied to assure the crown gall disease that causes high defects in the sugar beet yield. The pathogens' DNA was isolated, and the PCR technique based on 16S RNA was used for three isolates. The results of comparative sequencing analysis of the new races showed high identity between races YH2 and YH3, while there was high similarity between both of YH2, 3 and YH1. A phylogenetic tree was generated based on the genomic sequences of different Agrobacterium species. The genomic sequences of YH1 share close homology with the genome sequences of Agrobacterium tumefaciens. While the genome sequences of YH2 and YH3 showed high homologues to Agrobacterium rhizogenes, this data revealed that the genomic sequences of YH2 share close homology with the genome sequences of YH3, and both of them are high homologues to A. rhizogenes. While the genome sequence of YH1 is similar to both of YH2, 3 and high homologues to Agrobacterium tumefaciens. This finding reflected that the similarity of genomic sequences and conserved regions among the new races is evolutionarily conserved in the genus of Agrobacterium. Effectiveness of antimicrobial compounds on A. tumefaciens was studied In Vitro. The inhibitory effect of Bacillus subtilis on A. tumefaciens was the highest inhibition zone diameter that was recorded among all of the antimicrobial compounds that were used in the experiment in vitro. Moreover, the antibiotic streptomycin, plant extract from Hibiscus sabdariffa, Rhus sp. pomegranate peel, and nano silver have high effects on bacterial growth compared to control.