Genetic diversity and interfertility among highly differentiated populations of Ceratocystis fimbriata in Brazil

Mating studies showed that isolates of the insect-associated wilt pathogen Ceratocystis fimbriata from Eucalyptus spp., mango, fig, inhame (Colocasia esculenta), Gmelina arborea and sweet potato were interfertile, and progeny from those crosses showed normal segregation for microsatellite markers. Genetic diversity was compared among 13 populations of C. fimbriata collected from six states in Brazil using 15 highly polymorphic microsatellite markers. The gene diversity values of most eucalyptus and mango populations from Minas Gerais, Bahia, Rio de Janeiro and São Paulo states were similar to putatively native populations of Ceratocystis platani and C. cacaofunesta, two other species in the C. fimbriata complex that are homothallic. Index of association values indicated substantial asexual reproduction or selfing in populations on mango and eucalyptus. Most of these eucalyptus and mango populations were not highly differentiated from each other, and these populations and genotypes appeared to be more closely related to each other than to other populations by UPGMA analyses. By contrast, the G. arborea population from Pará and the fig and inhame populations from São Paulo had relatively low levels of diversity and were highly differentiated from each other and all other studied populations, suggesting that they were from different origins and had gone through genetic bottlenecks. One of the eucalyptus populations in Bahia consisted of a single genotype and may have been introduced to the site in infected cuttings from another Bahia location. Similarly, a mango population from Mato Grosso do Sul consisted of a single genotype, which was identical to one of the genotypes found on mango in São Paulo. Aside from introductions by humans, mating studies and genetic analyses suggest that limited dispersal distance and a high degree of selfing or asexual reproduction lead to local populations of C. fimbriata that have limited diversity but are highly differentiated from other populations.