ردیابی و شناسایی عامل بیماری گال طوقه روی درختان میوه هسته‌دار در مازندران

Bacterial root and crown gall is one of the most important diseases in nurseries, farms and gardens. In orchards under suitable conditions, a reduction in yield of up to 30% due to this disease has been reported. . The causative agent is Agrobaterium spp. belonging to the family Rhizobiaceae. The aim of this study was to identify the bacteria causing crown gall diseases on stone fruit trees in different parts of Mazandaran province. For this purpose, in 2019 from stone fruit trees including peaches, nectarines and cherries, about 120 samples with bacterial gall symptoms were collected from the orchards in eastern and centeral Mazandaran province. After transferring the samples to the laboratory, the causative agent was isolated on the general culture medium. Among the isolates, approximately 17 isolates that were creamy or milky in nutrient agar medium were identified by morphological, biochemical, physiological and molecular tests based on the presence of VirD2 and VirC genes. Pathogenicity test for the isolates was performed on tomato and carrot index plants. Based on the results of pathogenicity test, a number of isolates injected on the tomato plant caused tumors. In pathogenicity test by the carrot disc method, for the most isolates, callus symptoms appeared on the carrot discs after two to three weeks. Using VirD2A/VirD2C and VCF/VCR primer pairs, one 224 bp fragment and one 730 bp fragment were respectively amplified in a number of isolates, which confirms the presence of Ti plasmid in these isolates. The VirC sequence of one isolate had 98.57% genomic similarity with A. tumefaciens. But, the other three isolates obtained in this study had 93.28%, 93.08% and 94.78% genomic similarity to A. tumefaciens, respectively.