Perspective article: Food security in tropical Africa through climate-smart plant health management.

Each year, Africa loses half of its harvest to pests (insects, pathogens, nematodes, weeds). To offset these losses and improve food security, pest management needs to be revamped urgently. Based on a synthesis of all 58 pest management projects conducted by IITA in its 55-year history, we advocate here for the implementation of the five following key climate-smart interventions, which have been shown to increase yields and decreasing CO2 outputs compared to the current practices that are largely based on the use of synthetic pesticides: 1. Sanitation at the country's borders and at the field level is the most cost-efficient way to prevent pest damage and losses from exotic pests entering new territories. 2. Good soil management strengthens the crop plant and enhances the effectiveness of all other interventions. 3. Biological control is the quickest and in the long run most cost-effective way to control invading insect pests and weeds. 4. Resistant varieties are often the only way to control already established diseases and are a mainstay control method in combination with other practices. 5. Various bio-pesticides based on viruses, bacteria and fungi against insects have been commercialized or can be produced on-farm; they are to replace synthetic pesticides, which continue to have large negative impacts on the environment and human health. To apply these five practices, new decision-support and climate services tools should be used to empower low-literacy farmers to take timely decisions about pest control and to act as business partners. Meanwhile, all actors in the pest control community should account for their environmental costs, which up to now are born solely by the community, while profits from pesticide sales are pocketed privately. To successfully disseminate these practices across the continent, enhanced and harmonized policy support is required.

Classical biological of key horticultural pests in Africa: successes, challenges, and opportunities.

Classical biological control (CBC) is considered a safer and more sustainable alternative for management of alien-invasive species. This review presents recent advances in CBC of key horticultural insect pests using parasitoids in Africa. Several CBC programs have been undertaken targeting different insect pests of both fruits and vegetables, largely yielding outstanding success. Key obstacles impeding CBC and opportunities that could promote CBC in Africa are outlined. Also, very brief highlights on recent scientific and technological advances in modeling, integrative taxonomy and molecular tools, and endosymbionts that relate to CBC are provided.

Continental-scale suppression of an invasive pest by a host-specific parasitoid underlines both environmental and economic benefits of arthropod biological control.

Biological control, a globally-important ecosystem service, can provide long-term and broad-scale suppression of invasive pests, weeds and pathogens in natural, urban and agricultural environments. Following (few) historic cases that led to sizeable environmental up-sets, the discipline of arthropod biological control has-over the past decades-evolved and matured. Now, by deliberately taking into account the ecological risks associated with the planned introduction of insect natural enemies, immense environmental and societal benefits can be gained. In this study, we document and analyze a successful case of biological control against the cassava mealybug, Phenacoccus manihoti (Hemiptera: Pseudococcidae) which invaded Southeast Asia in 2008, where it caused substantial crop losses and triggered two- to three-fold surges in agricultural commodity prices. In 2009, the host-specific parasitoid Anagyrus lopezi (Hymenoptera: Encyrtidae) was released in Thailand and subsequently introduced into neighboring Asian countries. Drawing upon continental-scale insect surveys, multi-year population studies and (field-level) experimental assays, we show how A. lopezi attained intermediate to high parasitism rates across diverse agro-ecological contexts. Driving mealybug populations below non-damaging levels over a broad geographical area, A. lopezi allowed yield recoveries up to 10.0 t/ha and provided biological control services worth several hundred dollars per ha (at local farm-gate prices) in Asia's four-million ha cassava crop. Our work provides lessons to invasion science and crop protection worldwide. Furthermore, it accentuates the importance of scientifically-guided biological control for insect pest management, and highlights its potentially large socio-economic benefits to agricultural sustainability in the face of a debilitating invasive pest. In times of unrelenting insect invasions, surging pesticide use and accelerating biodiversity loss across the globe, this study demonstrates how biological control-as a pure public good endeavor-constitutes a powerful, cost-effective and environmentally-responsible solution for invasive species mitigation.

Synthesis, characterization and histomorphometric analysis of cellular response to a new elastic DegraPol® polymer for rabbit Achilles tendon rupture repair.

