A Complex Population Structure of the Cassava Pathogen Xanthomonas axonopodis pv. manihotis in Recent Years in the Caribbean Region of Colombia

Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis (Xam), is the most important bacterial disease affecting this crop. A continuous surveillance of the pathogen population dynamics is required to develop an efficient disease management program. During the 1990s, Xam populations showed high levels of genetic variation and relevant migratory processes that were important determinants of the distribution of the pathogen diversity in Colombia. Aiming to characterize the current population structure of the pathogen and the evolutionary forces that shape these populations, sampling collections were carried out from September 2008 until November 2010 in the Colombian Caribbean Region. One hundred and sixty bacterial isolates were characterized using amplified fragment length polymorphism (AFLP) markers. Additionally, a subset of effector genes were sequenced in some isolates to determine their usefulness in Xam population studies and to provide additional information to that obtained with AFLPs. Virulence patterns of ten isolates were determined in nine cassava accessions. Our results show a complex architecture of population and confirm migratory process previously reported in the Caribbean Region. Chinú, one of the locations sampled, presented remarkable features in population dynamics such as longer genetic distances, higher diversity indices, and a genetically differentiated population when it was compared with other locations. Virulence tests showed that MCOL2215, one of the most cultivated cassava varieties in the Caribbean coast, was susceptible to the majority of Xam isolates tested. This study shows the current condition of populations of Xam in the Caribbean Region of Colombia, and it contributes to improve the existing bacterial blight control practices.