Consecutive retrieval with redundancy: an optimal linear and an optimal cyclic arrangement and their storage space requirements

Information retrieval, file organization, consecutive retrieval property, consecutive retrieval with redundancy, storage space requirements 1

Aspects of average response computation by aperiodic stimulation

A mathematical analysis of the variance of the average evoked-response computation as a function of the numberN of stimuli presented is made for the case when the response is disturbed by additive stationary noise. A comparison is made between the variance for purely periodic stimuli and that for stimuli of which the interstimulus durations are Gaussian distributed. In the latter situation, the interval durations may be correlated with each other, e.g. according to a Gaussian Markov process. It is deduced that, in general, the introduction of aperiodic stimulation tends to make the functional relationship between the variance andN behave as though it holds for noise with a very broad frequency spectrum; the variance is proportional to 1/N

Sterilization of heparinized Cuprophan hemodialysis membranes

The effects of sterilization of dry heparinized Cuprophan hemodialysis membranes by means of ethylene oxide (EtO) exposure, gamma irradiation, or steam on the anticoagulant activity and chemical characteristics of immobilized heparin and the permeability of the membrane were investigated. Sterilization did not result in a release of heparin or heparin fragments from heparinized Cuprophan. Sterilization of heparinized Cuprophan by means of EtO exposure and gamma irradiation induced a slight, insignificant decrease of the anticoagulant activity. In contrast, steam-sterilized heparinized Cuprophan showed a higher anticoagulant activity than unsterilized heparinized Cuprophan, which was most likely caused by cleavage of some of the covalent bonds between heparin and Cupropha. The effects of sterilization on the permeability of unmodified Cuprophan and heparinized Cuprophan were compared. The permeability of unmodified Cuprophan for vitamin B12 (Vit B12) and sulfobromophthalein (SBP) was reduced by 20–35% after EtO exposure and gamma irradiation and was reduced by 90–95% after steam sterilization. The water permeability of unmodified Cuprophan remained the same after EtO exposure and gamma irradiation but also dramatically reduced after steam sterilization. These reductions were ascribed to the collapse of pores of the membrane. The permeability of heparinized Cuprophan was not affected by EtO exposure and gamma irradiation but dramatically reduced after steam sterilization, although to a lesser extent than in the case of unmodified Cuprophan. Apparently, the presence of immobilized heparin (partially) prevented the collapse of pores during sterilization. Gamma irradiation was recommended as the preferred method of sterilization for heparinized Cuprophan.\u

Le taux de wilt est-il un facteur limitant de la production des cacaoyers ?

La production des cacaoyers dépend de nombreux facteurs: le nombre de fleurs produites par arbre, la pollinisation des fleurs, la tenue des jeunes fruits, les dégâts occasionnés par les maladies et les ravageurs. Parmi ces facteurs, nous nous sommes intéressés à la tenue des jeunes fruits, et donc aux pertes dues au cherelle wilt. Le wilt affecte tous les cacaoyers en production et nous avons voulu répondre à la question : le taux de wilt est il un facteur de régulation de la production des arbres, c'est-à-dire, le taux de wilt augmente t'il avec la charge en fruits des arbres ? ou bien, ce taux est il indépendant de la production ? Pour répondre à ces questions, nous avons suivi le chérelle wilt durant 2 années consécutives sur une parcelle de cacaoyers hybrides : les chérelles wiltées, les cabosses malades et les cabosses mures saines ont été répertoriées chaque semaine et sur chaque arbre. Il apparaît que le wilt affecte l'ensemble des arbres même ceux ayant des niveaux de production très faibles et la moyenne du taux de wilt est supérieur à 50 %. Le taux de wilt est relativement constant en fonction de la charge en fruits des arbres jusqu'à une charge totale en fruits d'environ 100 cabosses adultes par arbre. Le wilt intervient donc comme facteur de régulation au delà d'une production par arbre dépassant les 100 cabosses adultes par arbre, soit une production d'environ 4 tonnes de cacao marchand à l'hectare, rendement très rarement atteint en parcelle de production. Le taux wilt est apparu très héritable dans un essai comparatif de clones au Cameroun et il est donc possible de réduire les pertes dues à ce problème par amélioration génétique. Il parait toutefois important d'étudier plus finement les processus physiologiques intervenant dans le wilt pour tenter de diminuer ce phénomène qui touche plus de 50% des jeunes fruits. (Résumé d'auteur

Preventing the spread and mitigating the impact of cocoa diseases in the Caribbean

