World Cocoa Foundation Research Update: March 2008
Robert D. Lumsden, Plant Pathologist and WCF Scientific Advisor
WORLD COCOA FOUNDATION: Excerpted News from AllAfrica.com http://www.allafrica.com/,
14 March 2008. Posted to the web 14 March 2008. By Ebenezer Hanson. The African Growth and Opportunity Act (AGOA) was signed into law on May 18, 2000 and offers tangible incentives for African countries to open their economies and to build free markets. It marked a fundamental shift in U.S. policy toward Africa - for the first time, the United States emphasized increased trade as a means of promoting economic development, as much as the traditional forms of development assistance. AGOA sought to increase trade by allowing qualifying sub-Saharan African countries to export most products to the United States duty-free. Besides open markets, countries need to have transparent, science-based policies and regulatory frameworks for agricultural trade consistent with international standards. Ms Constance Jackson, Associate Administrator of the United States Department of Agriculture (USDA) and leader of the mission further discussed that the US is working closely with the World Cocoa Foundation to ensure that cocoa is "grown responsibly" and with safe farm practices. She says reckoning the importance of cocoa and cocoa products to the economies of West and Central Africa, the USDA last October awarded funding to the World Cocoa Foundation under the Norman E. Borlaug International Science and Technology Fellowship Program to provide six weeks of training in the United States for seven scientists from African countries. She added that the training enhances the work of the WCF's Cocoa Improvement Programme in Ghana and other countries in West Africa. The awarding of these Fellowships is underway.
RESEARCH GROUPS: From Smilja Lambert (smilja.lambert@ap.effem.com), Mars Australia: Asisa Pacific Cocoa Breeding Group, also formalized as teh Asia Pacific Regional INGENIC Working Group, has brought together regional cocoa breeders for four years. THe collaborating cocoa breeders from national cocoa research institutions of Indonesia, India, Malaysia, Papua New Guinea, Philippines and Vietnam all agreed that cacao breeding for high yield in the presence of cocoa pod borer, Phytophthora pod rot and vascular streak disease is the regional priority. To exchange relevant planting materials between the collaborating institutions, three best crosses from each organization were defined and these hybrid seeds are now being prepared and exchanged between all collaborators. This way each one will get 15 hybrids with approx. 200 seeds each, for field planting, observation and evaluation. Hybrid seedlings will be then selected for the high yield in the presence of local pests/diseases and climate. There is a high potential that some very good planting materials will be identified. However, the big problem of this regional hybrid seed exchange was the fact that the majority of collaborating institutions do not have enough funds to establish, maintain and field-evaluate these superior cacao hybrids. Recently, the World Cocoa Foundation agreed to help the regional cocoa breeding program by allocating funding to each of the collaborating institutions (with the exception of India that kindly let others share their part) for teh establishment of field trials with these superior hybrid cocoa seedlings. This way regional breeders will be able to establish selections under the best conditions of these field trials and prepare seedlings for evaluation. However, this project will require multi-year funding for maintenance and evaluation of these hybrid seedlings in the field. This would allow the regional breeders to select good planting materilas that will be available to the regional cocoa farmers.
From Mark J. Guiltinan, Professor of Plant Molecular Biology, Department of Horticulture, Penn State University, University Park PA 16802. The following summarizes progress with the Penn State program.
Project I. Molecular Biology of Flavonoid Biosynthesis in Theobroma cacao Summary: A research project is underway to characterize the genes involved in flavonoid biosynthesis in cacao. This class of secondary metabolites is involved in pest and disease resistance, and also are key components of the "heart healthy" attributes of chocolate. Outputs of this project will be the characterization of the key genes involved in this pathway and functional analysis of their specfic roles in cacao flavonoid biosynthesis.
Progress: Six of the key genes leading to the synthesis of flavonols, proanthocyanidins and anthocyanins have been isolated and sequenced. We have determined that the majority of these are represented as single copy genes in the cacao genome. A gene encoding a transcription factor known to be the key regulatory step in activation of this pathway has also been isolated and sequenced. Each of these genes is now under analysis to verify their roles in this pathway. We are using a combination of approaches involving the model organisms Arabidopsis, tobacco and bacteria to test the enzymatic activity of each gene product to verify their putative functions. We are also using PCR gene expression assays to study the expression of these genes in different tissues, stages of development and in different cacao genotypes.
