Arbeitskreis
Phytomedizin in den Tropen und Subtropen

Abstracts der Tagung 2001

Unser diesjähriges Arbeitskreistreffen fand im Rahmen des "Deutschen Tropentages" vom 9. - 11.10.2001 in Bonn statt. Dadurch ist es uns gelungen, die Sektion "Management of Biotic Stresses" (Symposium VII) mit der größten Präsentation (5 Vorträge, 21 Poster und 2 PC Demostrationen) zu gestalten. Dieses bedeutete für den Tropentag ein Novum und ist von zahlreichen Teilnehmern/innen sehr begrüßt worden. Daher sollten wir auch für die Zukunft überlegen, uns regelmäßiger an dieser Veranstaltung zu beteiligen, die mittlerweile 6 alternierende Tagungsorte hat (Berlin, Bonn, Göttingen, Hohenheim, Witzenhausen und Zürich). Über das nächste Treffen 2002 werden wir, die Kollegen Drs. Sagenmüller, Kroschel und Hindorf, Sie rechtzeitig in der "Phytomedizin" und auf der Webseite informieren. Heute zunächst erst einmal die Kurzfassungen der präsentierten Beiträge, die ausführlicher im Abstractband der Tagung und auf einer CD-ROM erfaßt sind (Restexemplare im Tagungsbüro: Prof. Becker, Tel.: 0228/734001, e-mail: aci@uni-bonn.de.

H. Hindorf, Bonn

Titel der Abstracts:

• Protected cultivation - an approach to sustainable vegetable production in the humid tropics
• Induced resistance in crops against parasitic weeds
• Comparative analysis of arthropoda impact on leaf litter decomposition in "Rainforestation Farms" on Leyte, Philippines
• Analysis of tomato-infecting whitefly-transmitted geminiviruses in Central America.
• Evidence of establishment of Cotesia flavipes Cameron (Hymenoptera: Braconidae) and its host range expansion in Ethiopia
• Tracheomycosis (Gibberella xylarioides) on coffee (Coffea arabica)
• Application of antagonistic rhizobacteria to control Meloidogyne incognita on tomato
• Identification of conditions under which Phytophthora capsici forms oospores in planta
• Biodiversity and biotechnology: impact on global plant production
• Plant Pathology and the Internet - recent activities and future trends
• Biological control potential of the antagonistic rhizobacteria Rhizobium etli strain G12 toward the root-knot nematode Meloidogyne incognita on different plant hosts
• Activity of extracts from tropical and sub-tropical spices and herbs against plant pathogenic fungi
• Effects of natural products on soil organisms and plant enhancement
• Endophytic bacteria as a new source of biological control agents against fungal pathogens and plant parasitic nematodes
• Biocontrol activity of rhizobacteria against Fusarium wilt on tomato related to induced resistance
• Integrated Pest Management in Africa
• Improvement of banana (Musa spp.) shoot tip culture to promote biotechnology applications in Sub-Saharan Africa
• The economics of pesticide overuse in cotton production in Pakistan
• Host shift of the diamondback moth Plutella xylostella L. in Kenya: Influence of peas as host plant on the parasitoid Diadegma mollipla (Ichneumonidae)
• Ralstonia solanacearum imported to the European Union with young plants of Pelargonium from Kenya
• Erfahrungen mit dem Internetportal "Global Campus 21" im Rahmen des Nord-Süd-Dialogs
• Cell wall degrading enzymes produced in vitro by isolates of Fusarium graminearum differing in virulence
• Varietal resistance against Xanthomonas campestris pv. manihotis (Xcm), the causal agent of the Cassava Bacterial Blight (CBB)
• Integrated control of cassava bacterial blight: transfer of research results to NARS in Africa and adaptation of control measures to specific agro-ecological conditions

Protected cultivation - an approach to sustainable vegetable production in the humid tropics

A collaborative project of the Faculty of Horticulture, Hannover University, the Institute for Plant Diseases at Bonn University, the Asian Institute of Technology, Bangkok, Thailand, and the Kasetsart University, Bangkok, Thailand is funded by the German Research Foundation (DFG), the German Ministry for Economic Co-operation and Development (BMZ), the University of Hannover and the Federal State of Lower Saxony.
At present vegetable production in South East Asia is characterised by a strong dependency on chemical plant protection, with all the inherent environmental and health hazards for farmers and consumers. In our collaborative project on protected cultivation we therefore intend to develop through a holistic research approach an environmentally friendly, and sustainable vegetable production system for the humid tropics, using tomatoes as model crop. Protected cultivation systems will permit crop production also during the rainy season where field grown vegetables are often completely destroyed by heavy rainfall. Moreover, protected cultivation will enable us to develop and implement various techniques of biological plant protection such as releases of beneficials for pest and disease control. Hence we believe that our approach will permit us to successfully combine both fundamental and applied research, and will lead to the development of a model for a modern vegetable production system in the humid tropics that is both sustainable and less harmful for the environment.

