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Title: THE CAUSAL AGENTS OF WITCHES¿ BROOM AND FROSTY POD ROT OF COCOA (THEOBROMA CACAO) FORM A NEW LINEAGE OF MARASMIACEAE

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

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2005
Publication Date: 3/7/2006
Citation: Aime, M.C., Phillips-Mora, W. 2006. The causal agents of witches broom and frosty pod rot of cocoa (chocolate, Theobroma cacao) form a new lineage of Marasmiaceae. Mycologia. 97(5):1012-1022.

Interpretive Summary: Cocoa is a tropical tree crop that forms the basis for the multibillion dollar chocolate industry in the United States and elsewhere. Two devastating fungal diseases have caused the recent plummet of cocoa production in tropical America. These diseases are known as witches' broom and frosty pod rot. Despite their importance, relatively little is known about either of the fungi that cause these diseases. One fungus produces a mushroom fruiting body while the other develops only a thin coating of spores on the cocoa fruit. By analyzing and comparing genomic data, the relatedness of these two fungal pathogens to each other and their placement in the fungal 'family tree' was determined. This research proves that, despite their very different outward appearances, these two pathogens of cocoa are closely related to each other and are placed in the same genus. This research has important implications for cocoa breeding programs and for efforts to fight the diseases. Because these two disease-causing fungi are closely related, it will be possible to breed for resistance to both diseases. Importantly, disease control measures that are currently controlling witches' broom may also be effective against frosty pod rot. Plant breeders and plant pathologists will use this research to develop effective control measures for these serious diseases of cocoa that threaten the U.S. chocolate industry.

Technical Abstract: The two most devastating diseases of cocoa (Theobroma cacao) in tropical America are caused by the fungi Crinipellis perniciosa (witches' broom disease) and Moniliophthora roreri (frosty pod rot or moniliasis disease). Despite the agricultural, socio-economic, and environmental impact of these fungi, most aspects of their life cycles are unknown, and the phylogenetic relationships of M. roreri have yet to be conclusively established. In this paper, extensive phylogenetic analyses of five nuclear gene regions confirm that C. perniciosa and M. roreri are sister taxa that belong in the Marasmiaceae (euagarics). Furthermore, these taxa form part of a separate and distinct lineage within the family. This lineage includes the biotrophic fungi Moniliophthora perniciosa comb. nov. and M. roreri, as well as one undescribed endophytic species. The sister genera to Moniliophthora are Marasmius, Crinipellis, and Chaetocalathus, which consist mainly of saprotrophic litter fungi.