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Penja pepper (Piper nigrum) produced in Cameroon has long been recognized for its exceptional organoleptic quality. The pepper vine is grown using a support tree (Spondias mombin) in Cameroon. A root disease is associated with plant deaths in both plants. The disease symptoms are characterized by collar cracking and gummosis and the disease was tentatively identified as Armillaria root rot. In this work the extent of the problem was characterized by surveying 35 farms in Cameroon. Samples were taken from diseased support trees and pepper vines. Support trees exhibiting typical symptoms were found in approximately one third of the surveyed farms. In these farms, disease incidence and Pepper vine mortality ranged from 1.3 to 50% and 1.2 to 87.7%, respectively. Analysis of the ribosomal internal transcribed spacer region (ITS) locus suggested that the isolates collected from S. mombin and P. nigrum are most likely, which is a first for both hosts, represented by Armillaria camerunensis (Henn.) Volk & Burdsall, a fungus previously associated with declining cacao trees in Cameroon. Given the increasing demand for Penja pepper and the great damaging potential of this root rot, research on management strategies should be prioritized.

Studying spatial and temporal plant disease dynamics helps us to understand pathogen dispersal processes and improve disease control recommendations. In this study, three cacao plots devoid of primary inoculum of Phytophthora megakarya (causal agent of cacao black pod rot disease) upon establishment in 2006 were monitored for presence of disease on a weekly basis from 2009 to 2016. Ripley’s K(r) function, join count statistics, and Fisher’s Exact test were used to analyze spatial and temporal disease dynamics. Disease distribution maps showed aggregated disease patterns in all plots; however, for the years of disease onset, exogenous primary infections were mostly randomly distributed. The K(r) function confirmed these results indicating that inoculum generally disperses only over short distances. Moreover, significant positive spatial autocorrelations showed that diseased trees were often clustered up to a distance of 3 to 9 m. Temporal disease progression was low, meaning that endogenous inoculum failed to establish itself, which is partly explained by rigorous phytosanitation and partly by unfavorable microclimatic conditions for disease development. Because P. megakarya had difficulty establishing itself in the plots, proximity to already infected cacao plantations drove infection dynamics. Thus, isolation of newly established cacao plantations from infected ones and rigorous phytosanitation as a preventive strategy appears to be an effective approach to control cacao black pod rot disease for newly established cacao plantations.

Studying spatial and temporal plant disease dynamics helps us to understand pathogen dispersal processes and improve disease control recommendations. In this study, three cacao plots devoid of primary inoculum of

Black pod rot, caused by Phytophthora megakarya, is the main cause of cocoa losses in Cameroon. A few studies have focused on describing black pod epidemics in cocoa yet numerous questions remain. Here, an epidemiological model describing the temporal evolution of cocoa black pod, taking into account the development stages of pods, is developed and studied. In particular, the relative importance of primary and secondary infection in disease dynamics is investigated. Our theoretical study shows the existence of a disease free equilibrium and at least one endemic equilibrium. We highlight two threshold parameters, related to direct and indirect infections that summarize all possible dynamics of the system. Then, based on the literature, we define a periodic pod recruitment function and provide several numerical simulations to study the impact of phytosanitary pod removal on disease dynamics. We show that intense and regular sanitary harvest could lead to complete disease eradication. Our results also highlight the importance of the environmental spores reservoir in disease dynamics, such that future field experiments and observations should focus on it.

Many Phytophthora species have a soil borne phase in their natural life cycles even though disease expression often occurs on aerial plant parts. In Cameroon, black pod rot of cacao (Theobroma cacao L.), is caused by P. megakarya. Primary inoculum of P. megakarya is located in the soil and with the onset of the rainy season, through rain splash, cacao pods become infected. From there the repeated cycles of pod infection and sporulation are at the origin of losses that can reach up to 80% when no control measures are in place. Thus, if this soil borne inoculum could be eliminated or prevented from reaching cacao pods, losses from black pod could be reduced considerably. In Cameroon, successful biological control of black pod rot has been obtained with the use of Trichoderma asperellum PR11 applications directed at cacao pods. The objective of this project therefore, was to investigate the possibility of using T. asperellum PR11 in soil applications in order to reduce primary inoculum and/or reduce black pod disease incidence due to P. megakarya. The study was undertaken in a farmer's field near Nkolbisson, Centre region of Cameroon. Trichoderma asperellum PR11 was applied on a monthly basis over two consecutive production seasons. A water only and a fungicide, Ridomil Gold 66 WP (6 % metalaxyl-M & 60 % CuO) treatment were used as controls. Weekly data collection consisted of counting all healthy and diseased pods. Soil samples were taken at the onset and end of the experiment to determine primary inoculum levels in the soil. For each treatment, six replicate plots each containing 16 cocoa trees were used. The absolute number of rotten pods and percentage pod rot was lower for T. asperellum treated plots when compared with the water control yet higher than the fungicide control, albeit these differences were not significant. There was however, a significant difference between treatments with regard to disease progression over time. Moreover, T. asperellum treatments were very efficient in reducing the amount of primary inoculum in the soil, even more so than the fungicide treatment. Given that T. asperellum applications directed at cacao pods have shown efficiency in controlling black pod rot, the use of soil applications of T. asperellum, which slows disease progression and reduces soil inoculum, should therefore lead to additive effects when both control strategies are employed simultaneously.

