Two Genetically Distinct Groups of Acidovorax citrulli are Present in Watermelon-growing Fields in Korea

Development of Molecular Markers for Detection of Acidovorax citrulli Strains Causing Bacterial Fruit Blotch Disease in Melon

“…The development of efficient diagnostic tools for bacterial fruit blotch-causing A. citrulli strains has been the subject of intense investigation over the past few decades. Substantial population diversity exists among strains of A. citrulli , and strains are known to show differential virulence towards various cucurbit hosts [5,23,33,45,50,61,64]. Based on this differential virulence, DNA finger-printing and biochemical properties have characterized two major groups of A. citrulli , with group II strains being predominantly isolated from watermelon hosts, while group I strains are associated with non-watermelon hosts [35].…”

“…Based on this differential virulence, DNA finger-printing and biochemical properties have characterized two major groups of A. citrulli , with group II strains being predominantly isolated from watermelon hosts, while group I strains are associated with non-watermelon hosts [35]. Each strain shows aggressive virulence to its corresponding hosts [45,65]. This defined group II strains are more virulent towards watermelon.…”

“…Most of the PCR-based A. citrulli strain-specific markers were developed by targeting specific genes, such as 16S rDNA [48], 16S-23S ITS regions of rDNA [26,28,70], YD-repeat protein [44], BOX fragments [58,67], and hrp gene sequences [71,72]. These genes are highly conserved among the members of a particular bacterial species and thus are successful in distinguishing A. citrulli strains from other bacterial species [42,45,57,58,59,60]. However, when it comes to distinguishing closely related members of the same species, for example in our case, detecting A. citrulli strains that are more virulent towards melon hosts, primers need to be designed from genomic regions that exist only in the target strains.…”

“…Polymerase chain reaction (PCR)-based assays, on the other hand, are advantageous as they offer reliable, quick, and sensitive detection of pathogenic bacterial agents. Several PCR-based assays have been successfully used for detection of A. citrulli strains, such as classical PCR; dye-based quantitative PCR, ethidium monoazide (EMA)-PCR [43], propidium monoazide (PMA)-PCR [24]), SYBR green-based real-time PCR [42,44], andenterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) [44,45]. Contrastingly, PCR assays combined with immunological techniques [46,47], immune magnetic separation (IMS) [48], and magnetic capture hybridization [49] additionally used for the detection of A. citrulli strains.…”

“…Recently, whole genome sequence of A. citrulli strains were reported in melon [50,53] and watermelon [54,55,56]. Most of the assays were developed to detect A. citrulli strains at the species level [42,45,57,58,59,60] or to distinguish model group II strain AAC00-1 (more virulent to watermelon hosts) from model group I strain M6 (more virulent to all non-watermelon cucurbit hosts) [50,61].…”