Impact de la Cochenille Phenacoccus manihoti (Homoptera, Pseudococcidae) sur les rendements du manioc (Manihot esculenta) au Gabon

La cochenille Phenacoccus manihoti est l’une des causes de la chute des rendements du manioc au Gabon. Par la randomisation, nous avons étudié  son impact sur la croissance de la plante et sur les rendements du manioc. P. manihoti réduit la croissance des plants à 40%, la distance entrenoeuds  des tiges à 45%. Il diminue le nombre, la longueur et le diamètre des tubercules ; respectivement pour le nombre de 7 à 4, de 34 à 9  cm pour la longueur et de 10 à 5 cm pour le diamètre en moyenne. L’action de la cochenille P. manihoti induit ainsi la dimunition de la croissance des  plants et la baisse des rendements du manioc au Gabon. Pour protéger le manioc contre la cochenille, nous pensons que l’utilisation des  techniques de lutte efficaces est indispensable. Elles pourraient même être associées, dans le cadre d’une lutte intégrée, excluant complètement la  lutte chimique, à l’origine de beaucoup de problèmes environnementaux. Les auteurs ont enfin attiré l’attention des gouvernements africains sur la  nécessité de promouvoir les politiques de développement agricole dans leurs pays. English title: Impact of the mealybug Phenacoccus manihoti (homoptera, pseudococcidae) on the yields of the cassava (Manihot esculenta) in Gabon The mealybug Phenacoccus manihoti is one of the causes in the drop of cassava yields in Gabon. Through the randomization, we have studied its  impact on the growth of the plant and on the yields of the cassava. P. manihoti reduces the growth of the plants to 40%, the interval among knots of  the stems to 45%. Its diminishes the number, the length and the diameter of the tubercules, respectively for the number of 7 to 4; of 34 to 9cm for  the length and for 10 to 5cm for the average diameter. Thus, the share of the mealybug P. manihoti induces the lessening of the growth of the plants  and the drop of the cassava yields in Gabon. For protect the cassava against the mealybug we think that the using of the efficient fight  techniques is indispensable. They must even be assoociated in integrated fight excuding completely the chemical fight which induces meny  environemental problems. At last the authors have attracted the car of the african governments abut the necessity to upgrade the agricultural  development politics in theirs contries.&nbsp

