Applying SNP marker technology in the cacao breeding programme in Ghana (original) (raw)
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The development of a novel SNP genotyping assay to differentiate cacao clones
Scientific Reports, 2019
In this study, a double-mismatch allele-specific (DMAS) qPCR SNP genotyping method has been designed, tested and validated specifically for cacao, using 65 well annotated international cacao reference accessions retrieved from the Center for Forestry Research and Technology Transfer (CEFORTT) and the International Cocoa Quarantine Centre (ICQC). In total, 42 DMAS-qPCR SNP genotyping assays have been validated, with a 98.05% overall efficiency in calling the correct genotype. In addition, the test allowed for the identification of 15.38% off-types and two duplicates, highlighting the problem of mislabeling in cacao collections and the need for conclusive genotyping assays. The developed method showed on average a high genetic diversity (He = 0.416) and information index (I = 0.601), making it applicable to assess intra-population variation. Furthermore, only the 13 most informative markers were needed to achieve maximum differentiation. This simple, effective method provides robust a...
2014
Accurate identification of individual genotypes is important for cacao ( Theobroma cacao L.) breeding, germplasm conservation and seed propagation. The development of single nucleotide polymorphism (SNP) markers in cacao offers an effective way to use a high-throughput genotyping system for cacao genotype verification. In the present study, high-throughput genotyping with SNP markers was used to fingerprint 160 cacao trees in the germplasm collection at the Cocoa Research Institute of Ghana (CRIG). These accessions had been originally introduced from international germplasm collections. The multilocus SNP profiles, generated by the Sequenom Mass Spectrometry platform, were compared with the SNP profiles of reference trees maintained in the international cacao collections. The comparison unambiguously identified mislabeled trees. For materials introduced as hybrid seeds without an available reference genotype, parentage analysis and model-based assignment were applied to verify their...
The impact of SNP fingerprinting and parentage analysis in varietal identification in cacao
Tree Genetics & Genomes
Evidence for the impact of mislabeling and/or pollen contamination on consistency of field performance has been lacking to reinforce the need for strict adherence to quality control protocols in cacao seed garden and germplasm plot management. The present study used SNP fingerprinting at 64 loci to examine the diversity, labeling errors and parentage in 2551 trees obtained from six seed gardens, breeders clone collection and single-cross progenies and a sample of farmers' trees in Ghana. Clone mislabeling was pervasive, both within the seed garden clones and among clones of the breeders' active collection. Among the seed garden clones, mislabeled trees were assigned to other parental clones used in the seed garden, pointing to labeling errors prior to planting as the principal cause of mislabeling. Among the breeders' clone collection, both homonymous and synonymous mislabeling were identified in addition to trees with unique genotypes. This implicates pre-planting labeling errors and rootstocks overtaking budded scions. Parentage analysis supported the Amelonado ancestry of farmers' varieties but with significant contribution of Upper Amazon introductions. Parentage of recently developed clones and of progenies of controlled crosses showed evidence of both pollen contamination and effects of mislabeled parents. The observed patterns of unexpected parentage had direct effects on the consistency of the variety performance between trials and increased within-plot variability for families with mixed ancestry. The results provide a strong basis for mainstreaming SNP fingerprinting in cacao breeding programs to improve the efficiency of the variety development process.
Tree Genetics & Genomes, 2015
Evidence for the impact of mislabeling and/or pollen contamination on consistency of field performance has been lacking to reinforce the need for strict adherence to quality control protocols in cacao seed garden and germplasm plot management. The present study used SNP fingerprinting at 64 loci to examine the diversity, labeling errors and parentage in 2551 trees obtained from six seed gardens, breeders clone collection and single-cross progenies and a sample of farmers' trees in Ghana. Clone mislabeling was pervasive, both within the seed garden clones and among clones of the breeders' active collection. Among the seed garden clones, mislabeled trees were assigned to other parental clones used in the seed garden, pointing to labeling errors prior to planting as the principal cause of mislabeling. Among the breeders' clone collection, both homonymous and synonymous mislabeling were identified in addition to trees with unique genotypes. This implicates pre-planting labeling errors and rootstocks overtaking budded scions. Parentage analysis supported the Amelonado ancestry of farmers' varieties but with significant contribution of Upper Amazon introductions. Parentage of recently developed clones and of progenies of controlled crosses showed evidence of both pollen contamination and effects of mislabeled parents. The observed patterns of unexpected parentage had direct effects on the consistency of the variety performance between trials and increased within-plot variability for families with mixed ancestry. The results provide a strong basis for mainstreaming SNP fingerprinting in cacao breeding programs to improve the efficiency of the variety development process.
Livingston et al.- SNPs in cacao
Single nucleotide polymorphism (SNP) markers are increasingly being used in crop breeding programs, slowly replacing simple sequence repeats (SSR) and other markers. SNPs provide many benefits over SSRs, including ease of analysis and unambiguous results across various platforms. We have identified and mapped SNP markers in the tropical tree crop Theobroma cacao, and here we compare SNPs to SSRs for the purpose of determining off-types in clonal collections. Clones are used as parents in breeding programs and the presence of mislabeled clones (off-types) can lead to the propagation of undesired traits and limit genetic gain from selection. Screening was performed on 186 trees representing 19 Theobroma cacao clones from the Institute of Agricultural Research for Development (IRAD) breeding program in Cameroon. Our objectives were to determine the correct clone genotypes and off-types using both SSR and SNP markers. SSR markers that amplify 11 highly polymorphic loci from six linkage groups and 13 SNP markers that amplify eight loci from seven linkage groups were used to genotype the 186 trees and the results from the two different marker types were compared. The SNP assay identified 98% of the off-types found via SSR screening. SNP markers spread across multiple linkage groups may serve as a more cost-effective and reliable method for off-type identification, especially in cacao-producing countries where the equipment necessary for SSR analysis may not be available.
