Worldwide genetic variations in the sugarcane leaf scald disease pathogen, Xanthomonas albilineans

Outbreaks of leaf scald disease of sugarcane in Florida and Louisiana may have been due to the recent introduction of a distinct genetic variant of the pathogen, Xanthomonas albilineans. Two genetically distinct groups among 50 strains from Florida, one representing the original introduction (group 1) and the other (group 2) representing the more recent introduction, were detected by examining restriction fragment length polymorphism (RFLP) of DNA. Similarly, all five strains examined from Louisiana were found to belong to the second group. To analyze polymorphisms, high molecular weight DNA fragments were produced with the rare-cutting restriction enzyme, Spe 1, and separated by pulse-field gel electrophoresis. This method is presently being used to examine the genetic variability of strains from throughout the world. To date, 172 strains have been examined, and 159 of the strains can be assigned to one of four genetic groups as follows: 37 strains in group 1 from Australia, Barbados, Dominican Republic, Florida, Hawaii, Madagascar, and Mauritius; 88 strains in group 2 from Barbados, Belize, Brazil, Dominican Republic, Florida, Guadeloupe, Guyana, India, Japan, Louisiana, Martinique, Mauritius, Saint Kitts, Saint Lucia, South Africa, and Taiwan; 18 strains in group 3 from Burkina Faso, Cameroon, Ivory Coast, Malawi, Reunion, Zaire, and Zimbabwe; 19 strains in group 4 from Kenya, Madagascar, Mauritius, Reunion, South Africa, and Zimbabwe. The remaining 13 strains from Argentina, Burkina Faso, Fiji, Guadeloupe, Indonesia, Mauritius, Reunion, and Sri Lanka have not yet been assigned to existing or new groups due to their unusual RFLP patterns. The existence of genetic variants and their limited geographic distribution supports the need for programs to prevent their spread from one country to another. (Résumé d'auteur