CASSAVA MOSAIC DISEASE INCIDENCE AND SEVERITY AND WHITEFLY VECTOR DISTRIBUTION IN GABON

Cassava mosaic disease (CMD) is a major constraint to cassava ( Manihot esculenta Crantz) production in sub-Saharan Africa. The objective of this study was to gain insights into the epidemiology of CMD in cassava production systems in Gabon. An epidemiological survey was conducted throughout Gabon from October 2020 to May 2021 to evaluate the epidemiology of cassava mosaic disease (CMD) in cassava farms. A phytosanitary diagnosis was conducted at each farm, using the harmonised and unified WAVE protocol to assess the incidence and severity of CMD and the abundance of its whitefly vector. All data collected were recorded using WAVE\u2019s mobile application and uploaded into the WAVE Cube data system. The results showed that CMD was present in all farms surveyed (n = 227; 100%), but with a variable incidence rate. At national level, the incidence of CMD was high, with an average of 64.29%. However, incidence differed among regions with 82.22 and 79.20% for Ogooue-Maritime and Nyanga; respectively, but only 40.42% for Estuaire. Woleu-Ntem had the highest mean severity (3.47) and Ogooue-Maritime the lowest (2.64). Overall, incidence and severity differed significantly among regions (P< 0.05). The average abundance was 2.58 whiteflies per plant (w/p), varying between 1.06 (Nyanga) and 5.25 w/p (Estuaire). The use of infected cuttings was the main mode of CMD spread (62.67%). These results highlight the need to identify the viruses responsible for the observed cases of CMD, to sanitise cultivated plant material, and to implement a CMD control strategy in Gabon.La maladie de la mosa\uefque du manioc (CMD) est une contrainte majeure \ue0 la production de manioc (Manihot esculenta Crantz) en Afrique subsaharienne. L\u2019objectif de cette \ue9tude \ue9tait de mieux comprendre l\u2019\ue9pid\ue9miologie de la CMD dans les syst\ue8mes de production de manioc au Gabon. Une enqu\ueate \ue9pid\ue9miologique a \ue9t\ue9 men\ue9e dans tout le Gabon d\u2019Octobre 2020 \ue0 Mai 2021 afin de mieux connaitre l\u2019\ue9pid\ue9miologie de la mosa\uefque du manioc. Un diagnostic phytosanitaire a \ue9t\ue9 fait dans chaque champ prospect\ue9. L\u2019incidence, la s\ue9v\ue9rit\ue9 de la mosa\uefque et l\u2019abondance des mouches blanches vectrices ont \ue9t\ue9 estim\ue9es en utilisant le protocole harmonis\ue9 et unifi\ue9 du programme WAVE. Toutes les donn\ue9es de terrain ont \ue9t\ue9 saisies gr\ue2ce \ue0 l\u2019application mobile de WAVE puis stock\ue9es dans le gestionnaire de donn\ue9es de WAVE, le Cube. Les r\ue9sultats de cette \ue9tude ont montr\ue9 que la mosa\uefque du manioc \ue9tait pr\ue9sente dans toutes les zones prospect\ue9es (n = 227; 100%), avec une incidence variable. Au niveau national, l\u2019incidence de la CMD \ue9tait \ue9lev\ue9e, avec une moyenne de 64,29% pour une s\ue9v\ue9rit\ue9 moyenne de 3,16. Cette incidence varie entre les provinces avec respectivement 82,22% et 79,20% pour l\u2019Ogoou\ue9-Maritime et la Nyanga, mais seulement, 40,42% pour l\u2019Estuaire. La r\ue9gion du Woleu-Ntem a pr\ue9sent\ue9 la plus grande s\ue9v\ue9rit\ue9 moyenne (3,47) et l\u2019Ogoou\ue9-Maritime, la plus faible moyenne (2,64). L\u2019incidence et la s\ue9v\ue9rit\ue9 ont diff\ue9r\ue9 significativement entre les r\ue9gions (P< 0,05). L\u2019abondance moyenne des mouches blanches \ue9tait de 2,58 mouches/plante (m/p). Cette abondance a oscill\ue9 entre 1,06 m/p (Nyanga) et 5,25 m/p (Estuaire). L\u2019utilisation des boutures de manioc infect\ue9es est le principal mode de propagation de la CMD (62,67%). Ces r\ue9sultats pr\ue9liminaires mettent en exergue la n\ue9cessit\ue9 imp\ue9rieuse d\u2019identifier les virus responsables des cas de CMD observ\ue9s, d\u2019assainir le mat\ue9riel v\ue9g\ue9tal cultiv\ue9 et de mettre en place une strat\ue9gie de contr\uf4le de la CMD au Gabon

Diagnostic performance and comparison of ultrasensitive and conventional rapid diagnostic test, thick blood smear and quantitative PCR for detection of low-density Plasmodium falciparum infections during a controlled human malaria infection study in Equatorial Guinea