Induced resistance in crops against parasitic weeds

The holoparasitic weed Orobanche cumana is a serious threat for sunflower (Helianthus annuus) cultivations in Eastern and Southern Europe as well as in Western Asia. So far neither common control methods of the pathogen nor breeding for resistance in sunflower proved to be successful.
In recent years there is evidence that the use of specific chemicals, like benzothiodiazole, may activate the resistance in plants based on the principle of systemic acquired resistance (SAR). This proved to be very efficient for several cereals and their bacterial or fungal pathogens, but was never used in sunflower nor in parasitic flowering plants.
Treatments of sunflower seeds with 40 ppm of the resistance inducing chemical benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) for 36 h completely prevented infection in root chambers. In pot trials using 2,86 x 10-4 g Orobanche seeds per g soil as inoculum the total number of O. cumana was reduced to 84 and 95 % in the 60 ppm BTH treatment in the first and second trial, respectively. Corresponding to the concentrations of BTH there was an increasing production of secondary metabolites in the sunflower roots. The functions of these compounds are defence related as well as antioxidative.
The data show that the phenomenon of induced resistance is not restricted to viral, bacterial and fungal disease and demonstrate the great benefit of this protection strategy as an effective component of future plant production systems.

Comparative analysis of arthropoda impact on leaf litter decomposition in "Rainforestation Farms" on Leyte, Philippines

On two different sites concerning altitude, soil and former use, but all under reforestation using the innovative "rainforestation technology", the function of leaf litter arthropoda within the decomposition process was investigated from May to September 2000.
Two different reforestation sites, replanted with indigenous or long time locally adapted forest tree species, have been compared with a reference site in a natural secondary rainforest.
One site, called Punta, is characterized by limestone and low altitude, the other, called ViSCA, by basaltic rocks and higher altitude.
Litter bag trapping of arthropodes showed dominance of mites and collembolans. Ants seem to play also an important role. Higher arthropoda diversity in the leaf litter increased with tree species diversity and variety of available microhabitats.
The feeding activity of the leaf litter fauna was revealed by the Baites Lamina Test Method (Törne,1990). Lowest site specific feeding activity was found at the reference site in the secondary forest. A preliminary analysis of turn-over rates of the leaf litter during 130 days indicates a higher decomposition rate at the secondary forest reference site than in any of the other sites under investigation.
With these preliminary results concerning the impact of arthropoda on leaf litter decomposition on different reforestation sites in the humid tropics a contribution can be made to the knowledge about decomposition and turn-over rates in leaf litter of regnerating former forested aeas.

Analysis of tomato-infecting whitefly-transmitted geminiviruses in Central America.

Tomato yields from fields and greenhouses are often reduced due to viral infection. In many cases geminiviruses have been identified as the viral agent causing these diseases. Geminiviruses are small plant viruses with circular single-stranded DNA (ss-DNA) genomes encapsidated in twinned particles. Members have been divided into four genera on the basis of their genome organisation and host range. Members of the genus Begomovirus infect dicotyledonous plants, are whitefly-transmitted and have bipartite genomes (DNAs A and B).
Until recently, tomato plants grown in Central America were not known to be seriously affected by geminiviruses. This has changed during the last few years. Geminivirus-associated epidemics are currently threatening tomato production in Central America (e.g. Mexico, Puerto Rico and Costa Rica) and the southern United States. Geminivirus-like symptoms were observed in tomatoes in Panama central provinces since 1983 but infections became a problem in 1991 with the increase of whitefly populations due to insecticide misuse. Yield losses of industrial tomatoes were estimated at 2 metric tons during 1991-92 and 1992-93. The outbreak 1996-1997 produced yield losses of more than 3 metric tons. The total losses for tomato growers were equivalent to about 1 million US$ during the period 1991-1997 on the industrial tomato harvest.
We have cloned and sequenced the causal agent, the bipartite Begomovirus tomato leaf curl virus (ToLCV/Pan). For the last four years samples of infected tomatoes and wild plant species were collected and analysed. This survey let to the identification of several distinct tomato-infecting geminiviruses.