With the arrival of frosty pod rot (FPR, caused by Moniliophthora roreri) in Jamaica, the insular Caribbean is now home to three of the “big five” of cocoa (Theobroma cacao) diseases. Black pod disease of cocoa (caused by Phytophthora spp.) is ubiquitous in the region whereas witches' broom (WB, caused by M. perniciosa) and FPR are still restricted to a few countries. The recent arrival of FPR however, is particularly worrying since it is considered to be the most destructive of all cocoa diseases. Even though the Caribbean contributes little to global cocoa production, it ranks second when it comes to fine flavor cocoa. Moreover, cocoa remains an important source of revenue for a large number of people in the Caribbean. Unfortunately, much of the varieties grown, known for their fine flavor qualities, have little resistance to diseases, especially FPR and/or WB. On top of that, most cocoa producing countries in the region are poorly equipped to prevent the arrival of FPR or WB or eradicate them once they do arrive. Thus, continual spread of these diseases in the Caribbean will have a severe impact on the fine flavor cocoa sector and the livelihoods of those depending on cocoa. In order to prevent further disease spread within the Caribbean, it is necessary to implement a major programme integrating awareness raising, capacity building, and development of early detection and rapid response measures for eradication. Additionally, countries will have to prepare for when these diseases do become established. The introduction of elite, highly productive cocoa germplasm combining resistance to WB and FPR and good quality attributes is urgently needed. Good agricultural practices that enable maximal expression of these attributes should be developed with and communicated to farmers and other relevant stakeholders. Such an undertaking will have the added benefit of revitalizing the sector and increasing productivity. This can only be successfully realized however, through a concerted effort among all cocoa producing countries bordering or in the Caribbean. There is an urgent need to make this financially and politically feasible. Only through such a concerted effort will cocoa remain a driver for the sustainable development of the Caribbean. (Texte intégral

Probando el control biológico en cacao. CIBB-SIMP-CA-003

Tres enfermedades de mazorcas del cacao (Theobroma cacao) ocasionan grandes pérdidas en las Américas: moniliasis, escoba de bruja (EB) y mazorca negra (MN). Los patógenos responsables son los basidiomicetes Moniliophthora roreri y Moniliophthora perniciosa, así como oomicetes del género Phytophthora, respectivamente. Su control es difícil y costoso, con desafíos comunes: (1) La infección concurrente por Phytophthora spp., M. roreri y/o M. perniciosa requiere biocontrol simultáneo de dos a tres patógenos muy diferentes; (2) La infección latente interna de mazorcas por Moniliophthora spp. restringe la ventana de oportunidad para controlarla; (3) Existe una gran diversidad de esos patógenos, con un rango de susceptibilidades hacía sus controladores potenciales; (4) La altura de los árboles de cacao muchas veces no se presta al manejo fitosanitario. Nuestros objetivos son: (1) compartir lecciones aprendidas con el control biológico de esas enfermedades en el Perú y en Costa Rica y (2) presentar metodologías sencillas para desarrollar exitosamente biocontroladores contra esos patógenos del cacao en otros países del continente. Nuestro enfoque es en agentes fungosos (micoparásitos y hongos endofíticos) para la aplicación inundativa y para el control biológico clásico con biocontroladores co-evolucionados. Recomendamos buscar biocontroladores donde es probable que trabajen naturalmente, en nichos similares a los sitios de aplicación prevista Presentamos la técnica de placas precolonizadas como método de cebo para micoparásitos. La selección de candidatos promisorios a partir de la colección inicial debe usar bioensayos (en vivo) para el pretamizado. Debe ser una eliminación estricta de cualquier organismo que no cumple con todos los requisitos consistentemente aunque sea confrontado con un patógeno pre-establecido así como otra microflora natural. Indicamos varias técnicas sencillas de pretamizado, trabajando con distintas cepas del patógeno en el proceso. Con el fin de controlar patógenos diversos (especies y cepas), proponemos el uso de mezclas de biocontroladores. Las mismas además tiene la ventaja que se pueden diseñar en forma que cubren un rango amplio de condiciones agroecológicos. Pruebas preliminares de campo contra Moniliophthora spp. deben ejecutarse durante un periodo mínimo de 4 meses. Los ensayos de campo se llevan a cabo para un mínimo de dos ciclos de producción. La optimización iterativa de tratamientos eficaces implica no replicar tratamientos que fallaron una vez. Eso invariablemente resulta en diseños experimentales no balanceados y datos faltantes. Paquetes estadísticas modernas pueden analizar estos datos; se recomienda consultar un biometrista ya durante la fase de planificación del estudio para aprovechas al máximo herramientas existentes y datos costosos de ensay del campo. (Résumé d'auteur

