Phylogeny, taxonomy, and ecology of the North American clade of the Ceratocystis fimbriata species complex

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2004-01-01
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Johnson, Jason
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Plant Pathology and Microbiology
The Department of Plant Pathology and Microbiology and the Department of Entomology officially merged as of September 1, 2022. The new department is known as the Department of Plant Pathology, Entomology, and Microbiology (PPEM). The overall mission of the Department is to benefit society through research, teaching, and extension activities that improve pest management and prevent disease. Collectively, the Department consists of about 100 faculty, staff, and students who are engaged in research, teaching, and extension activities that are central to the mission of the College of Agriculture and Life Sciences. The Department possesses state-of-the-art research and teaching facilities in the Advanced Research and Teaching Building and in Science II. In addition, research and extension activities are performed off-campus at the Field Extension Education Laboratory, the Horticulture Station, the Agriculture Engineering/Agronomy Farm, and several Research and Demonstration Farms located around the state. Furthermore, the Department houses the Plant and Insect Diagnostic Clinic, the Iowa Soybean Research Center, the Insect Zoo, and BugGuide. Several USDA-ARS scientists are also affiliated with the Department.
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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 genotypes. Allozyme electromorphs were also 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 genotype were fully interfertile only with an aspen isolate, hickory isolates were interfertile only with other isolates of the hickory genotype, isolates from the oak genotype were only interfertile with other isolates of the oak genotype, and isolates from the cherry genotype were only interfertile with other isolates from the same genotype. Inoculation experiments showed strong host specialization by isolates from the aspen and hickory genotypes on Populus tremuloides and Carya illinoensis, but isolates from the oak and cherry genotypes inconsistently showed host specialization. Additional inoculation experiments demonstrated that Populus species differ in susceptibility to isolates of C. fimbriata from the aspen genotype. Similarly, Carya species and the related genus Juglans differed in susceptibility to hickory isolates. Morphological features distinguish isolates in the North American clade from those of the Latin American clade. The oak and aspen lineages within the North American clade are unique morphologically as well. Based on the phylogenetic evidence, interfertility, host specialization, and morphology, the oak genotype is recognized as the earlier described C. variospora, the cherry genotype as C. variospora f. pruni f. nov., the poplar genotype as C. populicola sp. nov., and the hickory genotype as C. caryae sp. nov. A new form associated with the bark beetle Scolytus quadrispinosus is described as C. caryae f. smalleyi.

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Thu Jan 01 00:00:00 UTC 2004