نخستین گزارش از عوامل باکتریایی مولد پوسیدگی های پس از برداشت چغندرقند در ایران

Sugar beet (Beta vulgaris) is an industrial plant belonging to the Chenopodiacae family that is cultivated as a source of sugar. Soft and dry rot of sugar beet tap due to bacterial agents is one of the reducing factors of quantity and quality of sugar beet crop, which despite high prevalencing in Iran, has not received much attention. Roots with advanced soft rot symptoms had a vinegar-like fermented smell, rotted out cavities, and viscous slime indicative of bacterial activity. In dry rot, dry spots on the roots that extend to its depth; it is without any slime and occurs in conditions with less moisture. In this study, samples with signs of root rot were collected from silos and sugar beet fields located in Isfahan, Kermanshah, Khuzestan and West Azerbaijan provinces in 2016-2017. Pieces of Borders between rot root and healthy tissues were prepared and after superficial disinfection by sodium hypochlorite was completely crushed in sterile distilled water. Suspension was cultured linearly on EMB and NA medium and stored at 28 °C. In total, 48 bacterial isolates were isolated from infected tissues. To prove the pathogenicity, disks of healthy sugar beet roots were prepared in size, 2.5-3 cm × 0.7 cm. After surface disinfection, the disks were transferred to sterile petries containing wet filter paper and drilled central cavities in disks. 30 µl of suspension of each isolate (concentration ̴108 CFU ml -1) was inoculated to it. The petri dishes were incubated at 30-32 ° C for one week. Finally, three pathogenic isolates that caused the most rotted were selected. Molecular identification was performed by amplification of 16S rRNA gene using Fd2 and Rp1 primers and followed by nucleotide sequencing and comparison with similar sequences in NCBI. Phylogenetic analysis showed that Isf19 and Kh2 isolates, causing sugar beet soft rot agents, had the most nucleotide similarity to Bacillus pumilus and Enterobacter roggenkampii (99.86% and 99.36% nucleotide similarity, respectively). In addition, the results showed that Buk12, causing sugar beet dry rot agent, had the 99.79% nucleotide similarity to Pseudomonas thivervalensis. Although the bacteria have been reported in other studies as causes of soft rot in other hosts, the present study is the first report of soft rot in sugar beet.