Tendon rupture repair is a surgical field where improvements are still required due to problems such as repeat ruptures, adhesion formation and joint stiffness. In the current study, a reversibly expandable and contractible electrospun tube based on a biocompatible and biodegradable polymer was implanted around a transected and conventionally sutured rabbit Achilles tendon. The material used was DegraPol® (DP), a polyester urethane. To make DP softer, more elastic and surgeon-friendly, the synthesis protocol was slightly modified. Material properties of conventional and new DP film electrospun meshes are presented. At 12 weeks post-surgery, tenocyte and tenoblast density, nuclei and width, collagen fibre structure and inflammation levels were analyzed histomorphometrically. Additionally, a comprehensive histological scoring system by Stoll et al. (2011) was used to compare healing outcomes. Results showed that there were no adverse reactions of the tendon tissue following the implant. No differences were found whether the DP tube was applied or not for both traditional and new DP materials. As a result, the new DP material was shown to be an excellent carrier for delivery of growth factors, stem cells and other agents responsible for tendon healing.

Cellular response of healing tissue to DegraPol tube implantation in rabbit Achilles tendon rupture repair: an in vivo histomorphometric study.

In tendon rupture repair, improvements such as higher primary repair strength, anti-adhesion and accelerated healing are needed. We developed a potential carrier system of an electrospun DegraPol tube, which was tightly implanted around a transected and conventionally sutured rabbit Achilles tendon. Histomorphometric analysis of the tendon tissue 12 weeks postoperation showed that the tenocyte density, tenocyte morphology and number of inflammation zones were statistically equivalent, whether or not DegraPol tube was implanted; only the collagen fibres were slightly less parallelly orientated in the tube-treated case. Comparison of rabbits that were operated on both hind legs with ones that were operated on only one hind leg showed that there were significantly more inflammation zones in the two-leg cases compared to the one-leg cases, while the implantation of a DegraPol tube had no such adverse effects. These findings are a prerequisite for using DegraPol tube as a carrier system for growth factors, cytokines or stem cells in order to accelerate the healing process of tendon tissue.

Three-dimensional co-cultures of osteoblasts and endothelial cells in DegraPol foam: histological and high-field magnetic resonance imaging analyses of pre-engineered capillary networks in bone grafts.

Tissue engineering of bone grafts was addressed in a critical-sized model on the chick chorioallantoic membrane model, using DegraPol(®) foam as scaffold material. The scaffolds were seeded with cultures of human osteoblasts and human endothelial cells, respectively, or with a co-culture of the two cell types (control: no cells). In vitro samples (7 days cultivation) and ex vivo chorioallantoic membrane model samples at incubation day 15 were analyzed by high-field magnetic resonance imaging (MRI) and histology. The co-culture system performed best with respect to perfusion, as assessed by contrast-enhanced MRI using gadolinium-diethylene-triamine-pentaacetic acid (DTPA). The scaffold seeded by the co-culture supported an increased vascular ingrowth, which was confirmed by histological analysis. DegraPol foam is a suitable scaffold for bone tissue engineering and the MRI technique allows for nondestructive and quantitative assessment of perfusion capability during early stages of bone forming constructs.

Cyclic mechanical stimulation favors myosin heavy chain accumulation in engineered skeletal muscle constructs.

PURPOSE: Since stretching plays a key role in skeletal muscle tissue development in vivo, by making use of an innovative bioreactor and a biodegradable microfibrous scaffold (DegraPol(R)) previously developed by our group, we aimed to investigate the effect of mechanical conditioning on the development of skeletal muscle engineered constructs, obtained by seeding and culturing murine skeletal muscle cells on electrospun membranes. METHODS: Following 5 days of static culture, skeletal muscle constructs were transferred into the bioreactor and further cultured for 13 days, while experiencing a stretching pattern adapted from the literature to resemble mouse development and growth. Sample withdrawal occurred at the onset of cyclic stretching and after 7 and 10 days. Myosin heavy chain (MHC) accumulation in stretched constructs (D) was evaluated by Western blot analysis and immunofluorescence staining, using statically cultured samples (S) as controls. RESULTS: Western blot analysis of MHC on dynamically (D) and statically (S) cultured constructs at different time points showed that, at day 10, the applied stretching pattern led to an eight-fold increase in myosin accumulation in cyclically stretched constructs (D) with respect to the corresponding static controls (S). These results were confirmed by immunofluorescence staining of total sarcomeric MHC. CONCLUSIONS: Since previous attempts to reproduce skeletal myogenesis in vitro mainly suffered from the difficulty of driving myoblast development into an architecturally organized array of myosin expressing myotubes, the chance of inducing MHC accumulation via mechanical conditioning represents a significant step towards the generation of a functional muscle construct for skeletal muscle tissue engineering applications.

