Agricultural performance in Tanzania under structural adjustment programs: Is it really so positive?     

Bert Meertens 《Agriculture and Human Values》2000,17(4):333-346

The performances in the food and cashcrop sectors and the availability and consumption ofagricultural inputs in Tanzania during structuraladjustment programs (1986–1996) are compared withperiods prior to this IMF/World Bank backed reform.The positive developments in the first five years ofreform appear to be not sustainable. Presentlyproductivity levels per rural capita for importantfood and cash crops are declining. There are nofurther improvements in the availability andconsumption of agricultural inputs. The removal ofsubsidies on agricultural inputs from 1991 onwards iscrucial in explaining the decline in maize production,the main food crop in Tanzania. Some assumptionsbehind the reform measures are proving to be wrong.Modifications are thus needed to improve theagricultural sector of Tanzania in a sustainable way.Structural adjustment programs usually go too far inreducing the role of the government. However,government involvement might be necessary to ensure ahigher consumption of agricultural inputs and thus abetter performance of the agricultural sector inTanzania. A higher productivity in the agriculturalsector is needed in Tanzania to avoid food securityproblems in the future.  相似文献   

Nematode succession during composting and the potential of the nematode community as an indicator of compost maturity     

Hanne Steel  Eduardo de la Peña  Koen Willekens  Wim Bert 《Pedobiologia》2010,53(3):181-363

One of the key issues in compost research is to assess when the compost has reached a mature stage. The maturity status of the compost determines the quality of the final soil amendment product. The nematode community occurring in a Controlled Microbial Composting (CMC) process was analyzed with the objective of assessing whether the species composition could be used as a bio-indicator of the compost maturity status. The results obtained here describe the major shifts in species composition that occur during the composting process. Compared to terrestrial ecosystems, nematode succession in compost differs mainly in the absence of K-strategists and numerical importance of diplogastrids. At the beginning of the composting process (thermophilic phase), immediately after the heat peak, the nematode population is primarily built by bacterial feeding enrichment opportunists (cp-1) (Rhabditidae, Panagrolaimidae, Diplogastridae) followed by the bacterial-feeding general opportunists (cp-2) (Cephalobidae) and the fungal-feeding general opportunists (Aphelenchoididae). Thereafter, during the cooling and maturation stage, the bacterial-feeding-predator opportunistic nematodes (Mononchoides sp.) became dominant. Finally, at the most mature stage, the fungal-feeding Anguinidae (mainly Ditylenchus filimus) were most present. Both, the Maturity Index (MI) and the fungivorous/bacterivorous ratio (f/b ratio), increase as the compost becomes more mature (ranging, respectively, from 1 to 1.86 and from 0 to 11.90). Based on these results, both indices are suggested as potential suitable tools to assess compost maturity.  相似文献   

Remediation of Metal Contaminated Soil by Organic Metabolites from Fungi I—Production of Organic Acids     

Zandra Arwidsson  Emma Johansson  Thomas von Kronhelm  Bert Allard  Patrick van Hees 《Water, air, and soil pollution》2010,205(1-4):215-226

Investigations were made on living strains of fungi in a bioremediation process of three metal (lead) contaminated soils. Three saprotrophic fungi (Aspergillus niger, Penicillium bilaiae, and a Penicillium sp.) were exposed to poor and rich nutrient conditions (no carbon availability or 0.11 M d-glucose, respectively) and metal stress (25 µM lead or contaminated soils) for 5 days. Exudation of low molecular weight organic acids was investigated as a response to the metal and nutrient conditions. Main organic acids identified were oxalic acid (A. niger) and citric acid (P. bilaiae). Exudation rates of oxalate decreased in response to lead exposure, while exudation rates of citrate were less affected. Total production under poor nutrient conditions was low, except for A. niger, for which no significant difference was found between the poor and rich control. Maximum exudation rates were 20 µmol oxalic acid g^?1 biomass h^?1 (A. niger) and 20 µmol citric acid g^?1 biomass h^?1 (P. bilaiae), in the presence of the contaminated soil, but only 5 µmol organic acids g^?1 biomass h^?1, in total, for the Penicillium sp. There was a significant mobilization of metals from the soils in the carbon rich treatments and maximum release of Pb was 12% from the soils after 5 days. This was not sufficient to bring down the remaining concentration to the target level 300 mg kg^?1 from initial levels of 3,800, 1,600, and 370 mg kg^?1in the three soils. Target levels for Ni, Zn, and Cu, were 120, 500, and 200 mg kg^?1, respectively, and were prior to the bioremediation already below these concentrations (except for Cu Soil 1). However, maximum release of Ni, Zn, and Cu was 28%, 35%, and 90%, respectively. The release of metals was related to the production of chelating acids, but also to the pH-decrease. This illustrates the potential to use fungi exudates in bioremediation of contaminated soil. Nonetheless, the extent of the generation of organic acids is depending on several processes and mechanisms that need to be further investigated.  相似文献   