Evidence of establishment of Cotesia flavipes Cameron (Hymenoptera: Braconidae) and its host range expansion in Ethiopia

About 29 % of the cereal production in Ethiopia is covered by maize and sorghum. Both crops are first and second in terms of yield per hectare. However, the yield obtained by these crops in the country is half below the world average. One of the major constraint resulting in low yield is the ravage by cereal stemborers which accounts for 20-50 % grain losses. Complex of stemborers attack maize and sorghum in Ethiopia. The major species are Chilo partellus, Busseola fusca, Sesamia calamistis, S. nonagrioides botanephaga, Rhynchaenus niger and Pissodes dubius. The last three species were discovered in the survey made in Ethiopia in 1999 and 2000, while the occurrence of the first three in Ethiopia were reported sometimes before 1970. More than 20 parasitoid species, 10 predators and several entomopathogens are associated to cereal stemborers in Ethiopia. These natural enemies of stemborers attack different stages of the stemborers. However, the role played by larval parasitoid, C. flavipes, in suppressing the population of cereal stemborers is very unique. The parasitism by C. flavipes ranges between 20-90 %. The level of parasitism varies with the variation of stemborer species and other physical factors such as temperature and relative humidity.

Tracheomycosis (Gibberella xylarioides) on coffee (Coffea arabica)

Tracheomycosis is a typical vascular disease syndrome of coffee incited by a fungal pathogen, Gibberella xylarioides (Fusarium xylarioides). The fungus was earlier reported to be a well-known pathogen of other Coffea species in West and Central Africa in the 1950s. The disease was observed again in Zaire (Congo) in the early 1980s and noticed for the first time in Uganda in 1993, it is now causing economic losses on Robusta coffee in both countries. In Ethiopia, the occurrence of G. xylarioides on C. arabica was established in the early 1970s. More recently, systematic surveys of tracheomycosis were conducted in coffee fields with known wilt disease history in some localities of southwestern Ethiopia. All coffee trees in each sample field were diagnosed for external and internal symptoms, and the fungal fruiting bodies were also examined. The assessment was accompanied by sample collection for isolation and identification of the causative agents in the laboratory. The most typical characteristic symptom of infection on mature trees and young coffee seedlings is partial (unilateral) wilting. Internally, dark reddish (brown) discoloration is commonly exhibited on the wood after gently scratching the bark of diseased plants.
The mean disease incidence ranged from 45 % at Gera to 69 % at Bebeka, with certain variations between coffee fields at each locality. The fungus was identified from most of the sample components, and a large number of sexual and asexual spores were also observed from fruiting bodies collected in the field. This survey along with the earlier works implicated that tracheomycosis develops to an important disease on Arabica coffee, too. One of the speculations for the cause of its reemergence in Congo is that aggressive strains of the pathogen may have arisen. In this case, there was no wilt disease on some Robusta coffee in Ethiopia, conversely Arabica coffee has not been affected in Congo and Uganda during the recent outbreaks. Thus further collaborative investigations are being underway in order to contain and manage the disease sustainability. These are comparisons of G. xylarioides isolates from Arabica and Robusta coffee, including earlier isolates of the 1970s; using morphological, genetical and molecular markers; accompanied by proving host specialization of the pathogen on Arabica and Robusta coffee.

Application of antagonistic rhizobacteria to control Meloidogyne incognita on tomato

Identification of conditions under which Phytophthora capsici forms oospores in planta

Phytophthora capsici Leonian is a heterothallic Chromistan plant pathogen in the subtropics and tropics. It causes diverse diseases of least 48 host taxa, and is most damaging during periods of high rainfall. The pathogen is comprised of three genetically and pathogenically distinct subgroups, CAP 1, CAP 2 and CAP 3. Only CAP 1 strains affect herbaceous hosts such as squash, Cucurbita pepo L., and pepper, Capsicum annuum L.
Oospore formation is a most important step in the life cycle of members of the CAP 1 subgroup. Unlike CAP 2 and CAP 3 isolates, CAP 1 isolates do not form chlamydospores. Thus, oospores are the primary survival structures for the CAP 1 subgroup. In addition, because meiosis occurs in the fertilized oogonium, new pathogenicity and fungicide resistance phenotypes can be generated during the formation of these propagules.
In previous work, both the A1 and A2 mating types of P. capsici were present in squash fields that we assayed in South Florida. To further investigate the potential for oospore formation, we examined the conditions under which this event occurred. In studies with detached pepper leaves and a highly fertile pair of A1 and A2 isolates, free moisture was shown to be a key factor in oospore formation. Optimum production occurred only when leaves were immersed or in constant contact with water, and few or no oospores formed under intermittent mist, in closed plastic bags or on wire screens over water reservoirs. Time and temperature were also important factors. Maximum production occurred after 8 days at 18^o C. Production also occurred at 16, 20 and 26^o C, but not at 6, 12 and 32^o C. Very few oospores were formed on intact pepper plants under continuous mist in a glasshouse (ca. 28^o C). Although the potential for oospore formation clearly exists in the studied production areas, our results indicate that the conditions under which oospores of P. capsici form are somewhat specific.

