Ceratocystis fimbriata is a large, diverse complex of species that cause wilt-type diseases of many economically important plants. Previous studies have shown that isolates in three monophyletic lineages within the Latin American clade of C. fimbriata are host-specialized to cacao (Theobroma cacao), sweet potato (Ipomoea batatas) and sycamore (Platanus spp.), respectively. We paired testers of opposite mating type from isolates of these lineages to find intersterility groups. Two intersterility groups corresponded to the sweet potato and sycamore lineages, respectively. The cacao lineage contained two intersterility groups, corresponding to two genetic sublineages centered in western Ecuador and Brazil/Costa Rica/Colombia. Six isolates from cacao that were not members of the cacao lineage and were not pathogenic to cacao in an earlier study also were intersterile with members of the two cacao intersterility groups. Some pairings between testers from different lineages or sublineages yielded perithecia from which a few abnormal progeny could be recovered, typical of interspecific hybrids. These progeny showed abnormal segregation of the MAT-2 gene and mycelial morphology, showing that they were indeed the result of crosses. Isolates of the sweet potato, cacao, and sycamore lineages were indistinguishable morphologically except for the presence or absence of a doliform (barrel-shaped) conidial state and minor differences in size of perithecial bases and necks and ascospores. C. fimbriata originally was described from sweet potato. We describe the cacao pathogen as a new species, Ceratocystis cacaofunesta and we raise the sycamore pathogen from a form to species Ceratocystis platani.

The plant pathogenic fungus Ceratocystis fimbriata f. platani attacks Platanus species (London plane, oriental plane and American sycamore) and has killed tens of thousands of plantation trees and street trees in the eastern United States, southern Europe and Modesto, California. Nuclear and mitochondrial DNA fingerprints and alleles of eight polymorphic microsatellite markers of isolates of C. fimbriata from these regions delineated major differences in gene diversities. The 33 isolates from the eastern United States had a moderate degree of gene diversity, and unique genotypes were found at each of seven collection sites. Fingerprints of 27 isolates from 21 collection sites in southern Europe were identical with each other; microsatellite markers were monomorphic within the European population, except that three isolates differed at one locus each, due perhaps to recent mutations. The genetic variability of C. fimbriata f. platani in the eastern United States suggests that the fungus is indigenous to this region. The genetic homogeneity of the fungus in Europe suggests that this population has gone through a recent genetic bottleneck, perhaps from the introduction of a single genotype. This supports the hypothesis that the pathogen was introduced to Europe through Naples, Italy during World War II on infected crating material from the eastern United States. The Californian population may also have resulted from introduction of one or a few related genotypes because it, too, had a single nuclear and mitochondrial genotype and limited variation in microsatellite alleles.

Ceratocystis fimbriata is a widely distributed, plant pathogenic fungus that causes wilts and cankers on many woody hosts. Earlier phylogenetic analyses of DNA sequences revealed three geographic clades within the C. fimbriata complex that are centered respectively in North America, Latin America and Asia. This study looked for cryptic species within the North American clade. The internal transcribed spacer regions (ITS) of the rDNA were sequenced, and phylogenetic analysis indicated that most isolates from the North American clade group into four host-associated lineages, referred to as the aspen, hickory, oak and cherry lineages, which were isolated primarily from wounds or diseased trees of Populus, Carya, Quercus and Prunus, respectively. A single isolate collected from P. serotina in Wisconsin had a unique ITS sequence. Allozyme electromorphs also were highly polymorphic within the North American clade, and the inferred phylogenies from these data were congruent with the ITS-rDNA analyses. In pairing experiments isolates from the aspen, hickory, oak and cherry lineages were interfertile only with other isolates from their respective lineages. Inoculation experiments with isolates of the four host-associated groupings showed strong host specialization by isolates from the aspen and hickory lineages on Populus tremuloides and Carya illinoensis, respectively, but isolates from the oak and cherry lineages did not consistently reveal host specialization. Morphological features distinguish isolates in the North American clade from those of the Latin American clade (including C. fimbriata sensu stricto). Based on the phylogenetic evidence, interfertility, host specialization and morphology, the oak and cherry lineages are recognized as the earlier described C. variospora, the poplar lineage as C. populicola sp. nov., and the hickory lineage as C. caryae sp. nov. A new species associated with the bark beetle Scolytus quadrispinosus on Carya is closely related to C. caryae and is described as C. smalleyi.

Ceratocystis fimbriata is a serious fungal pathogen on a wide range of plants, but many cryptic species within C. fimbriata are apparently host‐specialized. Anchor polymerase chain reaction (PCR) and simple sequence repeat (SSR) enriched libraries were used to develop 16 microsatellite markers for C. fimbriata. All markers were polymorphic when tested against isolates from four host‐specialized lineages of the pathogen. These markers will be valuable for phylogenetic and population genetic studies, as well as for tracking accidental introductions of host‐specialized forms of the pathogen.

Ceratocystis cacaofunesta ( = Ceratocystis fimbriata ) causes a lethal wilt disease of cacao ( Theobroma cacao ) in Latin America. Polymorphic microsatellite markers, (CAT) 5 nuclear DNA fingerprints and Hae III mitochondrial DNA fingerprints were used to compare genetic diversity among isolates of C. cacaofunesta collected from populations in western Ecuador, Costa Rica, Colombia, and Rondônia and Bahia in Brazil. Microsatellite markers and nuclear DNA fingerprints separated Ecuadorian isolates from isolates of the other four populations, and these two major groups correspond to genetic lineages already identified from ITS-rDNA sequences and intersterility groupings. Mitochondrial DNA fingerprints also demonstrated substantial diversity and split the Ecuadorian isolates into two groups. All marker types showed limited variation in the Colombian, Costa Rican and Bahian populations, as might be expected for introduced populations that have gone through recent genetic bottlenecks. In contrast, the Rondonian and western Ecuadorian populations showed gene diversity values similar to natural populations of other Ceratocystis species. The Rondonian population was the only sampled population in the native range of T. cacao (the Upper Amazon), and the putatively introduced populations were more closely related to the Rondonian population than to the western Ecuadorian population. The Ecuadorian population is in an area with other native Theobroma species, which may serve as natural hosts.