Future Impact: Practical applications of this work will be to provide tools and knowledge to better understand the basis for differences in genotypes regarding specific flavonoid components in seeds and in other plant parts. This has important implications for breeding of cacao varieties for higher levels or altered spectrums of flavonoids in seeds and potentially for disease and pest resistance. Molecular markers will be developed for use by breeders and researchers to exploit this new information.
Project II. Sequencing the Genomes of Witches’ Broom and Frosty Pod Rot. Summary: In collaboration with USDA Beltsville (B. Bailey, and L. Meinhardt) and UNICAMP, Brazil (G. Guimaraes), we are sequencing and analyzing the entire genome sequences of these two related cacao plant pathogens, which cause the majority of losses in Latin America.
Progress: At PSU, the DNA sequencing has been completed. We have sequenced 612.3 million base pairs of the monilia genome and 253.2 million base pairs of witches’ broom genome. In short, this represents a multiple fold coverage of both genomes, which enables us to predict the presence of essentially all genes of these two pathogens, and to study their structure and evolution. The annotation and analysis of this data is ongoing but has revealed interesting features and possible leads to better understand the mechanisms of fungal infection. For the witches’ broom sequence, our data has been combined with that of our Brazillian collaborators to constitute a combined sequence. We have also determined the entire mitochondrial genome sequences of both organisms.
Future Impact: This data will accelerate the study of these two pathogens and provide leads into the mechanisms of pathogenicity. These mechanisms are potential targets for efforts to reduce the damage caused by them. The study will also shed light on the evolution of these pathogens. In the long run, this knowledge will help plant breeders and pest management specialists in developing germplasm and agronomic practices to reduce the development of this disease and its spread into new cacao growing areas.
Project III. Development of a Model System to Study Witches’ Broom Disease of Cacao. Summary: Research on the interactions of cacao with witches’ broom disease are difficult at best due to a number of reasons including; difficulty in obtaining reproducible infections, difficulty in growing large number of cacao plants, lack of genomic and other basic resources, limited genetic information on cacao etc. Therefore we have developed a system to study the interactions of the S strain of witches’ broom fungus with tomato. Tomato is a model plant system with none of the limitations mentioned above. This model system will greatly speed up our progress in understanding how witches’ broom infects cacao and causes the symptoms and eventually near total loss of pods.
Progress: We have completed the development and characterization/validation of this model system. In almost every way, the symptoms of witches’ broom disease in tomato are similar to that seen in cacao. We have observed that the swelling seen in WB pathogenesis is caused primarily by increased cell division and increased cell enlargement of the vascular tissues. We have evidence that this may be caused by changes in the plant hormone auxin induced by the fungus. In collaboration with scientists at Cornell University and Nestles Tours, we have identified several regions of the tomato genome containing resistance genes for witches’ broom. We are in the process of verifying this and will begin isolation and characterization of these genes in the near future.
Future Impact: Like project 2 above, this project will contribute to increasing our knowledge of the mechanism of WB disease progress and lead to strategies to fight the disease via breeding and or agronomic practices.
Project IV. Molecular Biology of Defense Response in Cacao. Summary: Using a combination of approaches we are investigating the mechanisms by which cacao responds to pathogen infection and switches on its defense response. We have collaborated with scientists at USDA Beltsville (B. Bailey) and Miami (R. Schnell), the Smithsonian Tropical Research Station (A. Herre), and the University of Sao Paulo, Brazil (A. Figueria) in these studies. We have used several genomics approaches to identify key genes involved in defense pathway in cacao. We have developed microarrays that allow us to measure the expression of tens of thousand cacao genes in a single experiment. We have also made use of the model plant Arabidopsis to isolate and study key cacao genes involved in regulating the defense response.
Progress: A large number of genes that are implicated in the cacao defense pathway have been isolated and sequenced. We have observed the expression of these genes during interactions with pathogens and with endophytic fungi. These studies are now being extended to compare expression of these genes between different cacao genotypes. We have evidence to support the hypothesis that cacao genotypes thought to be resistant to pathogens do so by reacting quicker and to higher levels then do sensitive genotypes. We have also obtained direct evidence supporting the idea that endophytes act in part by inducing the pathways leading to thicker cell walls, thus creating a stronger barrier to fungal infection.
Future Impact: This knowledge will ultimately aid plant breeders in designing crosses aimed at stacking multiple sources of resistance against pathogens that act on different mechanisms.
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