Champoiseau, P. 2002. Etude de l’épidémiologie de l’échaudure des feuilles de la canne à sucre (Saccharum spp.) causée par Xanthomonas albilineans. Master’s degree report. ISTOM - Ecole d’Ingénieur d’Agro-développement International, Cergy-Pontoise, France, 133 p.

Abstract: Albicidin production and sugarcane foliar epiphytic colonization are two major components of phytobacteria Xanthomonas albilineans. Their genetic variability was investigated within nine genes involved in toxin biosynthesis. Total genomic DNA of 172 X. albilineans strains, from 24 different geographic locations was digested by two restriction enzymes (HincII and PstI) then hybridised with pALB571 plasmid. This plasmid include nine of the 22 genes that encode the toxin biosynthesis of the strain Xa23R1 (from Florida). Eleven distinct haplotypes and two major genetic groups, named ALB-RFLP571-A and ALB-RFLP571-B, was identified. Strong correspon­dence between these two groups and the AFLP & RFLP genetic diversity groups existing within X. albilineans specie was shown. ALB-RFLP571-B group quasi exclusively include bacterial strains of the pathogen located from geographic areas where leaf scald outbreak occurred over the last 15 years. However, these strains wasn't differentiated from those of the ALB-RFLP571-A group on the basis of albicidine quantity produced in vitro. Two X. albilineans bacterial strains apparently lack the nine genes involved in albicidin biosynthesis and didn't secrete the toxin.
The foliage of two sugarcane cultivars, known to be susceptible to leaf scald disease, was inoculated under green house condition in Guadeloupe with 10 epiphytic strains of X. albiline­ans. Bacterial population density progress curve was followed up over time by droplets sampling on leaf surface. Foliar population of the pathogen was also determined by foliar grinding at the end of the experiment, three months after inoculation. X. albilineans bacterial strains was estab­lished on the foliage of the two sugarcane cultivars, but nor significant neither reproductive dif­ference was revealed between the strains.
Throughout our study, no relation was shown between the variability of the nine genes involved in albicidin biosynthesis and the variability of the two pathogenecity components of X. albilineans. Nevertheless, additional knowledge was acquired concerning the basis of ge­netic organisation of pathogeny and epiphytic survival of X. albilineans.

Key words: sugarcane, leaf scald disease, Xanthomonas albilineans, albicidin, genetic diversity, epiphytic survival, pathogeny.