 |
Phytopathology and Nematology in Soil Ecosystems |  |
|
Phytopathology and Nematology in Soil Ecosystems | |
The broad spectrum of research activities within Soil Ecosystem Pathology are coordinated by Prof. Dr. Richard A. Sikora and Dr. Sebastian Kiewnick with each focusing on his specific research interests (see below).
- Suppressive soils
- Plant parasitic nematodes of tropical and subtropical crops
- Nematicidal activity of fungal culture filtrates
- Biogeography of plant parasitic nematodes in Coffeein Ethiopia
- Endophytic fungi for biological control of plant-parasitic nematodes and foliar
pathogens
(Prof. Dr. Richard A. Sikora, rsikora at server uni-bonn.de)
- Biological control of plant parasitic nematodes with fungal
antagonists
- Production and formulation of antagonistic fungi
- Risk assessment of biocontrol products based on fungal antagonists
- Biological control of Root knot nematodes with Paecilomyces lilacinus strain
251
- Biological control of Aflatoxin producing Aspergillus flavus isolates in Maize
in
Nigeria
(Dr. Sebastian Kiewnick skiewnick at server uni-bonn.de)
Risk assessment of fungal biocontrol agents
The development of biological control products faces several
obstacles before a successful commercialization is achieved. Despite the high public
interest in alternatives to chemical pesticides, the number of biocontrol products,
successfully introduced into the market, is still very low. Although biological control
products demonstrated their ability to efficiently control pests and diseases without
causing any adverse effects to the environment, there are still concerns about the
ecological risks. Evaluating the environmental effects (toxicity and pathogenicity) and
the fate (dispersal and persistence) of the microbial agents is difficult. In addition,
models to appropriately assess exposure are still missing and need to be developed or
modified for microbial pesticides. The nematophagous fungus Paecilomyces lilacinus
strain 251, is our model organism to identify the parameters needed to predict the fate of
fungal biocontrol agents in the environment. To do that, the population dynamic of P.lilacinus
in the soil and rhizosphere is monitored. The effect of application rate, formulation,
temperature, method of application and the presence or absence of the target pest as well
as the host plant on the persistence of P.lilacinus is evaluated.
(Dr. Sebastian Kiewnick)
Biological control of plant parasitic nematodes using Paecilomyces lilacinus strain 251
P. lilacinus strain 251 is a commercially available
biocontrol agent. Recent developments in the mass production and formulation of fungal
biocontrol agents opened new possibilities for this long known antagonist. Our research
group is currently testing the range of activity of this biocontrol agent for control of
plant parasitic nematodes on Tomato, Cucumber, Sugar beet and Banana.
(Dr. Sebastian Kiewnick)
Aflatoxin risk assessment, biological control options and intervention
According to FAO, 25% of the world's food crops are affected by
mycotoxin, which negatively impact human health, food trade, food availability and
consumption. In the developed world, contamination of food and feed is well documented and
food quality is routinely monitored through tens of thousands of analyses, while in Asia,
Africa and South America, mycotoxin analyses do not total 1,000 per year.Most analyses are
done when crops are exported, adding to the overall export costs. Quality assurance
systems for local products are rare, as consumers are unwilling to pay higher costs or are
unaware of the problem. Aflatoxins are chemical metabolites produced by the fungi Aspergillus
flavus, A. parasiticus and A. nominus. They are mutagenic,
carcinogenic, teratogenic and acutely toxic to most animals and humans. The overall goal
of this project is to select atoxigenic (lacking the toxin production) Aspergillus
flavus strains which are then used for biological control of toxin producing Aspergillus
spp..
(Dr. Sebastian Kiewnick)
Use of remote sensing to characterize the spatial and temporal distribution of the sugar beet nematode Ditylenchus dipsaci
Sugar beet nematode Ditylenchus dipsaci has caused a
dramatic damage in sugar beet production areas thoughout Germany. Besides early season
symptoms such as curling and deformation of leaves, severy crown-rot can be observed
towrad the end of the growing season, ultimately leading to complete loss of sugar yield.
In order to investigate the role of biotic and abiotic factor affecting the damage due to
D. dipsaci infestation studies are undertaken to link soil properties suchs as
texture and water content to the damage by this nematode. In addition, remote sensing will
be used to geospatially map plant stress caused by D. dipsaci in sugar beets,
relate spectral reflectance patterns to different nematode densities and to optimize the
biological system management decision making processes to help growers this newly emerged
nematode pest. Currently, tolerant and partially resistant sugar beet cultivars as well as
chemical nematicides are evaluated for their potential to control D. dipsaci.
(Prof. R.A. Sikora and Dr, S. Kiewnick)
Research Training Group of the German Research Foundation No 722
Enhanced efficacy of biological control agents against soil borne plant diseases and nematodes by ecological manipulation
A vascular based disease complex comprised of the root-knot nematode Meloidogyne javanica and the Fusarium wilt pathogen Fusarium oxysporum f. sp. lycopersici causes severe economic losses in vegetable production in the middle east and worldwide (Mai and Abawi, 1987). Control of this disease syndrome has been accomplished for decades only on the basis of methyl bromide soil fumigation. The fumigant which kills 90% of the soil microflora and also stimulates depletion of atmospheric ozone will officially be banned for use in the year 2001. Finding new, effective and environmentaley safe alternative management systems therefore, is a major challenge facing plant pathology. An attempt will be made in the present project to develop new approaches to control the disease complex on tomato by enhancement of antagonistic microorganisms. The objectives of the proposed project are to 1) analyze and enhance the biological control potential of two antagonistic bacteria Pseudomonas fluorescens T58 and Bacillus megaterium 25-6 and the antagonistic Trichoderma harzianum strains T-35 and T-203 to control Meloidogyne/Fusarium, 2) improve formulation and application technology of these biological control agents, and 3) evaluate the impact of these biological enhancements on plant growth, disease severity, and microbial dynamics in natural soil ecosystems.