Cyto- and hemocompatibility of a biodegradable 3D-scaffold material designed for medical applications.

In this study, the polyester urethane Degrapol (DP) was explored for medical applications. Electrospun DP-fiber fleeces were characterized with regard to fiber morphology, swelling, and interconnectivity of interfiber spaces. Moreover, DP was assayed for cell proliferation and hemocompatibility being a prerequisite to any further in vivo application. It was shown that DP-fiber fleeces produced at different humidity while spinning affects interconnectivity of interfiber spaces, such that the higher the humidity the looser the resulting fiber fleeces. When the spinning target was cooled with dry ice, the resulting DP-fibers remained less fused to each other. However, permeability for fluorescent beads was not significantly increased. Fibroblast adhesion and proliferation occurred in a comparable manner on native as well as on fibronectin or collagen I adsorbed DP-fiber fleeces. On DP-surfaces fibroblasts proliferated equally well as compared with glass or PLGA surfaces or DP-surfaces adsorbed with fibronectin or collagen I. In contrast, human umbilical vein endothelial cells proliferated only after adsorption of DP-surfaces with fibronectin or collagen I, indicating that different cell types respond differently to DP-surfaces. Furthermore, hemocompatibility of DP-surfaces was found to be similar or better to PLGA or stainless steel, both medically used materials. These experiments indicate that DP-fiber fleeces or surfaces might be useful for tissue engineering.

Morphologic features of biocompatibility and neoangiogenesis onto a biodegradable tracheal prosthesis in an animal model.

We evaluated a newly designed bioresorbable polymer (Degrapol) tracheal prosthesis in an in-vivo angiogenesis-inducing animal model focusing on the specific tissue reaction, the neo-angiogenesis and also the eventual cathepsin B role during the polymer degradation. Fifteen rabbits were divided into three groups (2, 6 and 8 weeks) and our tube-shaped porous prosthesis was implanted using the common carotid artery and the internal jugular vein as vascular pedicle. Optical and electron microscopy, immunohistochemistry and immunocytochemistry were performed at the end of each period, showing cells and fibrils, in direct contact with the Degrapol scaffold, strongly increased with time. Blood vessel neoformation was visible with CD31 expression localized at the endothelial cells forming the neovascular walls. Over time many of them differentiate in muscle fibers as validated by the expression of alpha-smooth muscle actin (SMA). Few inflammatory cells, expressing CD14, were visible while most cells adopting a pronounced spreading phenotype showed a strong positivity for cathepsin B. We concluded that this bioresorbable polymer provided a good substrate for fibrous tissue deposition with an excellent degree of neo-angiogenesis. Also, cathepsin B seems to contribute to the polymer degradation and particularly to neovascularization by stimulating capillary-like tubular structures and cell proliferation.

Structural variants of biodegradable polyesterurethane in vivo evoke a cellular and angiogenic response that is dictated by architecture.

The aim of this study was to investigate an in vivo tissue response to a biodegradable polyesterurethane, specifically the cellular and angiogenic response evoked by varying implant architectures in a subcutaneous rabbit implant model. A synthetic biodegradable polyesterurethane was synthesized and processed into three different configurations: a non-porous film, a porous mesh and a porous membrane. Glutaraldehyde cross-linked bovine pericardium was used as a control. Sterile polyesterurethane and control samples were implanted subcutaneously in six rabbits (n=12). The rabbits were killed at 21 and 63 days and the implant sites were sectioned and histologically stained using haemotoxylin and eosin (H&E), Masson's trichrome, picosirius red and immunostain CD31. The tissue-implant interface thickness was measured from the H&E slides. Stereological techniques were used to quantify the tissue reaction at each time point that included volume fraction of inflammatory cells, fibroblasts, fibrocytes, collagen and the degree of vascularization. Stereological analysis inferred that porous scaffolds with regular topography are better tolerated in vivo compared to non-porous scaffolds, while increasing scaffold porosity promotes angiogenesis and cellular infiltration. The results suggest that this biodegradable polyesterurethane is better tolerated in vivo than the control and that structural variants of biodegradable polyesterurethane in vivo evoke a cellular and angiogenic response that is dictated by architecture.

Characterization of a slowly degrading biodegradable polyester-urethane for tissue engineering scaffolds.