BACKGROUND: Field trapping experiments were conducted to evaluate the attractiveness of five different pheromone blends as well as the impact of trap design on attractiveness towards cocoa mirids, Sahlbergella singularis Hagl. and Distantiella theobroma (Dist.), in Cameroon. RESULTS: A total of 361 adults of S. singularis (359 males and two females) were caught. The highest numbers of mirids were found in traps with pheromone blends that combined a monoester and a diester, compared with traps with the diester or the monoester individually and control traps with no pheromone. Rectangular traps caught significantly more mirids compared with delta traps. The mean number of 5.1 mirids trap −1 year −1 caught in rectangular traps was significantly higher compared with the 1.8 mirids trap −1 year −1 for the delta traps. CONCLUSION: The data revealed that rectangular traps containing pheromone blends combining both the monoester and the diester have a good potential to lure and trap adult males of S. singularis on cocoa farms. The pheromone blends used were specific for S. singularis, and the use of pheromone traps appears to be a promising strategy for incorporation into integrated pest management strategies for the monitoring or even the control of S.singularis in cocoa plantations. c � 2011 Society of Chemical Industry

International audience; Shade management is commonly considered to be an effective pest management strategy for cocoa mirids, yet shade management recommendations are not based on extensive knowledge of the mirid ecology in traditional cocoa agroforests.The main objectives of the present study were an assessment of the impact of shade on the spatial distribution of mirid populations and thus the evaluation of shade management strategies.Mirid densities were measured and shade was characterized for three plots located in three different agroecological zones in the Centre region of Cameroon. Mirid densities generally followed a negative binomial law. Geostatistical procedures were used to characterize spatial distribution of mirid density. Light conditions were assessed using hemispherical photography. Populations of Sahlbergella singularis were highly aggregated in the plots.Semivariance analysis and kriging visualized the spatial dependence of miriddensities. Clearly distinguishable mirid pockets of 20–30 adjacent infested cocoa trees were identified in two of the three plots.The high diversity of shade tree species and the large variability in densityand size of shade trees resulted in a considerable heterogeneity of plot lightconditions. Percentage transmitted light varied in the range 9.4–80.1% in the most heterogeneous plot. For two of the three plots, mirid pockets were aggregated in those areas where light transmission was highest. In the third plot, relatively high mirid densities and the presence of an alternative host resulted in a more homogeneous distribution. The importance of these findings for improved mirid control is discussed.

National audience

“Penja Pepper” (Piper nigrum L.) is cultivated in the Penja region of Cameroon. It is famous for its exceptional aroma and taste. However, in Cameroon pepper is attacked by various diseases. Moreover, the support tree used for growing pepper vines in Cameroon, Spondias mombin, is also subject to disease attacks. objectives In order to maintain the viability of Penja Pepper cultivation, these diseases must be identified and controlled. The aim of this study was to identify the principal pathogens of black pepper vines and its support tree. Methods : Samples from pepper vines, S. mombin and the soil were collected from various fields in the Penja region. Using a combination of baiting and selective agar medium techniques several potential causal agents were isolated. The isolated microorganisms were identified based on morphology as well as ITS sequencing. Conclusions : Eight oomycete isolates were obtained from pepper and 18 basidiomycete isolates from either pepper or S. mombin. The eight oomycete isolates of Pepper were tentatively identified as Phytopythium vexans and/or P. cucurbitacearum. The morphological identification of the basidiomycete isolates show that it is an Armillaria sp. Pathogenicity tests were carried out with 180 days old pepper plants. The plants were inoculated with discs of mycelium introduced in the soil and on the collar. This is the first time that Armillaria is found to be pathogenic to pepper as well as its support tree Spondias mombin. The importance of these finding for controlling these diseases to safeguard the sustainable production of the Penja Pepper of Cameroon is discussed.