Biodiversity and biotechnology: impact on global plant production

Worldwide approximately 75 000 edible plants exist, 7 000 among these are of nutrition purposes, 20 are intensively used and 5 have changed the world during the past century (China bark, sugar, tea, cotton, potato). The 5 main crops of today and the next 30 years are: wheat, maize, soybean, rice and oilseed rape. The quality of those crops has to be protectd and improved. In 2001 more than 70 transgenic plants were registered worldwide. These include cotton, chicory, potato, squash, maize, soybean, oilseed rape, papaya, tobacco, tomato and carnations. Indeed 45 Mill. ha are actually cultivated with genetically modified plants. 1017 pairs of nucleotids comprising the basic components of life: cytosin, adenin, guanin and thymin represent the total diversity of all beings. This diversity provides the raw as well as the genetic material of the total agricultural production and thereby the nutrition of the world population. Biotechnology / green genetic engineering provides a new instrument for supporting effective agriculture at long term. Finally this represents a new arrangement of resources - even of genetic resources - in compliance with the Agenda 21. The life protecting and long term use of biodiversity is a duty of vital importance for total mankind.

Plant Pathology and the Internet - recent activities and future trends

In recent years the information made available through the internet exploded. As a user it is difficult to keep the track or to decide between high and low quality websites.
For plant pathology the internet became an invaluable tool to communicate and to exchange information. This is due to the fact that information is available without any delay all over the world and everybody can access it (unless the use is restricted). Major advantages of the internet in the field of plant pathology can be concluded for diagnosis, risk assessment, forecasting and alerting services. Beside these tools for practioneers a major impact of the internet can be seen for new interactive teaching and learning plat forms. True online Journals and Conferences will be created and last but not least e-commerce and web portals. Agriculture and Plant Pathology as part of it will use the internet extensively as the tool for exchanging information and for communication.
Disease Alerting services will be a major focus in the near future. The traditional ways of communication by phone or fax will be taken over by the internet and combinations of internet and mobile phone technologies (e.g. SMS).
CD-ROM based services will also switch to internet based tools or as a combination of it. The "Crop Protection Compendium" from CAB International was developed in this way. Today it is available on CD-ROM or via Internet and one of the major information resources world-wide in the field of plant pathology.
But maybe teaching and learning will undergo the most dramatic changes. Will the use of interactive internet-based plat forms overcome the traditional ways of teaching and learning? In this context a new kind of globalisation could take place. Study in one country and living in another.
The Plant Pathology Internet Guide Book (PPIGB):http://www.pk.uni-bonn.de/ppigb/
The Crop Protection Compendium: http://www.cabi.org/compendia.asp

Biological control potential of the antagonistic rhizobacteria Rhizobium etli strain G12 toward the root-knot nematode Meloidogyne incognita on different plant hosts

Species of the root-knot nematode, Meloidogyne, causes high loses to cultivated crops on a world-wide basis, especially in warmer climatic regions and on sandy soils. The nematode is a major pest problem in crop production in most Mediterranean countries and in newly reclaimed desert areas in Egypt. In this study we investigated the influence of plant species on the antagonistic activity of the rhizobacteria biological control agent R. etli G12 toward the root-knot nematode M. incognita. The crops tested included: tomato, cucumber, cotton, soybean and pepper. The effect on the root gall-index, the total number of galls and the number of egg masses of M. incognita on all the crops treated with the biological control agents when compared with the bacteria untreated control plants was measured. The results showed that plant species definitely affects the ability of the rhizobacteria to reduce nematode infection. The rate of reduction varied with crop tested. The level of biological control on the different plants as measured by galling-index from 50 to 17 %. The level of control measured as number of galls varied between 47 and 39 %, whereas the reduction in the number of egg masses varied from 63 to 37 % depending on plant species. The variation in the level of biological control may be due to (1) differences in host-bacteria compatibility caused by differences in root exudate makeup that either favours or disfavours bacterial colonisation (2) to differences in root growth behaviour between the crops tested or (3) to the presence of absence of the ability of the bacteria to produce induced resistance signal in the different plant species. The results demonstrated that host plant can strongly influence the biological control activity of the rhizobacteria R. etli G12 and that pre-screening of crops is necessary to determine biological control efficacy.