The purpose of this research was to develop and characterize a novel, slowly degrading polyester-urethane. In this study, a polyester-urethane with a crystalline segment of poly((R)-3-hydroxybutyric acid)-diol linked by a diisocyanate to an amorphous segment of poly(epsilon-caprolactone-co-glycolide)-diol was synthesized. Porous and nonporous scaffolds were processed using electrospinning and solvent casting respectively. The morphology, pore size, and filament diameter of the mesh and film were characterized using scanning electron microscopy (SEM). The thermal properties were examined using differential scanning calorimetry (DSC). A degradation study was initiated to characterize the change in mechanical properties, molecular weight, and surface morphology over 12 months using tensile testing, gel permeation chromatography (GPC), and SEM respectively. Concomitantly, cell morphology and viability on these variants were investigated using fibroblasts. The mechanical test data indicated a gradual decrease in the ultimate tensile strength and strain to break while the modulus of elasticity remained stable. GPC data suggested a slow decrease in the molecular weight while SEM examination revealed changed surface morphologies. The in vitro studies implied that the novel polyester-urethane was not cytotoxic and that the mesh was a more favorable scaffold towards cell viability. The summation of these results suggests that this polyester-urethane has the potential for tissue engineering applications.

Accelerated angiogenesis by continuous medium flow with vascular endothelial growth factor inside tissue-engineered trachea.

OBJECTIVE: To test the effects of a continuous medium flow inside DegraPol scaffolds on the reepithelialization and revascularization processes of a tissue-engineered trachea prosthesis. METHODS: In this proof-of-principle study a continuous medium flow was maintained within a tubular DegraPol scaffold by an inserted porous catheter connected to a pump system. The impact of the intra-scaffold medium flow on the survival of a tracheal epithelial sheet wrapped around and on chondrocyte delivery to the DegraPol scaffold was studied. In the chick embryo, chorioallantoic membrane (CAM) model angiogenesis within the biomaterial was investigated. RESULTS: Scanning electronic microscopy (SEM) images showed an intact epithelial layer after a 2-week support by continuous medium flow underneath. On histology, three-dimensional cell growth was detected in the continuous delivery group. The CAM assay showed that angiogenesis was enhanced within the DegraPol scaffolds when vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) was added to the perfusate. CONCLUSIONS: Taken together, these results demonstrated that the built-in perfusion system within DegraPol scaffolds was able to maintain an intact tracheal epithelial layer, allowed a continuous delivery of cells, and kept an efficient VEGF/VPF expression level which accelerated angiogenic response in the CAM assay. This design combines the in vitro and in vivo parts of tissue engineering and offers the possibility to be used as an in vivo bioreactor implanted for the tissue-engineered reconstruction of trachea and of other organs.

Surface-textured PEG-based hydrogels with adjustable elasticity: Synthesis and characterization.

Poly(ethylene glycol)-dimethacrylate (PEGDMA)-based hydrogels with adjustable shear modulus within the range of 10kPa to 1MPa and precisely predefinable surface textures on a micro-scale were made. It was observed that the volume of all hydrogels after preparation almost exactly matched the volume of the precursor solution and that there were only slight volume changes upon equilibration in excess solvent. This characteristic swelling behavior enables the preparation of textures on the hydrogel's surface with precisely predefinable dimensions. The behavior can be modeled with the Flory-Huggins theory assuming a concentration-dependent polymer-solvent interaction parameter. Additionally, activation of the hydrogels by electrophilic oxirane groups creates reactive sites that will enable the later grafting of the hydrogel's surface with various specific nucleophiles, e.g. biomolecules. Thus, these hydrogels are particularly suitable as biomaterials for systematic investigations of cellular response to surface topography and elasticity of the substrate, both in vivo and in vitro.

Polyesterurethane foam scaffold for smooth muscle cell tissue engineering.

Reconstruction of the genitourinary tract, using engineered urological tissues, requires a mechanically stable biodegradable and biocompatible scaffold and cultured cells. Such engineered autologous tissue would have many clinical implications. In this study a highly porous biodegradable polyesterurethane-foam, DegraPol was evaluated with tissue engineered human primary bladder smooth muscle cells. The cell-polymer constructs were characterized by histology, scanning electron microscopy, immunohistochemistry and proliferation assays. Smooth muscle cells grown on DegraPol showed the same morphology as when grown on control polystyrene surface. Positive immunostaining with alpha smooth muscle actin indicated the preservation of the specific cell phenotype. Micrographs from scanning electron microscopy showed that the cells grew on the foam surface as well as inside the pores. In addition they grew as cell aggregates within the foam. The smooth muscle cells proliferated on the Degrapol; however, proliferation rate decreased due to apoptosis with time in culture. This study showed that Degrapol has the potential to be used as a scaffold.

