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

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

Tree-to-tree variation in fruits of three populations of Trichoscypha acuminata (Engl.) in Cameroon

Within tree species, phenotypic variation is common and this can affect a species’ domestication. This study was therefore conducted to assess the phenotypic variation in Trichoscypha acuminata fruits in three populations (Nkenglikok, Ndengue and Nkoemvone) in the humid forest zone of Cameroon in view of understanding its selection potential for domestication. A total of 1080 fruits were collected for assessment from 45 trees. The measured traits were fruit diameter (FD), pulp thickness (PT), fruit mass (FM), seed mass (SM), pulp + shell mass (PM+Shell) and germination percentage. Data were analyzed using an ANOVA. Means were separated using Least Significant Difference (LSD) (p = 5%). The results showed that significant (p < 0.05) variation was recorded in FM, PM + Shell, PT, FD, SM, and germination percentage between populations and trees. Nkenglikok seeds scored the best phenotypes including germination compared to the Nkoemvone and Ndengue seeds. The five trees with superior traits for selection (based on PM+Shell, the must usable part) were numbers TA/NK/6, TA/NK/14, TA/NK/12, TA/NK/10 and TA/NK/18. There were correlations between fruit traits on the one hand; and seed germination percentage and FD, SM, and PT on the other. We can conclude that there is phenotypic variation between trees of T. acuminata in terms of FM, FD, PM+Shell, SM, and germination percentage. The study's results can guide for future selection of targeted T. acuminata trees for domestication purposes

Key descriptors for Dacryodes edulis (Safou)

This Descriptor list consists of an initial minimum set of characterization and evaluation descriptors for Dacryodes edulis (Safou). This strategic set aims at facilitating access to and utilization of this African indigenous fruit tree. It does not exclude the addition of other descriptors at a later date. The list was based on a preliminary List developed by World Agroforestry (ICRAF). The strategic set of data standards is designed to facilitate access to and utilization of plant genetic resources for food and agriculture information. Together with passport information (Alercia et al. 2018, 2015), descriptors are critical to the effective sharing of characterization and evaluation data and to the efficient use of plant genetic resources for food and agriculture

Ethnicity Differences in Uses and Management Practices of Bitter Kola Trees (Garcinia kola) in Cameroon

Bitter kola (Garcinia kola) is an indigenous multipurpose tree species in West and Central Africa, threatened by overexploitation and classified by the IUCN as vulnerable. Understanding local knowledge and management patterns in different socioecological contexts could contribute to designing strategies for conservation and long-term use of the species. In order to characterize the parts of the plant and the harvesting techniques that are used by different ethnic groups in Cameroon, we conducted surveys through the use of semi-structured questionnaires (N = 182) in six different sites covering different agro-ecological zones where the species is present (forest and savanna). Ethnic groups from the savanna agro-ecological zone shared similar patterns in G. kola organs/parts used and harvesting techniques, but these patterns differed among ethnic groups from the savanna and forest zones and within the forest zone. Ethnic groups from the savanna zone mainly harvest the species for its seeds that are used as stimulants. Conversely ethnic groups from the forest zone mainly collect bark and roots, and uses differ between agriculturalists (Fang and Bassa) and hunter-gatherers (Baka). These patterns have direct consequences on species management practices. Savanna farmers applied sustainable harvesting as they extract fruits and seeds and planting more trees in order to increase the species’ contribution to their livelihood. People in the forest zone destructively felled standing trees, threatening the species in its natural environment. The influence of these results on the conservation status of the species in the region are discussed

Amenability of priority indigenous fruit trees of West and Central Africa to grafting

Grafting scions of trees with desirable features is an important step for the domestication of indigenous forest fruit trees. Two experiments were carried out in the World Agroforestry (ICRAF) experimental nursery at Yaoundé (Cameroon) to assess the graft success of five forest fruit tree species identified as priority species for domestication in West and Central Africa namely Irvingia gabonensis, Garcinia kola, Cola nitida, Ricinodendron heudelotii and Monodora myristica. In experiment 1, various grafting methods (i.e. side tongue, top cleft, side veneer, and whip-and-tongue) were tested. In experiment 2, three Irvingia species rootstocks (i.e. I. grandifolia, I. gabonensis and I. wombolu) were tested for the grafting of scions of I. gabonensis. Experiment 1 shows that the grafting method significantly affected the percentage of graft success all the tested species except G. kola where all methods resulted in a very high percentage of graft success. The top cleft grafting method had the highest percentage of success, whatever the species. Experiment 2 shows that the type of rootstock significantly influenced the graft success of I. gabonensis scions, with I. wombolu rootstocks showing the highest percentage of graft success at 45.5 ± 7.75%. Our results can guide future propagation programs for these priority fruit tree species for domestication purposes

Effects of pre-severance irradiance on the growth of Allanblackia floribunda Oliv. stockplants and on the subsequent rooting capacity of leafy stem cuttings

The rooting of Allanblackia stem cuttings is typically slow and with the formation of very few roots. Irradiance has positive effects on the relative growth of plants and rooting ability, but there is no information relating to Allanblackia species. Stumps of Allanblackia floribunda Oliv. were grown under three levels of irradiance (2008 mu molm(-2)s(-1), 542 mu molm(-2)s(-1) and 160 mu molm(-2)s(-1)) and were assessed for growth (plant height and the number of cuttings) and the influence of irradiance on the rooting ability of leafy stem cuttings. Shade light regime 542 mu molm(-2)s(-1) resulted in significantly greater stockplant height than in 160 and 2008 mu molm(-2)s(-1). Significantly more useable cuttings were harvested from the tall plants under an irradiance of 542 mu molm(-2)s(-1), fewer from 160 mu molm(-2)s(-1), and the least from 2008 mu molm(-2)s(-1). The rooting ability of cuttings was greatest from stockplants receiving 542 mu molm(-2)s(-1) (>60%) and least from those receiving 160 mu molm(-2)s(-1) (20%). 45% of cutting rooted from stockplants under full sun (2008 mu molm(-2)s(-1)). The speed of rooting of cuttings followed the same ranking with the fastest rooting from plants receiving 542 mu molm(-2)s(-1) (7.1 +/- 1.04weeks to reach 25% of rooting) and the slowest from those under 160 mu molm(-2)s(-1) (12.3 +/- 1.85weeks to reach 25% of rooting). The results of this study demonstrate that the light management of A. floribunda stockplants is important for the maximization of the yielding of cutting and the speed of rooting of leafy stem cuttings. Tree plantation being a key option to alleviate environmental challenges that the world is facing today, these results confirm previous findings which postulates that appropriate light management in stockplants can increase the production speed of required seedlings