Frosty Pod Rot Disease: reducing the risk of its introduction to the ICGT

Frosty Pod Rot disease caused by the basidiomycete Moniliophthora roreri is the most devastating disease of cocoa (Theobroma cacao). This disease, which targets only the pods, can reduce yields by over 80% within a few years after pathogen establishment. In recent years FPR has invaded the last hold ‐ outs in Mesoamerica. It breached Mexico and Belize around 2005, El Salvador around 2009 and expanded its range into South America, entering Bolivia in 2012. Most recently FPR made its first incursion into the Caribbean where it was officially reported in Jamaica, in 2016. This invasive plant pathogen poses a serious threat to the cocoa industry in Trinidad and Tobago as well as the wider Caribbean. The full management cascade recommended for invasive plant pathogens is applicable to Trinidad and Tobago: prevention; early detection and rapid response; and impact mitigation using various control approaches. This paper presents the actions the Cocoa Research Centre, the University of the West Indies, to avoid the arrival of the disease and the measures to be put in place by the Ministry of Agriculture, Lands and Fisheries, Trinidad and Tobago to detect and eradicate FPR if it does. It prioritizes actions to be undertaken to cost‐effectively manage this disease if it should become established in Trinidad and Tobago. (Résumé d'auteur

Reconciling food and perennial export crop production in a changing environment

Perennial export crops such as cocoa and coffee contribute indirectly to food security by providing an income that can be used to buy food and/or the supplies for the cultivation of basic food crops. Thus, any crop loss incurred due to the effects of climate change will also impact food security. A first clear warning of the impact of climate change on perennial export crop production was provided by the climate change driven coffee leaf rust disease crisis in Central America. Coffee production decreased by 16% in 2012-13 and a further 10% in 2013-14 as a consequence of the epidemic. In Central America, these production reductions had direct impacts on the livelihoods of approximately 500 000 smallholders and harvesters and the food security situation of these rural communities. It is foreseen that in the not so distant future (2050) climate change and increased land use for food crop production due to population growth, will negatively impact global production of coffee and cocoa by reducing the amount of suitable arable land. On top of that, the current trend towards full sun systems with excessive use of external inputs (agrochemicals, irrigation) increases the vulnerability of the cocoa and coffee sectors to climate change. To reconcile the need for food crops and the demand for export crops such as coffee and cacao under the scenarios of climate change and population growth, innovative production systems have to be developed. Such systems should also contribute to mitigation of and adaptation to climate change and provide other environmental services such as regulation of pests and diseases. Agroforestry systems are one of the production systems that can reply to these manifold demands. Here an overview is provided of means to develop competitive and sustainable agroforestry systems and the evaluation of environmental services provided

Field optimization of pheromone traps for monitoring and controlling cocoa mirids, Sahlbergella singularis

In Cameroon, pheromone traps appear interesting to monitor or even control Sahlbergella singularis populations on cocoa farms. The efficiency of traps baited with pheromones relies on a good knowledge of both visual and olfactory stimuli that attract cocoa mirids and on appropriate trap deployment in cocoa plantations. The aim of this preliminary study is first to compare the attractiveness of traps of different colors and baited with different pheromone blends. To achieve this purpose, we monitored a total of 90 traps of 3 different colors (30 red, 30 yellow and 30 white) and baited with 2 different pheromone blends, deployed in ten 1-ha plots (100 x 100m) PVC tubular traps were monitored from March on a weekly basis. Simultaneously, experiments in flight tunnel were conducted in the laboratory to confirm trends observed in the field. Secondly, to better understand how trap deployment influences mirid capture rate, we tested 3 trap densities in a total of twenty one 1-ha plots (100 x 100m) which received different treatments: 7 plots with a high trap density (16 traps ha-1), 7 plots with a medium trap density (9 traps ha-1) and 7 plots with a low trap density (4 traps ha-1). Traps were monitored on a weekly basis. Also, mirid populations and damage were assessed in each plot twice a year. Seven plantations with no trap were sprayed with insecticide according to spraying recommendations and were also monitored to evaluate the productivity gain or loss between the two control methods. Understanding the factors involved in oriented movements of mirids in the field, will help to formulate relevant recommendations to improve integrated management of S. singularis and potentially to reduce the economical cost of control strategies. (Résumé d'auteur