Host specialization, intersterility, and taxonomy of populations of Ceratocystis fimbriata from sweet potato, sycamore, and cacao
Ceratocystis fimbriata is a large complex of fungal species that cause wilt-type diseases on a variety of temperate and tropical plants. Within the Latin American clade of C. fimbriata, isolates from sweet potato (Ipomoea batatas), sycamore ( Platanus spp.), and cacao (Theobroma cacao) form monophyletic lineages and are specialized to these three hosts. The sweet potato and sycamore lineages correspond to intersterility groups, and there are two intersterility groups within the cacao lineage, corresponding to a sublineage in western Ecuador and a second sublineage in Brazil, Colombia, and Costa Rica. The cacao lineage is described as a new species, C. cacaofunesta, and the sycamore lineage is raised from a form to a species, C. platani. Genetic analyses of progeny from crosses within and between C. fimbriata, C. cacaofunesta, and C. platani showed that these species likely have different numbers, sizes, or rearrangements of chromosomes. A population genetics study of C. platani using polymorphic microsatellite markers and nuclear and mitochondrial DNA fingerprints revealed that the population in the eastern USA is probably indigenous, and the pathogen was introduced to southern Europe and Modesto, California. A study of C. cacaofunesta using the same markers revealed that the populations of this pathogen in Ecuador and Rondonia (in the Upper Amazon of Brazil) are likely to be indigenous, while populations in Bahia Brazil, Colombia, and Costa Rica resulted from introductions of an Upper Amazonian population.