Biodiversity, epidemiology and virulence of Colletotrichum gloeosporioides. I. Genetic and pathogenic diversity in Colletotrichum gloeosporioides isolates from Stylosanthes guianensis

Anthracnose, caused by Colletotrichum gloeosporioides, is the most important and widespread disease of Stylosanthes, a diverse tropical and subtropical forage legume naturally distributed in central and South America. This paper compares the genetic and pathogenic diversity of 45 isolates, which originated from S. guianensis genotypes. Published information on the pathogenic diversity of these isolates on a set of 12 S. guianensis was used. The amount of genetic diversity was measured at molecular level by polymerase chain reaction amplifications of DNA with 9 arbitrary primers of 10 bases each using the Random Amplified Polymorphic DNA (RAPD) markers. The amplifications revealed scorable polymorphism among the isolates, and a total of 80 band positions were scored. Using Ward's method (N = 6) of statistical analysis, the isolates were separated into 6 clusters. Generally, isolates were clustered together by their geographic origin and/or their original host genotype. Isolates from Carimagua, Colombia, a savanna ecosystem and a long-time Stylosanthes breeding and selection site, exhibited a relatively wider range of genetic diversity than those from a newly opened trial site in the Amazon basin of Colombia. No strict correlation existed between genetic diversity, as measured by RAPD, and differential virulence, as defined by the pathotype. Isolates of the same pathotype/RAPD grouping often originated from the same host genotype and/or geographical locality. This information will be useful in determining future sampling strategies for the pathogen population.