Les plantains font partie des produits vivriers qui assurent la sécurité alimentaire au Cameroun. Cependant, les rendements de production demeurent faibles à cause de nombreuses contraintes parasitaires, dues notamment à Radopholus similis, nématode qui peut causer jusqu'à 75 % de pertes dans les plantations si aucune mesure de protection n'est entreprise. Dans la plupart des cas, le degré de sensibilité des cultivars locaux de bananier plantain vis-à-vis de R. similis reste inconnu ; ce qui entraîne généralement des rendements très bas, malgré les techniques de lutte employées. Cela constitue un risque à leur vulgarisation à l'échelle nationale. La stratégie de lutte communément utilisée repose essentiellement sur les produits chimiques dont l'usage est polluant, onéreux et contraignant. Dans la recherche des alternatives à la lutte chimique, ce travail a été entrepris pour évaluer la sensibilité de cultivars Essong et Big Ebanga à R. similis et l'effet des formulations de graines de neem (FGN) dans la protection des bananeraies au Cameroun. A cet effet, le pouvoir pathogène de R. similis sur les cultivars Essong et Big Ebanga a été évalué in vivo. Quatre types de FGN [extrait organique, extrait aqueux, huile de neem et poudre de graine de neem] ont été préparées et utilisées pour évaluer leurs effets contre R. similis en champ. Les résultats obtenus montrent que les cultivars Essong et Big Ebanga sont sensibles vis-à-vis de R. similis. L'amendement du sol avec ces formulations a provoqué une réduction de la population de R. similis et une amélioration du rendement en plantain. Ces résultats suggèrent que les graines de neem pourraient être une matière première pour l'application de nouvelles biotechnologies, telle que la formulation de nématicides d'origine naturelle, pourvoyant ainsi une alternative durable à la lutte chimique contre les nématodes du bananier, dans les systèmes de protection intégrée.

Combining crop plants with other plant species in agro-ecosystems is one way to enhance ecological pest and disease regulation mechanisms. Resource availability and microclimatic variation mechanisms affect processes related to pest and pathogen life cycles. These mechanisms are supported both by empirical research and by epidemiological models, yet their relative importance in a real complex agro-ecosystem is still not known. Our aim was thus to assess the independent effects and the relative importance of different variables related to resource availability and microclimatic variation that explain pest and disease occurrence at the plot scale in real complex agro-ecosystems. The study was conducted in cacao (Theobroma cacao) agroforests in Cameroon, where cocoa production is mainly impacted by the mirid bug, Sahlbergella singularis, and black pod disease, caused by Phytophthora megakarya. Vegetation composition and spatial structure, resource availability and pest and disease occurrence were characterized in 20 real agroforest plots. Hierarchical partitioning was used to identify the causal variables that explain mirid density and black pod prevalence. The results of this study show that cacao agroforests can be differentiated on the basis of vegetation composition and spatial structure. This original approach revealed that mirid density decreased when a minimum number of randomly distributed forest trees were present compared with the aggregated distribution of forest trees, or when forest tree density was low. Moreover, a decrease in mirid density was also related to decreased availability of sensitive tissue, independently of the effect of forest tree structure. Contrary to expectations, black pod prevalence decreased with increasing cacao tree abundance. By revealing the effects of vegetation composition and spatial structure on mirids and black pod, this study opens new perspectives for the joint agro-ecological management of cacao pests and diseases at the plot scale, through the optimization of the spatial structure and composition of the vegetation.

Theobroma cacao is currently under serious threat due to various diseases, of which Phytophthora pod rot, commonly called 'black pod' is one of the most economically important. Four fungal species of the same genus are primarily responsible for this disease: P. palmivora, P. megakarya, P. capsici and P. citrophthora. Among these, P. palmivora is the most common, being present in most cacao producing countries. P. palmivora can cause yield losses of 20-30% and tree mortality of 10% annually. P. megakarya occurs only in West African countries, but is the most virulent among the four species. In Africa it causes 30-90% annual crop losses and thus it poses a severe threat to the cacao industry and to producers in Africa. Both in vitro pod husk inoculation assays and in planta pod inoculation assays verified that P. megakarya was more aggressive. Studies suggest effective early penetration by P. megakarya makes it a more destructive pathogen. Since the Phytophthora species that cause disease on cacao differ so much in their virulence, we developed specific primers for QPCR identification of each species. At the same time we characterized the genetic diversity of P. palmivora and P. megakarya in Ghana, a major producer. Through further genetic analysis, we estimate the genome size of P. megakarya to be 116.9 Mb and the P. palmivora genome size to be 100 Mb. P. palmivora appears to be tetraploid whereas P. megakarya, despite its larger genome, is not. Comparative genome analysis between these two species shows that both species carry large numbers of plant-pathogen interaction proteins including the RxLR effectors. An in-depth comparative analysis of genomics and transcriptomics between these two closely related species is being carried out to highlight the molecular mechanism behind their virulence and support the development of effective control measures. This is critical since Phytophthora spp. in general and P. megakarya specifically, represent a significant threat to cacao production and the chocolate industry worldwide. (Texte intégral)