Activity of extracts from tropical and sub-tropical spices and herbs against plant pathogenic fungi

Spices and herbs in nature contain different bioactive substances promoting human welfare in various forms since ancient periods. But there is a lack of or only scarce information for the use of spices and herbal extracts in controlling of foliar pathogenic fungi.
23 commercially important spices and herbs were studied like Mentha piperita, Origanum vulgare, Anethum graveolens, etc.. 10 g of pulverised spices and herbs were mixed with 100 ml of 70 % ethanol to extract active compounds in warm water bath at 60 °C for 2 hours. The pellet and supernatants were separated by hydraulic filtration and supernatants utilised for various in vitro and in vivo experiments. In vitro screening of extracts (1% m/v) on PDA against conidial germination of Cladosporium cucumerinum, Botrytis cinerea and Alternaria solani revealed that there was great variability in antifungal natures of the tested preparations. High levels of fungicidal activity (50 to 100%) in inhibition of conidial germination were attained by using extracts from Mentha piperita, Coriandrum sativum, Piper nigrum, Carum carvi and Urtica dioica. Extracts of P. nigrum and U. dioica showed high degree of mycelial growth inhibitory effects on C. cucumerinum and A. solani.
Spices and herbal extracts were screened against A. solani, Phytophthora infestans and Oidium lycopersicum on tomatoes; Erysiphe graminis f. sp. tritici on wheat and Uromyces appendiculatus on bean cotyledons. In most studied cases, extracts of P. nigrum, C. carvi, U. dioica, Cassia spp. and F. vulgare showed significant levels of disease protection activities. An activity guide substance of P. nigrum seed extract was further isolated, identified and characterised with the aid of TLC and HPLC analysis. Hence, the study enabled that detection of an alkaloidal active ingredient from spices and herbs to assist environmentally safe ways in the management of fungal pathogens.

Effects of natural products on soil organisms and plant enhancement

TerraPy^®, Magic Wet^® and Chitosan are soil and plant revitalizers based on natural renewable raw materials. These products stimulate microbial activity in the soil and promote plant growth. Their importance to practical agriculture can be seen in their ability to improve soil health, especially where intensive cultivation has shifted the biological balance in the soil ecosystem to high numbers of plant pathogens. The objective of this study was to investigate the plant beneficial capacities of TerraPy, Magic Wet and Chitosan and to evaluate their effect on bacterial and nematode communities in soils. Tomato seedlings (Lycopersicum esculentum cv. Hellfrucht Frühstamm) were planted into pots containing a sand/soil mixture (1:1, v/v) and were treated with TerraPy^®, Magic Wet^® and Chitosan at 200 kg/ha. At 0, 1, 3, 7 and 14 days after inoculation the following soil parameters were evaluated: soil pH, bacterial and fungal population density (cfu/g soil), total number of saprophytic and plant-parasitic nematodes. At the final sampling date tomato shoot and root fresh weight as well as Meloidogyne infestation was recorded. Plant growth was lowest and nematode infestation was highest in the control. Soil bacterial population densities increased within 24 hours after treatment between 6-fold (Magic Wet) and 25-fold (Chitosan). Bacterial richness and diversity were not significantly altered. Dominant bacterial genera were Acinetobacter (45.1 %) and Pseudomonas (24.4 %) for TerraPy; Pseudomonas (28.9 %) and Acinetobacter (24.6 %) for Magic Wet; Pseuodomonas (83.2 %) for Chitosan and Bacillus (40.4 %) and Pseudomonas (31.6 %) in the control. Increased microbial activity also was associated with higher numbers of saprophytic nematodes. The results demonstrated the positive effects of natural products in stimulating soil microbial activity and thereby the antagonistic potential in soils leading to a reduction in nematode infestation and improved plant growth.

Endophytic bacteria as a new source of biological control agents against fungal pathogens and plant parasitic nematodes

Biocontrol activity of rhizobacteria against Fusarium wilt on tomato related to induced resistance

The fungal wilt pathogen Fusarium oxysporum f. sp. lycopersici causes severe economic losses in horticultural production world-wide. Control of this disease has been accomplished to some extent by resistance in some crops and in most cases with methyl bromide soil fumigation, the latter to be officially banned in the near future. In previous work new microbial antagonists used to enhance transplants for disease control have been identified. Studies on the mode-of-action of these effective rhizobacteria are essential for optimal formulation and practical application to planting material. Six antagonistic bacterial strains were investigated for antagonism toward F. oxysporum f. sp. lycopersici on tomato. In greenhouse experiments plants treated with Pseudomonas fluorescens, P. putida and Bacillus sphaericus before infection with F. oxysporum f. sp. lycopersici showed significantly less wilting and had higher shoot weights as compared to the untreated plants.
To investigate resistance induction, separated application of pathogen and antagonist was achieved by split-root experiments and also by injection of F. oxysporum f. sp. lyco­persici into the stem while the bacteria are applied on the roots. Disease development after injection of F. oxysporum f. sp. lycopersici in plants, whose roots are treated with B. sphaericus, is significantly reduced when compared to untreated infected plants. This may suggest induction of resistance to F. oxysporum f. sp. lycopersici by this isolate. Bacteria-induced changes in plant metabolism were analysed by extraction of phenolic compounds and sepa­ration by Thin Layer Chromatography. Differences in patterns of phenols between treated and untreated plants were detected. Differentially appearing bands are being identified. These changes also indicate a change in plant metabolism related to defense against F. oxy­sporum f. sp. lycopersici.

