Molecular Detection And Population-Genetic Diversity Of Acidovorax Avenae Subsp. Citrulli

Bacterial fruit blotch (BFB), caused by Acidovorax avenae subsp. citrulli, is a devastating disease of cantaloupe and other cucurbits.A pair of subspecies-specific primers was designed based on the hrpB gene of a known A. avenae subsp. citrulli strain AW0008 and tested for specific amplification by PCR. The primers amplified the expected fragment from all A. avenae subsp. citrulli strains and yielded no amplicons with other tested bacteria. This PCR protocol was tested for their ability to detect A. avenae subsp. citrulli in naturally diseased plant tissues, including leaves, fruits and seeds. 10²CFU of bacteria was detected by subspecies-specific primers. The PCR protocol provides a sensitive and reliable approach for routine detection and identification of A. avenae subsp. citrulli. And it is important that we can monitor whether cantaloupe is infected by A. avenae subsp. citrulli by using this method.Sixty-four A. avenae subsp. citrulli strains from cantaloupe and watermelon collected from Xinjiang, Ningxia province and America and 7 other genera bateria were analysed by genotypic typing BOX-PCR. BOX-PCR profiling amplification gave 7 clusters to 71 strains at a level of 80% similarity after dendrogram analysis. And 5 distinct groups were confirmed among 64 A. avenae subsp. citrulli strains at a level of 90% similarity after dendrogram analysis.Eighty five point nine percent of all A. avenae subsp. citrulli strains grew on nutrient plates amended with 1.25mM CuSO₄. Sixty nine point six percent of A. avenae subsp. citrulli strains collected in 2001 were insensitive to copper sulphate. In contrast, all strains collected in 2006 grew on nutrient plates amended with 1.25mM CuSO₄. It could be inferred that the prevalence of copper-insensitive strains increased. With the increasing prevalence of copper-insensitive strains, it is possible that BFB may be more difficult to manage in the future.