Biodiversity and biogeography of the cacao (Theobroma cacao) pathogen Moniliophthora roreri in tropical America

Abstract

Moniliophthora roreri, the cause of moniliasis or frosty pod rot, occurs on the neotropical rainforest genera Theobroma and Herrania. While this basidiomycete has had devastating effects on the 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/South America were analyzed. The study provided limited evidence to support the hypothesis that M. roreri is capable of sexual reproduction. The highest levels of genetic diversity occurred in Colombia and not in Ecuador as originally believed. The fungus was broadly divided into five genetic groups. Two of these have a wide geographic range: Bolívar group (north of Santander in Colombia, eastern Venezuela, peripheral Ecuador, Peru), and Co-West group (western Colombia, central Ecuador, 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 represent the centre of origin for M. roreri. Sequence data from the internal transcribed spacer region of the nuclear rDNA repeat were congruent with the AFLP/ISSR results, dividing M. roreri into two broad groups: 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. The spread of M. roreri into new areas and countries mediated by human activity is discussed.