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Title: Biodiversity and biogeography of the cacao (Theobroma cacao L.) pathogen Moniliophthora roreri in tropical America

Author
item PHILLIPS-MORA, W. - COSTA RICA
item Aime, Mary
item WILKINSON, M. - COSTA RICA

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2007
Publication Date: 12/20/2007
Citation: Phillips-Mora, W., Aime, M.C., Wilkinson, M.J. 2007. Biodiversity and biogeography of the cacao (Theobroma cacao L.) pathogen Moniliophthora roreri in tropical America. Plant Pathology. 56:911-922.

Interpretive Summary: Cocoa is a tropical tree crop that forms the basis for a multibillion dollar chocolate industry in the United States and elsewhere. A devastating disease known as frosty pod rot has caused a serious decline in cocoa production in tropical America. This disease is caused by a fungus, however, little is known about the how this species is distributed and how variable are its populations. Using molecular characterization this research demonstrated that there are five different groups of this fungus each differing in geographic distribution. In addition these populations vary in how genetically diverse they are. Based on these data it is concluded that this disease has been the spread into new areas and countries by human activity. Plant breeders and plant pathologists will use this research to stop the spread of this disease that threatens the U.S. chocolate industry.

Technical Abstract: Moniliophthora roreri is the causal agent of frosty pod rot, which occurs on the neotropical rainforest genera Theobroma and Herrania. While this basidiomycete has had devastating effects on the commercially important cacao tree (T. cacao) in tropical America, where it is confined, little is known of its biogeography and intraspecific genetic variability. Here, AFLP and ISSR profiles of 94 isolates of M. roreri from across its geographic range in Central and South America were obtained and analyzed. Although considerable genetic variation was found, regions of comparative genetic uniformity were also identified. The study provided limited evidence to support the hypothesis that M. roreri is capable of sexual reproduction. The highest levels of genetic diversity are found in Central/north-eastern Colombia and not in Ecuador as originally believed. M. roreri can be broadly divided into five genetic groups based on the AFLP and ISSR data. Two of these have a wide geographic range: Bolívar group (north of Santander in Colombia, eastern Venezuela, peripheral Ecuador and Peru), and Co-West group (western Colombia, central Ecuador and Central America). The other groups are all apparently endemic to Colombia (Co-East and Co-Central groups) or north-western Ecuador (Gileri group). We speculate that central/north-eastern Colombia may also represent the centre of origin for M. roreri. Sequence data from the internal transcribed spacer region of the nuclear rDNA repeat were also analyzed for the same isolates and found to be congruent with the AFLP/ISSR results, dividing M. roreri into two broad groups: one, which we term the Orientalis group, comprising most isolates from the Co-East, Co-Central and Bolívar groups, and the Occidentalis group, comprising isolates from the Co-West and Gileri groups. We conclude that the spread of M. roreri into new areas and countries has been mediated by human activity.