Cacao Genetic Resources Conservation and Utilization for Sustainable Production in Nigeria

Theobroma cacao, the source of chocolate, is one of the most important tree-crop that serves the purpose of sustaining the economy of millions of households and the largest non-oil foreign exchange earnings in Nigeria. The management of cacao genetic resources as it affects sustainable production of cocoa in Nigeria is reviewed. These include details of the diversity present in the germplasm collections, their utilization in varietal development and current status of the field genebanks as revealed by DNA fingerprinting using single nucleotide polymorphisms (SNPs) markers. Factors contributing to continuing backlash in the annual outputs of cocoa in Nigeria are also highlighted. The prospects of advances in the science of cacao genomics for up-scaling production and its impacts on the improvement of the industry in the country are discussed

Population Structure and Molecular Characterization of Nigerian Field Genebank Collections of Cacao, Theobroma cacao L.

AbstractInadequate knowledge of the population structure and diversity present often hamper the efficient use of germplasm collections. Using a high through-put system, twelve microsatellite loci were used to analyze genetic diversity and population structure in a national field genebank repository of 243 cacao accessions grouped into 11 populations based on their known sources. Based on multi-locus profiles, the Bayesian method was used for individual assignment to verify membership in each population, determine mislabeling and ancestry of some important accessions used in breeding program. A total of 218 alleles was revealed with a mean number of 18.2 alleles per locus. Gene diversity (He= 0.70) and allelic richness (4.34 alleles per locus) were highest in the F1 hybrid population. Differential mating system was suggested as responsible for the observed deficit and excess of heterozygotes observed among the populations. Analysis of molecular variance showed that within-population variance accounted for 63.0% of the total variance while the rest 37% was accounted for by the among-population variance. Cluster dendrogram based on UPGMA revealed two main subsets. The first group was made up of the Amelonado/Trinitario ancestry and the other of Nanay/Parinari ancestry. We found that Nanay and Parinari populations were the major source of Upper Amazon genes utilized while a large proportion of genetic diversity in the field genebank remained under-utilized in development of improved cultivars released to farmers in Nigeria. This study showed that the presence of alleles of the Upper Amazon Forasteros (Nanay, Parinari and Iquitos Mixed Calabacillo) genetic materials in the locally available accessions predated the formal large scale introduction of Upper Amazon materials in 1944. This is the first report of population structure of field genebank collections of cacao in Nigeria since more than seven decades of formal cacao breeding research

Assessment of genetic diversity in horticultural and morphological traits among papaya (

Introduction. Although Nigeria has the largest area planted to papaya (Carica papaya) in the world, this country has one of the lowest yields reported. A good knowledge of the available genetic variability is a first step in the exploitation of this crop for the development of improved cultivars. Until now, there has been no report on genetic diversity in the papaya accessions available in Nigeria. Materials and methods. Sixty accessions of papaya obtained from ten districts in Southeastern Nigeria were evaluated using 21 variables following the IBPGR descriptors for papaya. The data was subjected to descriptive statistics, analysis of variance (ANOVA), and multivariate analysis including principal component (PCA) and cluster analysis. Results. ANOVA showed significant variation among accessions in fruit length, fruit diameter, fruit edible volume, leaf petiole length, fruit shape, flesh color and central cavity shape. The first seven principal component axes accounted for 73.47% of total variation and five cluster groups were generated from cluster analysis. Accessions were classified into two broad groups corresponding to female (15%) and hermaphrodite (85%) plants. A strong and highly significant correlation was found between leaf blade and petiole length and fruit characteristics such as length, diameter and fruit edible volume, a variable derived for the first time in this study. There was a preponderance of yellow flesh color in fruits from female plants and reddish-orange flesh color among hermaphrodite plants. Discussion and conclusions. Each of the five cluster groups consists of accessions that could be used as parents in further breeding or clones for vegetative propagation. This study revealed significant variation that could be exploited for genetic improvement of papaya in Nigeria. It is recommended that a focused papaya genetic improvement program should be pursued to exploit the genetic variation available

Genetic diversity assessment of sub-samples of cacao, Theobroma cacao L., collections in West Africa using simple sequence repeat markers

Knowledge of genebank and on-farm genetic diversity, particularly in an introduced crop species, is crucial to the management and utilization of the genetic resources available. Microsatellite markers were used to determine genetic diversity in 574 accessions of cacao, Theobroma cacao L., representing eight groups covering parental populations in West Africa, genebank, and farmers' populations in Nigeria. From the 12 microsatellite markers used, a total of 144 alleles were detected with a mean allelic richness of 4.39 alleles/locus. The largest genetic diversity was found in the Upper Amazon parent population (H (nb) = 0.730), followed by the 1944 Posnette's Introduction (H (nb) = 0.704), and was lowest in the Local parent population (H (nb) = 0.471). Gene diversity was appreciably high in the farmers' populations (H (nb) = 0.563-0.624); however, the effective number of alleles was lower than that found in the genebank's Posnette's population. Fixation index estimates indicated deficiency of heterozygotes in the Upper Amazon and the Local parent populations (F (is) = 0.209 and 0.160, respectively), and excess of heterozygotes in the Trinitario parent population (F (is) = -0.341). The presence of inbreeding in the Local parent populations and substructure (Wahlund effect) in the Upper Amazon were suggested for the deficiency of heterozygotes observed. Non-significant genetic differentiation observed between the genebank's and farmers' populations indicated significant impact of national breeding programs on varieties grown in farmers' plantations. From this study, we showed that appreciable genetic diversity was present in on-farm and field genebank collections of cacao that can be exploited for crop improvement in West Africa. Suggestions for future conservation of on-farm genetic diversity and local landraces are further discussed