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

Genetic diversity in African nutmeg (Monodora myristica) accessions from South Eastern Nigeria

Twenty-one accessions of African nutmeg (Monodora myristica Gaertn. Dunal), an endangered spice plant, were collected from the South-East and South-South regions of Nigeria and analyzed for genetic diversity using random amplified polymorphic DNA (RAPD) markers. Twenty-one (21) decamer primers were tested out of which 10 that gave reproducible band patterns were selected for the study. A total of 77 bands were generated, ranging from 3 for OPB17 to 13 for OPT07, and were all polymorphic. The mean polymorphic information content (PIC) and genetic diversity (He) were 0.673 and 0.697, respectively, indicating high genetic variation among the accessions. Cluster analysis delineated the accessions into four major groups. The maximum similarity index (0.88) based on Dice coefficient was recorded between AGL-01 and CRS-01 while the least (0.13) was between UGA-02 and EKW 01. The derived data was thus able to determine the extent of molecular variation underlying RAPD size polymorphism. Results obtained from this study proved that RAPD could be successfully used as a molecular tool for diversity study in M. myristica. The distributive pattern of genetic variation of M. myristica accessions provides important baseline data for conservation and improvement strategies for this species.Keywords: African nutmeg, random amplified polymorphic DNA (RAPD), genetic variation, polymorphic information content (PIC), similarity index, Monodora myristicaAfrican Journal of Biotechnology, Vol 13(42) 4105-411

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

Effect of pre-budwood collection treatment on budding success in cocoa (Theobroma cacao L)

The inconsistencies in success of budding exercises pose great problem in the rapid multiplication of desirable genotypes for germplasm, clonal plot and seed garden establishment in cacao, Theobroma cacao L. This study was carried out at Cocoa Research Institute of Nigeria, Ibadan to determine the effects of pre-budwood collection treatments of twig on bud take and sprout. Four treatments (i) whole leaf clip (ii) half leaf clip (iii) apical bud clip and (iv) twig wounding at the point of budwood collection and (v) a control (budwood collection and budding on the same day) were applied. Budwoods were collected 2, 4, 6, 8 and 10 days after treatment (DAT) giving a factorial experiment of 5 x 5 in a randomized complete block design. Clone Na 32 was used for this experiment. Results showed that the wounding treatment gave a significantly greater (p < 0.001) bud take than all other treatments for all the days under study. At 2 – 6 DAT, there was no significant difference (p < 0.609) between the wounding treatment (68% - 82%) and the control (48% - 72%). However, at 8 – 10 DAT, bud take in the wounding treatment (76% - 88%) was significantly higher than the control (40% -56%). Assessment of sprouts and green buddings four weeks after opening showed that the wounding treatment consistently gave a significantly higher percentage (p < 0.001) budding success (46% - 72%) than the control (26% - 54%) for all the days studied. This strongly showed that the wounding treatment even at two days before budwood collection greatly increased bud take and sprouts and hence, budding success than in the conventional method. This study underscores the potential advantage of twig pre-treatment before budwood collection for increased budding success in cacao. Key words: Pre-budwood; budding success; cacao; Theobroma cacao L.; germplasm. Moor Journal of Agricultural Research Vol.4(2) 2003: 206-20

Phosphorus adsorption pattern in selected cocoa growing soils in Nigeria

Application of phosphate fertilizer for the correction of P deficiency in soil is ideal in agricultural practices. Unfortunately, only a small fraction of applied P fertilizer is available for plant uptake due to fertilizer-soil interactions which leads to fixation of P. phosphorus adsorption isotherm and buffering capacity are strong tools for predicting response of different soil types to applied P fertilizers. The study was carried out to investigate the degree of P adsorption capacity in selected cocoa soils in Nigeria. Owena, Ibadan and Ikom soils were equilibrated with solutions of 20, 30, 40, 50, 60, 70 and 80 mg P L-1 prior to evaluating sorption capacity and binding intensity. Result indicated that at any specific P concentration, adsorbed P was higher in Ikom soil than Owena and Ibadan soils. Langmuir equation gave better goodness-of- fit than Freundlich equation. The soil’s ability to sorb added P increases due to increase in clay, aluminium and iron content. Hence, Ikom soil with the highest clay, Al and Fe will require more phosphorus fertilization to attain optimum phosphorus concentration in soil solution compared with Owena and Ibadan soils. However, Ikom soil will serve as the best reservoir of phosphorus due to its high P-buffering capacity.Keywords: Fertilizer, Freundlich, Langmuir, Isotherm, aluminium, cla