Breeding Science
The international cacao collection in CATIE, Costa Rica contains nearly 1200 accessions of cacao, mainly from the center of genetic diversity of this species. Among these accessions, the United Fruit clones (UF clones) were developed by the United Fruit Company in Costa Rica, and they represent one of the earliest groups of improved cacao germplasm in the world. Some of these UF clones have been used as key progenitors for breeding resistance/tolerance to Frosty Pod and Black Pod diseases in the Americas. Accurate information on the identity and background of these clones is important for their effective use in breeding. Using Single Nucleotide Polymorphism (SNP) markers, we genotyped 273 cacao germplasm accessions including 44 UF clones and 229 reference accessions. We verified the true-to-type identity of UF clones in the CATIE cacao collection and analyzed their population memberships using maximum-likelihood-based approaches. Three duplicate groups, representing approximately 30% of the UF clones, were identified. Both distance-and model-based clustering methods showed that the UF clones were mainly composed of Trinitario, ancient Nacional and hybrids between ancient Nacional and Amelonado. This result filled the information gap about the UF clones thus will improve their utilization for cacao breeding.
Plant Genetic Resources, 2012
Elucidation of genetic identity and population structure of cacao germplasm within an international cacao genebank. Abstract Theobroma cacao L., or cacao, is the source of cocoa products used in the making of chocolate. These tropical trees are conserved in living genebanks. The International Cocoa Genebank, Trinidad is one of the largest ex situ collections in the public domain. Mislabelling is a critical problem and the correction of this problem is vital to improve the accuracy and efficiency of genebank management. Using microsatellite DNA markers, we assessed the level of mislabelling in a group of Refractario cacao that originated from Ecuador and determined their population memberships through Bayesian clustering analysis. The microsatellite data revealed a synonymous rate of 7.5% and an error rate of 39.4% in this germplasm subset. The analysis of the population structure grouped the Refractario accessions into four subclusters, indicating intra-population heterogeneity in this germplasm group. Based on the results, we recommend that when the assignment test is used for cacao genotype identification, it should (a) use duplicated samples as internal checks, (b) choose suitable reference accessions, including a known homogeneous group and (c) employ subclustering checks to obtain reliable results. The information framework generated is discussed in relation to the management of the collection, population enhancement and future research of the collection.
2018
POKOU N. Desire., Tahi G. Mathias., Guiraud B. Brigitte., Ranjana Bhattacharjee., Motamayor Juan Carlos 1Centre National de recherche Agronomique (CNRA), 01 BP 1740 Abidjan 01 2International Institute of Tropical Agriculture (IITA) PMB 5320, Ibadan, Nigeria. 3MARS-Inc, C/o United States Department of Agriculture /Agricultural Research Service (USDAARS).13601 Old Cutler Road, Miami, Florida, USA.
Molecular characterization of an international cacao collection using microsatellite markers
Tree Genetics & Genomes, 2009
Plant germplasm collections invariably contain varying levels of genetic redundancy, which hinders the efficient conservation and utilization of plant germplasm. Reduction of genetic redundancies is an essential step to improve the accuracy and efficiency of genebank management. The present study targeted the assessment of genetic redundancy and genetic structure in an international cacao (Theobroma cacao L.) collection maintained in Costa Rica. A total of 688 cacao accessions maintained in this collection were genotyped with 15 simple sequence repeat (SSR) loci, using a capillary electrophoresis genotyping system. The SSR markers provided a high resolution among the accessions. Thirty-six synonymously labeled sets, involving 135 accessions were identified based on the matching of multilocus SSR profiles. After the elimination of synonymous sets, the level of redundancy caused by closely related accessions in the collection was assessed using a simulated sampling scheme that compared allelic diversity in different sample sizes. The result of the simulation suggested that a random sample of 113 accessions could capture 90% of the total allelic diversity in this collection. Principal Coordinate Analysis revealed that the Trinitario hybrids from Costa Rica shared a high similarity among groups as well as among individual accessions. The analysis of the genetic structure illustrated that the within-country/within-region difference accounted for 84.6% of the total molecular variation whereas the among-country/among-region difference accounted for 15.4%. The Brazilian germplasm contributed most to this collection in terms of total alleles and private alleles. The intercountry/interregion relationship by cluster analysis largely agreed with the geographical origin of each germplasm group and supported the hypothesis that the Upper Amazon region is the center of diversity for cacao. The results of the present study indicated that the CATIE International Cacao Collection contains a high level of genetic redundancy. It should be possible to rationalize this collection by reducing redundancy and ensuring optimal representation of the genetic diversity from distinct germplasm groups. The results also demonstrated that SSR markers, together with the statistical tools for individual identification and redundancy assessment, are technically practical and sufficiently informative to assist the management of a tropical plant germplasm collection.