Metabolic profiling of ‘Conference’ pears under low oxygen stress     

Romina Pedreschi  Christine Franck  Jeroen Lammertyn  Alexander Erban  Joachim Kopka  Maarten Hertog  Bert Verlinden  Bart Nicolaï 《Postharvest Biology and Technology》2009,51(2):123-130

Pears (Pyrus communis L. cv. Conference) may develop core breakdown when stored under low oxygen or elevated carbon dioxide conditions. This physiological disorder is characterized by the development of brown spots due to oxidation of phenolic compounds, and eventually, cavities in the center of the fruit. Based on metabolic profiling of brown and sound tissue using GC-EI-TOF-MS, the hypothesis that this disorder is due to an imbalance between oxidative and reductive processes at the cellular level was investigated. Brown tissue was clearly characterized by a distinctive pattern in changes which included a decrease of malic acid and an increase in fumaric acid and gamma aminobutyric acid (GABA), which indicated a reduced metabolic activity at the level of the Krebs cycle and a putative block of the GABA shunt pathway. Increased gluconic acid concentration might be related to ascorbic acid degradation due to insufficient reducing equivalents or to an impaired pentose phosphate pathway. For the first time, GABA and gluconic acid have been shown to be metabolic markers for core breakdown. The concentrations of other compounds which are believed to be related to hypoxic stress response such as trehalose and putrescine were also considerably higher in brown tissue than in sound tissue. The concentration of some sugars which are typically found in xyloglucans also increased during brown development, possibly indicating cell wall breakdown due to enzymatic processes or chemical reactions of hydroxyl radicals.  相似文献   

Multi-event capture–recapture modeling of host–pathogen dynamics among European rabbit populations exposed to myxoma and Rabbit Hemorrhagic Disease Viruses: common and heterogeneous patterns     

Simone Santoro  Isa Pacios  Sacramento Moreno  Alejandro Bertó-Moran  Carlos Rouco 《Veterinary research》2014,45(1):39

Host–pathogen epidemiological processes are often unclear due both to their complexity and over-simplistic approaches used to quantify them. We applied a multi-event capture–recapture procedure on two years of data from three rabbit populations to test hypotheses about the effects on survival of, and the dynamics of host immunity to, both myxoma virus and Rabbit Hemorrhagic Disease Virus (MV and RHDV). Although the populations shared the same climatic and management conditions, MV and RHDV dynamics varied greatly among them; MV and RHDV seroprevalences were positively related to density in one population, but RHDV seroprevalence was negatively related to density in another. In addition, (i) juvenile survival was most often negatively related to seropositivity, (ii) RHDV seropositives never had considerably higher survival, and (iii) seroconversion to seropositivity was more likely than the reverse. We suggest seropositivity affects survival depending on trade-offs among antibody protection, immunosuppression and virus lethality. Negative effects of seropositivity might be greater on juveniles due to their immature immune system. Also, while RHDV directly affects survival through the hemorrhagic syndrome, MV lack of direct lethal effects means that interactions influencing survival are likely to be more complex. Multi-event modeling allowed us to quantify patterns of host–pathogen dynamics otherwise difficult to discern. Such an approach offers a promising tool to shed light on causative mechanisms.  相似文献   

Spatial and temporal distribution of trunk-injected (14) C-imidacloprid in Fraxinus trees     

Tanis SR  Cregg BM  Mota-Sanchez D  McCullough DG  Poland TM 《Pest management science》2012,68(4):529-536

BACKGROUND: Since the discovery of Agrilus planipennis Fairmaire (emerald ash borer) in 2002, researchers have tested several methods of chemical control. Soil drench or trunk injection products containing imidacloprid are commonly used to control adults. However, efficacy can be highly variable and may be due to uneven translocation of systemic insecticides. The purpose of this study was to determine whether sectored xylem anatomy might influence imidacloprid distribution in tree crowns. RESULTS: Imidacloprid equivalent concentrations were higher in leaves from branches in the plane of the injection point (0°) than in leaves from branches on the opposite side of the injection point (180°). Leaves from branches 90° to the right of injection points had higher imidacloprid equivalent concentrations than leaves from branches 90° to the left of injection points. Leaves and shoots had higher imidacloprid equivalent concentrations than roots and trunk cores, indicating that imidacloprid moves primarily through the xylem. CONCLUSION: Imidacloprid equivalent concentration in leaves varied over time and in relation to injection points. It is concluded that ash trees have sectored ‘zigzag’ xylem architecture patterns consistent with sectored flow distribution. This could lead to variable distribution of imidacloprid in tree crowns and therefore to variable control of A. planipennis. Copyright © 2012 Society of Chemical Industry  相似文献   

An improved breeding strategy for autotetraploid alfalfa (Medicago sativa L.)     

