Methodological approaches for the selection of genotypes in a progeny trial of Dacryodes edulis (G. Don) H. J. Lam in Cameroon

The World Agroforestry Centre (ICRAF) initiated a program in Cameroon for the selection of improved genotypes of Dacryodes edulis for domestication. There are major challenges in such selection because superior performance of individual trees may be based on site conditions rather than on genetic differences. Open-pollinated seeds were collected from mother trees in four provenances in Cameroon and planted in a progeny trial at Minkoameyos, Cameroon. Progeny from the same mother tree are referred to as family. After one year of growth in the field, growth traits were measured annually for five years and fruit traits were measured in two successive years. Three methodological approaches were investigated: family and within-family selection (combined selection), ranking for phenotypic selection and correlation for multi-trait and early selection. Variation in growth and fruit traits among families was not significant for most provenances, indicating that family selection would not be effective for the selection of genotypes in the trial. Phenotypic selection resulted in the retention of a small number of individuals of all families in the trial. There were strong positive correlations between fruit traits and between fruit and growth traits, while negative correlations were found between fruit traits and yield. The correlations indicate that selecting for one fruit trait may also improve the other fruit traits but reduce fruit yield. Positive and significant juvenile-mature correlations for growth were also found in this trial, indicating that early selection may be possible based ongrowth. Based on these results, phenotypic selection is recommended in the progeny trial for the domestication program in Cameroon and further research on early selection is needed as the trial advances in age

Analysis of genetic diversity in accessions of Irvingia gabonensis (Aubry-Lecomte ex O'Rorke) Baill

Amplified fragment length polymorphism (AFLP) was used to assess genetic diversity and relationships among 15 accessions of Irvingia gabonensis collected from Cameroun, Gabon, and Nigeria. Twelve AFLP+3 primers produced 384 polymorphic fragments. Average genetic distance (AGD) between the 15 accessions was 58.7% (32-88%). AGD and range of genetic distance among accessions from Cameroun, Nigeria and Gabon were 62% (53-76%), 52% (32.3 – 84.8%) and 50% (45- 53%), respectively, indicating more genetic diversity in Cameroun than Nigeria and Gabon. The unweighted pair-group method of the arithmetic average (UPGMA) and principal coordinate analysis (PCO) showed a clear distinction between the Gabon and Nigeria accessions into two separate clusters, with accessions from Cameroun overlapping them. Principal coordinate analysis (PCO) indicated a closer relationship between accessions from Cameroun and Gabon. In general the Cameroun germplasm appears to be a bridge between the genetically isolated Nigeria and Gabon accessions. This overlap of Gabon and Nigerian accessions by the accessions from Cameroun may be an indication that Cameroun is the center of diversity of I. gabonensis and also the primary source of original materials grown in the other countries. More collection in Cameroun is necessary to ensure the optimum collection and preservation of the existing genetic diversity in I. gabonensis.Keywords: Irvingia gabonensis, Accession, amplified fragment length polymorphism, genetic diversit

Influence de la provenance du géniteur et du type de pollen sur la fructification sous pollinisation contrôlée chez Dacryodes edulis (Burseraceae) au Cameroun

Très peu de travaux ont été réalisés sur l’amélioration variétale des espèces locales. L’amélioration de leur germoplasme aboutit à l’obtention du matériel végétal amélioré destiné à la création de nouveaux cultivars. Des essais de pollinisations croisées contrôlées ont été menés sur Dacryodes edulis dans le but d’évaluer l’influence de la provenance des géniteurs et du type de pollen sur la fructification de 14 accessions femelles issues de 03 provenances. Les croisements ont été effectués selon un schéma en bloc imbriqué. Pour chaque croisement effectué, le nombre de fleurs pollinisées, le nombre de fruits noués et le nombre de fruits arrivés à maturité ont été évalués; le taux de nouaison (TN), l’indice de fructification (IF) et le taux de chute des fruits (TC) calculés et soumis à une analyse de variance. A partir des moyennes obtenues, les différentes combinaisons ont été classées en fonction de leur performance à l’aide du ‘cluster analysis’. Les résultats obtenus ont montré que l’indice de fructification qui détermine le rendement de l’espèce étudiée varie uniquement et de manière significative (p=0,010) sous l’action combinée des trois facteurs étudiés. Six meilleures combinaisons caractérisées principalement par un taux de nouaison, un taux de fructification élevés et un faible taux de chute de fruits après nouaison (plus de 70%, plus de 50% et moins de 20% respectivement) ont été identifiées. Les graines des fruits (hybrides F1) issues de cette étude ont été caractérisées et les plants ont été produits en pépinière. Ces derniers serviront de matériel de base d’un essai clonal dans un futur proche.Mots clés: Banque de gènes, essai clonal, germoplasme, safoutier, pollinisation contrôlé

The management of tree genetic resources and the livelihoods of rural communities in the tropics: non-timber forest products, smallholder agroforestry practices and tree commodity crops

Products and services provided by trees in forests and farmland support the needs and promote the wellbeing of hundreds of millions of people in the tropics. Value depends on managing both the diversity of tree species present in landscapes and the genetic variation within these species. The benefits from trees and their genetic resources are, however, often not well quantified because trade is frequently outside formal markets, there is a multiplicity of species and ways in which trees are used and managed, and genetic diversity within species is frequently not given proper consideration. We review here what is known about the value of trees to rural communities through considering three production categories: non-timber products harvested from trees in natural and managed forests and woodlands; the various products and services obtained from a wide range of trees planted and/or retained in smallholders’ agroforestry systems; and the commercial products harvested from cultivated tree commodity crops. Where possible, we focus on the role of intra-specific genetic variation in providing support to livelihoods, and for each of the three production categories we also consider wider conservation and sustainability issues, including the linkages between categories in terms of management. Challenges to ‘conventional wisdom’ on tree resource use, value and management – such as in the posited links between commercialisation, cultivation and conservation – are highlighted, and constraints and opportunities to maintain and enhance value are described

Ensuring the future of the pygeum tree (Prunus africana)

This report is aimed at trainers and support organisations for farmers and tree owners, as well as commercial tree nursery operators, government extension agencies and NGOs, among others, who are interested in cultivating the pygeum tree