Integrated Pest Management in Africa

Agriculture in Africa faces unprecedented challenges due to physical (often poor and degrading soils, increasingly frequent droughts or floods, etc.) and biotic stresses (increasing pressure from insect pests, diseases, and weeds). This is the only continent, where per capita food production has not increased in the last 30 years. Productivity increases are often based on expansion of the cultivated area and barely keep pace with population growth. In most countries, about 60-70 % of the population is active in agriculture. Illiteracy and poverty are widespread. In most countries, new land can only be taken into cultivation by encroaching on marginal and/or protected sites. Fallow periods have been reduced, to a degree where soil regeneration is no longer assured. Inputs like fertiliser are badly needed, but often not available or affordable, and the markets are hampered by deficient infrastructure. Given these constraints, how can we best increase productivity on a given surface, and this in a sustainable manner?
Recent research results in plant protection by the International Institute of Tropical Agriculture, in collaboration with other institutions, have provided some adapted and sustainable solutions that have started to improve the livelihood of farming communities. To assure impact, all interventions had been developed and tested with and by farmers. We present several examples of Integrated Pest Management (IPM) options, whose economic and social impact has been or is being assessed and documented. Central innovations concerned: 1.- resistance to diseases (maize streak, cassava mosaic, downy mildew, black sigatoka, etc.), 2.- biological control (mealybugs, mites, floating water weeds, etc.), 3.- sometimes supported by adapted cultural practices (soil improvement, inter or relay cropping, grass bands, etc.), and 4. - development of a commercially produced biocide (Green Muscle^R) against locusts and grasshoppers, which is based on the spores of an entomopathogenic fungus.

Improvement of banana (Musa spp.) shoot tip culture to promote biotechnology applications in Sub-Saharan Africa

In collaboration with the University of Bonn and the Ugandan National Banana Research Programme, the International Institute of Tropical Agriculture (IITA) explores the potential to combine different microbiological control methods to improve plant health of tissue-cultured bananas. The project concentrates on the occurrence and importance of endophytic fungi in banana, but other options are currently being investigated. Endophytic fungi have been reported from many plant species and can be frequently isolated from banana. Fusarium oxysporum was found to be among the more commonly isolated endophytic fungal species from asymptomatic banana rhizomes. The non-pathogenicity of those F. oxysporum strains towards banana and other important crops has been established using pathogenicity tests and genetic markers. Inoculations of some of these strains onto tissue-cultured banana resulted in enhanced plant growth. Nematode and weevil controlling effects were observed in endophyte-inoculated banana plants and pests associated damage was reduced compared to endophyte-free planting material. Endophytes play a pivotal role in this project and it has been shown that they can provide protection to tissue-cultured banana in the first months. However, there is a necessity to integrate other biological control options that target pest and disease problems at later plant stages. Weevil controlling effects of Beauveria bassiana in the field has been reported and will be further verified in farmer's fields. New research will focus on the importance of indigenous strains of Paecilomyces lilacinus for the biological control of banana nematodes in Uganda. The combination of more than one group of biological control agents is expected to further increase the chances of successful and sustainable pest and disease control.