Felicitas M. Katepa-Mupondwa  Bert R. Christie  Thomas E. Michaels 《Euphytica》2002,123(1):139-146

Alfalfa cultivar development will be enhanced by breeding strategies whichutilize the full potential of autotetraploid population genetic structures. Thisstudy evaluates the effectiveness of an allelic selection scheme, which wasdeveloped to overcome limitations of inbreeding depression and to exploitgeneral and specific combining ability effects in autotetraploid populations.Allelic selection entails the minimization of non-additive genetic effects byselecting among full-sib families (F1) which are at uniform levels ofheterozygosity. Such F1 lines are developed by crossing individuals fromtwo unrelated random mating populations. Selected F1 lines wereintercrossed to form an improved population. Eight random matingpopulations of alfalfa were developed to study the effectiveness of allelicselection. Selection for increased dry matter yield resulted in alfalfapopulations with 38 percent greater yield than the parent populations. Twocycles of intercrossing, among selected F1 lines, did not dissipate the gainfrom selection. This result has important implications for synthetic cultivardevelopment in which a major limitation is the decline in productivity withadvancing generations of seed increase. A positively correlated response toselection for dry matter yield was observed for plant height and stemdiameter. The results of this research indicate that continued testing of theallelic selection scheme is warranted and could have a significant impact onthe breeding of autotetraploid alfalfa, particularly for synthetic cultivardevelopment.  相似文献   

Transient gene expression in transformed banana (Musa cv. Bluggoe) protoplasts and embryogenic cell suspensions     

László Sági  Serge Remy  Bert Verelst  Bart Panis  Bruno P. A. Cammue  Guido Volckaert  Rony Swennen 《Euphytica》1995,85(1-3):89-95

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Cultivar identification and genetic relationship among selected breeding lines and cultivars in chickpea (Cicer arietinum L.)     

M.A. Chowdhury  Bert Vandenberg  T. Warkentin 《Euphytica》2002,127(3):317-325

Twenty two RAPD and 22 ISSR markers were evaluated for their potential use in determination of genetic relationships in chickpea (Cicer arietinum L.) cultivars and breeding lines. We were able to identify six chickpea cultivars/breeding lines by cultivar-specific markers. All of the cultivars tested displayed a different phenotype generated either by the RAPD or ISSR primers. Though ISSR primers generated less markers than RAPD primers, the ISSR primers produced higher levels of polymorphism (% of polymorphic markers per primer) than RAPD primers. A high level of within cultivar homogeneity was observed in chickpea. Cultivars/breeding lines originating from a common genetic background showed closer genetic relationship. Chickpea lines with similar seed type(kabuli or desi) had a tendency to cluster together. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Sensitivity of CERES-Maize simulated yields to uncertainty in soil properties and daily solar radiation     

Federico E. Bert  Carlos E. Laciana  Guillermo P. Podestá  Emilio H. Satorre  Angel N. Menéndez 《Agricultural Systems》2007

The sensitivity of CERES-Maize yield predictions to uncertainty in a set of soil-related parameters and solar radiation was evaluated in Pergamino, in the Argentine Pampas. Maize yields were simulated for Pergamino using a 31 years climatic record for a range of values of a group of important model input variables. The input variables considered (and the range evaluated) were: soil nitrogen content at sowing (from 20 to 80 Kg ha⁻¹), soil organic matter content (from 1.75% to 4%), soil water storage capacity (from 150 to 200 mm), soil water content at sowing (from 50% to 100% of total available water), soil infiltration curve number (from 76 to 82) and daily solar radiation (from −20% to 12% of the historical values). Then, a sensitivity analysis using a combination of mathematical and graphical approaches was performed to evaluate the model response to changes in the values of the input variables considered. Moreover, a simplified method based on the evaluation of the model sensitivity at extreme values of the input variables is proposed to evaluate the model non-linear responses with a reduced number of runs. Under the scenario evaluated, representative of the typical maize productions systems of the Argentine Pampas, the model results showed higher sensitivity to changes in radiation (normalized sensitivity were −0.69 and 0.45 for rainfed and irrigated conditions, respectively) than for the soil variables (normalized sensitivity ranged from 0.20 to 0.28). The CERES-Maize model was found to have similar sensitivity for the different soil inputs. Furthermore, some of the variables evaluated (soil curve number, soil water content at sowing and radiation under rainfed conditions) showed an important non-linear response.  相似文献