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Genetic diversity of the cocoa pathogen, Moniliophthora roreri, and its relationship within Basidiomycetes

Funders

United States Department of Agriculture (USDA)

Partners

University of Reading and CATIE

Project Description


Cocoa pod with Moniliophthora roreri

Problem/Issue. Moniliophthora pod rot caused by Moniliophthora roreri is a destructive disease, currently confined to tropical America where it causes over 60% loss of the crop in some areas. Its rapid dissemination in Ecuador from 1919 caused the abandonment of millions of trees and an 80% reduction in cocoa yield between 1914 and 1933. Similar levels of damage have been reported in other countries, such as Costa Rica, as the fungus spread further. The fungus covers the pod with a white mycelial mat of spores and gives it a frosted appearance, hence its alternative common name of 'frosty pod rot'. The disease is currently estimated to cause 5% of the total global loss of cocoa, but because of its ability to spread rapidly (through masses of airborne spores), there is now great concern that it will spread to other cocoa-growing countries in tropical America, e.g. Brazil. Spread of the disease to the other major cocoa-growing areas around the world has also become more likely because of increased movement of people and commodities. This is an alarming prospect, given the pathogen's aggressiveness and the apparent susceptibility of most of the genotypes grown world-wide.

Measures to Date. Some cultural practices have been demonstrated to be effective, but demand much effort and continuity by the farmers. The use of conventional chemical (copper) fungicides has failed to halt the progress of this disease in South and Central America, and thus alternative strategies are proposed (these are described in other CABI Bioscience projects on this website), including biological control, improved application of chemical and biological agents, and breeding for resistance. The use of resistant cocoa genotypes could become the basis of more practical, long term disease control. However, for this to be successful, knowledge of specific aspects of the fungus' biology, such as its level of genetic diversity and the sources of this variability, is required. At present, information on genetic variability in M. roreri is very scant.

Project Activities. The general objective of this research is to establish the level of genetic variation of M. roreri and to determine the possible sources of variation at the molecular, morphological, physiological, and pathogenic levels. This information will be a basis for more effective genetic improvement programmes, define more efficient control strategies, determine better strategies to avoid fungal dissemination to other regions or countries, and facilitate more detailed study of the host-pathogen relationship. Also, a more detailed knowledge of the phylogenetic relationship between M. roreri and other basidiomycetes could contribute to a rational transfer of information to a less well studied fungus. The project will draw on CABI Bioscience's long history and considerable expertise in studying this pathogen.

Achievements So Far

A collection of isolates of the pathogen was made throughout Central and South America where the disease is known to occur. A preliminary morphological comparison of these isolates was made and 95 isolates were then analysed using different molecular techniques such as Amplification Fragment Length Polymorphism (AFLPs), Inter Sequence Repeat (ISSRs), Polymerase Chain Reaction (PCR), Internal Transcribed Spacer (ITS) region and mitochondrial DNA analysis in an attempt to determine the genetic diversity and geographic distribution of M. roreri in Central and South America.

What Next

Comparative morphological studies will be continued in Costa Rica during the second year of the project. Further isolates may be obtained in an effort to further study the genetic diversity of the pathogen in Latin America. Also, the development of rapid screen for resistance are planned as is the screening of CATIE germplasm using isolates from Costa Rica.

(Co-ordinators)
Dr.Julie Flood j.flood@cabi.org
Dr. Harry Evans h.evans@cabi.org
Dr. Ulrike Krauss ukrauss@catie.ac.cr

Mr. Wilbert Phillips wphillip@catie.ac.cr

Start date: October 1999

End date: Ongoing

 

 
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Contact CABI Commodities:
CABI Commodities Coffee Co-ordinator - Dr. Peter Baker - p.baker@cabi.org
CABI Commodities Cocoa Co-ordinator - Dr. Keith Holmes - k.holmes@cabi.org
CABI Commodities Project Administrator - cabi-commodities@cabi.org