The economics of pesticide overuse in cotton production in Pakistan

The liberalisation of agricultural input markets in Pakistan has resulted in a rapid increase in pesticide use in cotton. While negative externalities of chemical pesticides are meanwhile well documented, that the question of increased pesticide use has significantly contributed to productivity growth remains still unclear. Very often uneconomically high levels of pesticides occured, especially in cotton and lead to the non-sustainability of cotton production. In this study the productivity of pesticides is assessed using the damage control function approach based on data of farm level surveys in Multan district in Punjab. One of our hypothesis was that in an areas with long cotton growing the dependence on pesticides is likely to be higher. Furthermore, health problems as related to pesticides were investigated.
Results showed that in an overuse of pesticides the levels are higher in the area where cotton was introduced recently despite of lower productivity. At the same time health costs are at similar levels, although farmer's knowledge in the area with longer cotton growing were higher. The results challenge some of the conventionally beliefs that pesticide overuse depends on the status of the ecosystem. At the same time the appropriateness of the expected utility theorem, frequently used to explain pesticide overuse, is questioned thus lending some support to the validity of prospect theory in explaining farmer's pesticide use decisions..
This paper challenges one of the sterotypes of agricultural development, frequently repeated by agricultural experts and lobbyists, supporting modern biotechnology in order to increase food production in developing countries. Such goal could only be reached if partnerships with so-called life science companies are established based on an assumed complementarity between public sector and private sector research. Furthermore, the public goods character and the poverty focus of international agricultural research especially of the CGIAR system is generally assumed. In this paper it is shown that the emphasis of development efforts on agricultural producers and the overreliance on the input supply industry as partner has damaged the image of agriculture and is at least partly responsible for the diversion of funds away from agriculture. Contrary to the self-centred complaints about decreasing attention for agricultural productivity increase and the theoretically questionable "underinvestment in agricultural research" hypothesis an alternative approach will be presented. In this approach the focus concentrates on development efforts that start from the consumer rather than from the technology supply site. Particular attention is given to science-based human capacity building through modern approaches of applying information technology for small-scale farmers as an alternative to shifting the yield frontier.

Host shift of the diamondback moth Plutella xylostella L. in Kenya: Influence of peas as host plant on the parasitoid Diadegma mollipla (Ichneumonidae)

The oligophagous diamondback moth (DBM), Plutella xylostella L., is one of the most destructive pests on crucifers worldwide. It is known for its specificity for crucifers and so far, no reports exist about this moth feeding in nature on other plant families. In Central Kenya, in the region of Lake Naivasha, a diamondback moth population shifted to snowpeas (Pisum sativum) causing heavy damage to this crop. This host shift should have an influence on the interaction with natural enemies. One of the most frequent parasitoids attacking the diamondback moth in Kenya is the ichneumonid Diadegma mollipla. In laboratory studies parasitism and growth of D. mollipla reared on pea-DBM compared with DBM feeding on cabbage was measured. Differences in development time, pupal weight, parasitism rates and host preference will be shown.
The study was conducted at the International Center of Insect Physiology and Ecology (ICIPE) in Nairobi integrated into the DBM Biocontrol Project.

Ralstonia solanacearum imported to the European Union with young plants of Pelargonium from Kenya

Recently R. solanacearum, the causal agent of potato brown rot, was introduced with young plants of P. zonale hybr. from Kenya to Germany. Since then, there exists the danger of possible contamination of the domestic potato crop, because the bacterium did not occur so far in Germany. R. solanacearum is a quarantine disease worldwide. The pathogen causes typical wilt symptoms on P. zonale similar to those of another bacterial wilt caused by Xanthomonas campestris pv. pelargonii. With direct infestation or suspicion only, the responsible plant protection measures have to be started. Infected plants should not arrive or being cultivated in the consumer country. Infected plants must be destroyed, responsible officials have to notify the infestation and intensive hygiene measures will start. Measures concerning the country of production, where Ralstonia occurs and represents consequently a danger for the consumer countries, are trade embargoes and limitations. A trade embargo to a member of the European Union involves as well the trade to other states and will cause economic consequences. Therefore, in the status nascendi such a case should be absolutely avoided.

Erfahrungen mit dem Internetportal "Global Campus 21" im Rahmen des Nord-Süd-Dialogs

Der Global Campus 21 (weltweites Lernen im Sinne der Agenda 21) http://www.gc21.de stellt ein internetbasiertes Wissensportal für internationale berufliche Weiterbildung und Nachkontakt dar, welches gemeinschaftlich von der Carl Duisberg Gesellschaft (CDG) und der Deutschen Stiftung für internationale Entwicklung (DSE) aufgebaut wird. Die langfristigen Ziele des Global Campus 21 liegen darin, das lebenslange Lernen ("Lernkontinuum") zu unterstützen, aktuelles Fachwissen zugänglich zu machen, den Austausch zwischen Teilnehmern unterschiedlicher Herkunft und Generation zu verbessern, Netzwerke zu fördern, den Informationsfluß zwischen Teilnehmern, Experten, Partnern und CDG/DSE zu verbessern, sowie ein attraktives und aktuelles Nachkontaktangebot zu gestalten.
Im nicht-öffentlichen Bereich unter "mycampus" besteht für zukünftige, jetzige und frühere Teilnehmer/innen der DSE und CDG die Möglichkeit, z. B. an regionalen und fachlichen Foren, Arbeitsgruppen und Online-Seminaren teilzunehmen, in Gruppen an gemeinsamen Projekten zu arbeiten (shared-work-spaces) oder sich individuell mit Hilfe von Lernprogrammen fortzubilden (web-based-training).
Im Bereich des Pflanzenschutzes hat das Fachzentrum für Ernährung, Ländliche Entwicklung und Umwelt (ZEL) zusammen mit Fachleuten sog. Fachinformationsseiten (FIS) entwickelt, d. h. strukturierte und kommentierte Internetführer zu den Themen: "Legislation in Plant Protection and Plant Quarantine" (Dr. Johann Moltmann, jfm.natkom@t-online.de) und "Natürlicher Pflanzenschutz" (Dr. Martin Baumgart), die für bestimmte Arbeitsgruppen zugänglich sind. Für die Teilnehmer aus Lateinamerika wurde ein Spezialangebot zur Thematik "Ländliche Entwicklung und Management natürlicher Ressourcen" entwickelt. Im Boletín werden u. a. Fachbeiträge zur Entwicklung des integrierten/biologischen Pflanzenschutzes, über Veranstaltungen und Organisationen veröffentlicht. In Verbindung mit dem GC21 steht das von der ZEL und ihren Teilnehmern initiierte und zusammen mit "Internationales Centrum Nord Süd Dialog" (Witzenhausen) betriebene Internet-Netzwerk NECOFA: Netzwerk für nachhaltige Landwirtschaft (ECO-Farming) in Afrika http://www.necofa.org mit eigenem Newsletter.