BACKGROUND: Progress towards malaria elimination has stagnated, partly because infections persisting at low parasite densities comprise a large reservoir contributing to ongoing malaria transmission and are difficult to detect. This study compared the performance of an ultrasensitive rapid diagnostic test (uRDT) designed to detect low density infections to a conventional RDT (cRDT), expert microscopy using Giemsa-stained thick blood smears (TBS), and quantitative polymerase chain reaction (qPCR) during a controlled human malaria infection (CHMI) study conducted in malaria exposed adults (NCT03590340). METHODS: Blood samples were collected from healthy Equatoguineans aged 18-35 years beginning on day 8 after CHMI with 3.2 x 10(3) cryopreserved, infectious Plasmodium falciparum sporozoites (PfSPZ Challenge, strain NF54) administered by direct venous inoculation. qPCR (18s ribosomal DNA), uRDT (Alere Malaria Ag P.f.), cRDT [Carestart Malaria Pf/PAN (PfHRP2/pLDH)], and TBS were performed daily until the volunteer became TBS positive and treatment was administered. qPCR was the reference for the presence of Plasmodium falciparum parasites. RESULTS: 279 samples were collected from 24 participants; 123 were positive by qPCR. TBS detected 24/123 (19.5% sensitivity [95% CI 13.1-27.8%]), uRDT 21/123 (17.1% sensitivity [95% CI 11.1-25.1%]), cRDT 10/123 (8.1% sensitivity [95% CI 4.2-14.8%]); all were 100% specific and did not detect any positive samples not detected by qPCR. TBS and uRDT were more sensitive than cRDT (TBS vs. cRDT p = 0.015; uRDT vs. cRDT p = 0.053), detecting parasitaemias as low as 3.7 parasites/microL (p/microL) (TBS and uRDT) compared to 5.6 p/microL (cRDT) based on TBS density measurements. TBS, uRDT and cRDT did not detect any of the 70/123 samples positive by qPCR below 5.86 p/microL, the qPCR density corresponding to 3.7 p/microL by TBS. The median prepatent periods in days (ranges) were 14.5 (10-20), 18.0 (15-28), 18.0 (15-20) and 18.0 (16-24) for qPCR, TBS, uRDT and cRDT, respectively; qPCR detected parasitaemia significantly earlier (3.5 days) than the other tests. CONCLUSIONS: TBS and uRDT had similar sensitivities, both were more sensitive than cRDT, and neither matched qPCR for detecting low density parasitaemia. uRDT could be considered an alternative to TBS in selected applications, such as CHMI or field diagnosis, where qualitative, dichotomous results for malaria infection might be sufficient

The GALAXIES inelastic hard X-ray scattering end-station at Synchrotron SOLEIL

International audienceGALAXIES is an in-vacuum undulator hard X-ray micro-focused beamline dedicated to the study of the electronic structure of materials with high energy resolution using both photoelectron spectroscopy and inelastic X-ray scattering and under both non-resonant (NR-IXS) and resonant (RIXS) conditions. Due to the penetrating power of hard X-rays and the 'photon-in/photon-out' technique, the sample environment is not a limitation. Materials under extreme conditions, for example in diamond anvil cells or catalysis chambers, thus constitute a major research direction. Here, the design and performance of the inelastic X-ray scattering end-station that operates in the energy range from $ 4 keV up to 12 keV is reported, and its capabilities are highlighted using a selection of data taken from recently performed experiments. The ability to scan 'on the fly' the incident and scattered/emitted X-ray energies, and the sample position enables fast data collection and high experimental throughput. A diamond X-ray transmission phase retarder, which can be used to generate circularly polarized light, will also be discussed in the light of the recent RIXS-MCD approach

Tuber formation and development of Dioscorea cayenensis-D. rotundata complex in vitro. Effect of polyamines.

Tuberisation was obtained in vitro on yam (Dioscorea cayenensis-D.rotundata complex). The effect of exogenous polyamines on tuber formation and development (length and weight of microtubers) were investigated and discussed in relation with changes in endogenous polyamines. Application of exogenous polyamines, inhibitors of their metabolism and polyamines precursors in various concentrations positively affected microtuber formation by yam nodal cuttings and their further development. In control conditions, three weeks are needed to obtain 100% of tuberisation. With low concentrations of putrescine (10 5 or 10 6 M), tuber formation occurred earlier. Polyamine endogenous level and metabolism can be significantly affected by exogenous polyamines but modifications of endogenous free polyamines could not be directly correlated to the tuber formation process. Increases in endogenous putrescine and auxins were observed in tubers showing a better development in the presence of putrescine. These results can be used for optimising in vitro conditions for mass production of larger microtubers of the Dioscorea cayenensis-D. rotundata complex