Molecular Characterization by RFLP-PCR of Xanthomonas axonopodis Strains, Causal Agent of Citrus Canker

摘要

Citrus canker was first reported in Argentina in 1928 and until 1980, only B canker group of strains occurred in lemons. Since 1980, the B group has been replaced by the more aggressive Asiatic canker or A group that affects all citrus species. The C group of strains, was found on Key' lime only in Brazil and the E group, occurred mainly on Swingle citrumelo in Florida citrus nurseries. Our objective was to develop a molecular procedure based on RFLP-PCR to determine the strain group of a particular isolate of X. axonopodis found in Argentine citrus. The primers were designed to amplify a 500 bp genomic sequence based on the 16S rDNA gene, the ITS region and a small fragment of 23S rDNA gene from X. axonopodis for the different strain groups (A, A" variant, B, C and E ). Subsequently, by subjecting the amplified fragment to a digestion with different restriction enzymes, the strain group could be identified. When the restriction enzyme Alul was employed,two electrophoretic profiles were observed after the digestion; one corresponding to strains of A group (including the A" variant) with three bands (75, 110 and 270 bp) and the second, including strains from B, C and E groups, with two bands (75 and 380 bp). The digestion with Sau3 gave three different patterns: one for strains from A group (inclusive of A")with two main bands of 150 and 250 bp; another with three bands of 180, 150 and 120 bp belonging to B and C groups and a third one with only one band of 400bp that included strains of E Group.