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Genetic Variability and Host Specialization in the Latin American Clade of Ceratocystis fimbriata

October 2003 , Volume 93 , Number  10
Pages  1,274 - 1,284

Christine J. Baker , Thomas C. Harrington , Ulrike Krauss , and Acelino C. Alfenas

First and second authors: Department of Plant Pathology, Iowa State University, Ames 50011; third author: CABI/CATIE/USDA Project, Centro Agronómico Tropical de Investigación y Enseñanza, 7170 Turrialba, Costa Rica; and fourth author: Departamento de Fitopatologia, Universidade Federal de Viçosa, Minas Gerais, Brazil

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Accepted for publication 29 April 2003.

The Ceratocystis fimbriata complex includes many undescribed species that cause wilt and canker diseases of many economically important plants. Phylogenetic analyses of DNA sequences have delineated three geographic clades within Ceratocystis fimbriata. This study examined host specialization in the Latin American clade, in which a number of lineages were identified using sequences of the internal transcribed spacer (ITS) region of the rDNA. Three host-associated lineages were identified from cacao (Theobroma cacao), sweet potato (Ipomoea batatas), and sycamore (Platanus spp.), respectively. Isolates from these three lineages showed strong host specialization in reciprocal inoculation experiments on these three hosts. Six cacao isolates from Ecuador, Trinidad, and Columbia differed genetically from other cacao isolates and were not pathogenic to cacao in inoculation tests. Further evidence of host specialization within the Latin American clade of Ceratocystis fimbriata was demonstrated in inoculation experiments in growth chambers using sweet potato, sycamore, Colocasia esculenta, coffee (Coffea arabica), and mango (Mangifera indica) plants; inoculation experiments in Brazil using Brazilian isolates from cacao, Eucalyptus spp., mango, and Gmelina arborea; and inoculation experiments in Costa Rica using Costa Rican isolates from cacao, coffee, and Xantho-soma sp. Hosts native to the Americas appeared to be colonized by only select pathogen genotypes, whereas nonnative hosts were colonized by several genotypes. We hypothesize that local populations of Ceratocystis fimbriata have specialized to different hosts; some of these populations are nascent species, and some host-specialized genotypes have been moved to new areas by humans.

Additional keywords: fungal phylogenetics, speciation.

© 2003 The American Phytopathological Society