Cell wall degrading enzymes produced in vitro by isolates of Fusarium graminearum differing in virulence

The relationship between in vitro production of cell wall-degrading enzymes and virulence of 15 Fusarium graminearum isolates were investigated. Enzymatic activities of cellulase, xylanase, and pectinase were measured when F. graminearum isolates were grown in minimum salt medium containing 1 % of cellulose, xylan, and pectin, respectively as the sole carbon source. Cellulase activity was the highest followed by xylanase and finally pectinase. Pectinase activities were detected 2 days after incubation while those of xylanase and cellulase were detected 3-4 days after incubation. The same isolates were examined regarding their virulence on the resistant wheat cultivar 'Arina' and on the susceptible wheat cultivar 'Agent' after a single spikelet inoculation in outdoor pot experiments. All the isolates used were pathogenic (determined by their area under disease progress curve) on both wheat genotypes. Isolates differed significantly in their aggressiveness. There was no correlation between the activities in vitro of the three enzymes and the pathogenicity of the isolates.

Varietal resistance against Xanthomonas campestris pv. manihotis (Xcm), the causal agent of the Cassava Bacterial Blight (CBB)

CBB causes yield losses on cassava (Manihot esculenta) of more than 50 % in African countries. Nine cultivars from Africa and South America were tested under standardized conditions for resistance against a highly virulent strain of Xcm.
By spray-infiltration with 106 cfu/ml typical symptoms were caused on leaves of all tested varieties. Symptom development on the inoculated leaves of a resistant cultivar was delayed by 2-3 days. The disease became systemic within 60 d (wilting, die-back, gumming) on the susceptible cvs., but not on the resistant cv..
Maximum bacterial concentrations of 107 cfu/cm² leaf area (resistant cultivar TMS 30572) and 109 (susceptible cv. Ben 86052) were achieved on young leaves after 6-9 d and on old leaves after 12-15 d.
Systemic spread of bacteria appeared to be impeded in the petioles, especially in the resistant cv.. The resistant cultivar TMS 30572 semmed to be promising in order to reduce losses of CBB in Africa.

Integrated control of cassava bacterial blight: transfer of research results to NARS in Africa and adaptation of control measures to specific agro-ecological conditions

Results of a collaborative EU-financed project, a follow-up of a BMZ-financed research project at IITA (1994-1999), with partners from France (IRD, research group at CIAT, Colombia), United Kingdom (University of Bath), Togo (ITRA, Lome) and Benin (University of Benin) and, as associated partner, IITA, Benin, are presented.
Already achieved research results were transferred to national agricultural research systems (NARS) through collaboration with national partners in Benin and Togo. Field studies under various agronomic and ecological conditions resulted in the identification of locally and regionally well adapted control measures, such as locally preferred, resistant varieties, intercropping with locally used crops, soil amendments with local material, fertilization, and recommendations on sanitary measures to reduce the disease.
Results of European partners were partly verified under African conditions, such as testing of the cassava genome mapping population for reaction towards African strains in order to identify genetic markers and/or resistance related genes. During exchange visits African scientists used techniques elaborated by the European partners, to study specific problems such as primary infection of cassava cuttings, using an antiserum specific for a newly identified pthB protein of Xanthomonas campestris pv. manihotis. Specific molecular detection methods were elaborated and are being transferred to Africa. Microscopic, biochemical and molecular-genetic studies were conducted on mechanisms of resistance, factors of pathogen virulence and host-pathogen interaction.