The Biology, Genetic Diversity, and Genomics of Moniliophthora roreri, Causal Agent of Cacao Frosty Pod Rot

Theobroma cacao (cacao) is a cash crop for farmers in many countries along the equator.  Cocoa, produced from cacao beans, is the basis for the chocolate industry in the United States and the world.   One of the most devastating cacao diseases, frosty pod rot, is caused by Moniliophthora roreri.  M. roreri is found in most cacao production areas in South and Central America other than Brazil.  Recently the taxonomic identity of M. roreri was clarified and a clear relationship between M. roreri and Moniliophthora perniciosa, causal agent of witches’ broom, was established.  As part of this work, the genome of M. roreri was sequenced and its transcriptome determined.  Molecular analysis of the M. roreri/cacao interaction indicates the fungus avoids a strong defense reaction from cacao during the biotrophic phase of disease and spreads throughout the pod tissue much like an endophyte.  The cacao pod defense/stress responses intensify for at least 30 days after infection.  Eventually the pod rots, a switch to the necrotrophic phase occurs, and the pathogen rapidly sporulates.  In contrast, when M. roreri infects tolerant clones, a strong cacao defense is initiated.  M. roreri occasionally overcomes the cacao defense responses in tolerant clones and causes frosty pod rot.  When overcoming cacao tolerance numerous M. roreri genes are differentially expressed.  We are further analyzing the genetic makeup and diversity of the pathogen during infection processes and in different cacao genotypes.  The molecular interactions between Theobroma cacao and harmful microbes are complex and must be considered when developing and releasing tolerant clones for the management of frosty pod rot.