Electrospun degradable polyesterurethane membranes: potential scaffolds for skeletal muscle tissue engineering.

Skeletal muscle tissue engineering represents an attractive approach to overcome problems associated with autologous transfer of muscle tissue and provides a valid alternative in muscle regeneration enhancement. The aim of this study was to investigate the suitability, as scaffold for skeletal muscle tissue engineering, of a known biodegradable block copolymer (DegraPol) processed by electrospinning in the novel form of microfibrous membranes. Scaffolds were characterized with reference to their morphological, degradative and mechanical properties. Subsequently, cell viability, adhesion and differentiation on coated and uncoated DegraPol) slides were investigated using line cells (C2C12 and L6) and primary human satellite cells (HSCs). The membranes exhibited absence of toxic residuals and satisfactory mechanical properties (linear elastic behavior up to 10% deformation, E modulus in the order of magnitude of MPa). A promising cellular response was also found in preliminary experiments: both line cells and HSCs adhered, proliferated and fused on differently coated electrospun membranes. Positive staining for myosin heavy chain expression indicated that differentiation of C2C12 multinucleated cells occurred within the porous elastomeric substrate. Together the results of this study provide significant evidence of the suitability of electrospun DegraPol) membranes as scaffolds for skeletal muscle tissue engineering and that they represent a promising alternative to scaffolds currently used in this field.

Tissue engineered cartilage generated from human trachea using DegraPol scaffold.

OBJECTIVE: To date numerous attempts have been undertaken to conquer the challenging problem of reconstructing long segmental tracheal defects, as yet without lasting success. Recently, employing concepts of tissue engineering in animals, cartilage-like constructs were transplanted in vivo. However, both the feasibility of fabricating tracheal replacements and the use of human tracheal chondrocytes (HTC) for tissue engineering are still under investigation. In this study, we optimized isolation and cultivation techniques for human tracheal cartilage, assessing the feasibility of seeding these cells onto a novel, three-dimensional (3-D) polyester-urethane polymer (DegraPol). METHODS: Human tracheal cartilage was harvested from the trachea of lung donors, digested in 0.3% collagenase II, and the condrocytes serially passaged every 7-9 days. Cells were also cultivated over agar plate during the total 6-8 weeks expansion phase. Thereafter, chondrocytes were seeded onto DegraPol (pore sizes 150-200 microm) with a seeding density of 2.4 x 10(7)/ml, and chondrocyte-polymer constructs maintained during in vitro static culture. RESULTS: HTC displayed stable proliferation kinetics in monolayer culture with positive expression of collagen type II. Following polymer seeding, both cellular proliferation and extracellular matrix (ECM) production, as measured by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and glycosaminoglycan assays, continued over extended culture. Active growth of HTC on DegraPol was further demonstrated by Alcian blue staining, with the histomorphological appearance of the construct resembling that of native cartilage. Scanning electron microscopy showed chondrocyte growth and ECM synthesis both on the surface and inside the porous scaffold, with a dense cell layer on the surface of the scaffold and a lower cell distribution in the scaffold's interior. CONCLUSIONS: The harvested chondrocytes from human trachea cartilage expand well in vitro and possess the ability to form new cartilage-like tissue when seeded onto DegraPol matrix. However, improved culture conditions are needed to permit cellular growth throughout cell-polymer constructs.

[Spontaneous and induced metamorphosis inXenopus larvae at low temperature]. / Spontane und induzierte Metamorphose bei Larven des Krallenfrosches (Xenopus laevis Daud.) im Kälteversuch.

In premetamorphicXenopus larvae mortality is not influenced by lowering the temperature from 22° to 8.5° C, but it rises dramatically below 8.5° C. At 10° C complete inhibition of spontaneous metamorphosis occurs only in premetamorphic larvae; beyond stage 56 cold treatment only delays the metamorphic changes.In cold-arrested premetamorphic larvae thyroxine and TSH elicit metamorphic responses. Since the responding capacity of the larval tissues to thyroxine is not affected, blockage of spontaneous metamorphosis at low temperature must result from the inhibition of the hypothalamic center.