Genetic diversity in cocoa germplasm of southern Cameroon revealed by simple sequences repeat (SSRS) markers

The range of polymorphism of about 194 cocoa accessions collected in farms in Southern Cameroon during field surveys and 71 Trinitario and Upper Amazon clones available in genebanks on-station wasassessed using 13 SSR markers. The gene diversity, genetic differentiation and genetic similarities were analysed for the different populations. In total, 282 alleles were detected within all the populations studied. The farm accessions were strongly differentiated based on their geographical origin, with accessions coming from the East province clustering together with local Trinitario accessions from the genebank. Accessions from the Centre-South provinces clustered with Amazon and hybrid accessions, suggesting more uptake of seed garden materials in farms in these provinces. The genetic diversity parameters indicate that the farmers’ planting material is not highly diverse, and is genetically close to parental genotypes available in genebanks. However, some promising Upper Amazon clones (T-clones) that have also been used as parents of released hybrid varieties were genetically distant from the accessions. This result suggests that the progenies of these parents have so far been poorly used in the cocoa farms surveyed. The consequences of these findings for cocoa breeding in Cameroon are discusse

Diversity and pathogenicity of the Ceratocystidaceae associated with cacao agroforests in Cameroon

Knowledge of the diversity and ecology of plant pathogenic fungi in cacao agroforests and surrounding natural ecosystems can inform the development of sustainable management strategies for new cacao disease outbreaks. In this study, we investigated the occurrence of fungi related to the Ceratocystisdaceae and their nitidulid beetle vectors in cacao agroforests in Cameroon, under diverse agroecological conditions. The fungi and their vectors were collected from artificially induced stem wounds on cacao and associated shade trees. Collections were also made from abandoned cacao pod husks and other tree wounds within and around plantations. Fungal isolates were identified using DNA sequence-based phylogenies and morphological comparisons, and two representatives of each species were evaluated for pathogenicity on cacao. Five species of Ceratocystidaceae were recovered, including Huntiella chlamydoformis sp. nov., H. pycnanthi sp. nov. and H. moniliformis, as well as Thielaviopsis cerberus and Th. ethacetica. The incidence of these fungi appeared to be influenced by the prevailing agroecological conditions. Nitidulid beetles in the genus Brachypeplus were found to be their most common insect associates on cacao. Both Th. ethacetica and H. pycnanthi produced extensive lesions after inoculation on branches of mature cacao trees, while Th. ethacetica also caused pod rot. Although their impact remains unknown, fungi in the Ceratocystidaceae and their nitidulid beetle vectors are common and likely contribute to the parasitic pressure in Cameroonian cacao agrosystems.NRF-DST Centre of Excellence in Tree Health Biotechnology (CTHB) of South Africa and the Department of Corporate International Relations of the University of Pretoria through a postgraduate ‘study abroad grant’.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-30592017-01-31hb2016Forestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog

Participatory cocoa (Theobroma cacao) selection in Cameroon: Phytophthora pod rot resistant accessions identified in farmers fields

As part of a participatory selection programme, promising individual trees were selected in 2004 in cocoa farms of southern and western Cameroon regions for yield and for low incidence of Phytophthora pod rot (Ppr) caused by Phytophthora megakarya. The aim of this study was to compare the levels of resistance to Ppr between farm accessions (FA), introduced and local genebank accessions (GA). In total, 234 FA were grafted in the nursery together with 22 introduced GA and 73 local GA, and tested for resistance to P. megakarya by leaf disc inoculations. The introduced GA, that were reported as resistant to Ppr in other countries, proved to be more resistant than the selected FA and unselected FA and also more resistant than the 3 control clones for Ppr resistance used in the study. However, approximately 10% of the FA were as resistant as the average of the introduced GA, showing the potential of selection for resistance to Ppr in farmers’ fields. The average level of resistance of the FA was relatively higher than that of the local GA. The FA selected for yield and low Ppr incidence in the field were more resistant in the leaf disc test than the unselected FA. The use of FA and of farmers’ knowledge in the participatory selection process is valuable in obtaining Ppr-resistant cultivars

Diversification des exploitations agricoles à base de cacaoyer au Centre Cameroun : mythe ou réalité ?

Diversification of cocoa farms in the Central Cameroon: myth or reality? A survey was conducted among 1,171 farmers to assess the degree of diversification on cocoa-based farms in the Centre Province of Cameroon, which is the main cocoa producing zone in the country. Fifteen years after the onset of liberalization of the cocoa supply chain, the results showed that area under cocoa predominates in the cropping plan on a farming system scale. The same applied for the contribution made by cocoa income to overall farm functioning. However, a further study carried out on 74 cocoa plantations in that region showed that diversification was more perceptible on the cocoa based production systems. In fact, fruit tree species, which are very often found in cocoa plantations, partly explained the occurrence of substantial agrobiodiversity. A north – south gradient was found in which diversification of the cocoa growing system was significantly greater in the forest – savannah transition zone than in the forest zone. However, it turned out that the process of diversification by planting fruit tree species in cocoa plantations was not a new phenomenon, since it involved all cocoa plantings whatever their age. This research thus relativizes the extent of the diversification strategy adopted by cocoa producers in the Centre Province of Cameroon in response to changes in their socioeconomic environment and the instability of international markets

Genetic diversity in cocoa germplasm of southern Cameroon revealed by simple sequences repeat (SSRS) markers

The range of polymorphism of about 194 cocoa accessions collected in farms in Southern Cameroon during field surveys and 71 Trinitario and Upper Amazon clones available in genebanks on-station was assessed using 13 SSR markers. The gene diversity, genetic differentiation and genetic similarities were analysed for the different populations. In total, 282 alleles were detected within all the populations studied. The farm accessions were strongly differentiated based on their geographical origin, with accessions coming from the East province clustering together with local Trinitario accessions from the genebank. Accessions from the Centre-South provinces clustered with Amazon and hybrid accessions, suggesting more uptake of seed garden materials in farms in these provinces. The genetic diversity parameters indicate that the farmers’ planting material is not highly diverse, and is genetically close to parental genotypes available in genebanks. However, some promising Upper Amazon clones (T-clones) that have also been used as parents of released hybrid varieties were genetically distant from the accessions. This result suggests that the progenies of these parents have so far been poorly used in the cocoa farms surveyed. The consequences of these findings for cocoa breeding in Cameroon are discussed