Use of remote sensing to characterize the spatial and temporal distribution of the sugar beet cyst nematode Heterodera schachtii in sugar beets
Sugar beet cyst nematode Heterodera schachtii is a widespread
pathogen of sugar beets all over the world. Above ground symptoms such as aggregated round
to oval shaped patches of stunted plants are not easily observed at ground level, yet
yields are being reduced. The permanent nature of cyst nematode infestations and their
slow spread within a field was used to develop the predictive computer model - Nemaplot-
that can be used to estimate pre-plant densities over long rotation sequences, to estimate
yield loss and to make cost effective decisions on proper IPM measures at the grow level.
To predict the population development in the field, the initial population density of
Heterodera schachtii is needed. Nematode infested sugar beets have different reflectance
patterns compared to healthy plants. These differences are difficult to detect visually,
but could be detected using remote sensing and GIS technologies. The specific objectives
of this project are to: 1) geospatially map plant stress caused by Heterodera schachtii in
sugar beets 2) relate spectral reflectance patterns to different nematode densities and to
3) optimize the biological system management decision making processes and 4) incorporate
remote sensing data into the Nemaplot program to improve practical uses by the growers,
for example, by reducing costs for specific nematode.
(Prof. R.A. Sikora and Dr, S. Kiewnick)
Research Training Group of the German Research Foundation No 722
Biodiversity of fungal endophytes in banana tissue and practical application of biological control agents against Radopholus similis on banana
Field studies in different agro-ecological zones of Uganda are
conducted to test the biological control potential of endophytic fungi against Radopholus
similis. Several banana germplasms, especially cultivars with resistance against
fungal pathogens, will be tested for their potential to support endopyhtic colonization
and reduce nematode infestation. For suitable host-endophyte systems the endophytic
effects on different stages of the nematode life-cycle will be investigated.
Morphological and physiological investigations on tolerance in the interaction Heterodera schachtii/ sugarbeet
Tolerance of field crops towards plant parasitic nematodes is an
important economic factor. Tolerant plants get less damaged than sensitive ones by
nematode attack and, subsequently, more reliable yields can be achieved. Furthermore,
resistant pathotypes against breeding lines do not emerge with tolerant plants. Since the
underlying mechanisms leading to enhanced tolerance of plants are still unknown, the aim
of our project is 1st to study the plant morphological and physiological basis
for tolerance in the Heterodera schachtii - sugarbeet - interaction and 2nd
to find out tolerance parameters which can be detected in early growing stages and are
correlated positively with yield. In future studies these parameters can contribute to
elaborate molecular markers for an earlier detection of tolerant plants.
Mode-of-action of natural products derived from Basidiomycetes and investigations on the biological control of plant parasitic nematodes with selected strains
The investigations comprise two major parts. First, nematicidal
compounds derived from Basisiomycetes are investigated for new mode-of-actions against
different nematode species. These experiments include studies on vitability, GABA and AchE
receptors. In a second part, greenhouse experiments are carried out to test the
effectiveness of selected strains as biological control agents against Meloidogyne
incognita.
Evaluation and of soil biodiversity in sugarbeet rotations and management of the antagonistic potential to control Heterodera schachtii
A promising method for biological control of H. schachtii is
the promotion of soil biodiversity and thereby of the natural occuring antagonists of the
nematode. The objective of this work is to measure the natural occuring antagonistic
potential in the field and to draw a correlation with the original H. schachtii population.
The general antagonistic potential of field soil will be monitored with various methods.
Main emphasis will be focused on fungal antagonists especially egg pathogenic fungi,
because of their important function of the antagonistic potential. In addition, the effect
of numerous biotic and abiotic factors on the antagonistic potential in field soil will be
measured. After conducting the above experiments, the results will be used to classify
different soils according to their antagonistic potential against H. schachtii.
Biology and life cycle of new cereal cysts nematode species in Syria and examination of associated fungal egg pathogens for control
Cereal cyst nematodes of the genus Heterodera are major pests
of wheat and barley in Syria. The disease is caused by several species like H. avenae,
H. bifenestra, H. mani, H. iri, H. hordicalis and H. latipons. In the past H.
avenae was thought to be the main pathogen. However, recent surveys indicated that
H. latipons is probably the dominant nematode pathogen. The objectives of this project
are to 1) study the biology and life cycle of H. latipons and to 2) evaluate the
antagonistic potential of indigenous fungi, especially the egg parasitic fungi Verticillium
chlamydosprium. The control efficacy of the biocontrol agent will be studied in
different cropping systems under semi-arid conditions.
Biological control of root-knot nematodes on tomato by Pasteuria penetrans
Pasteuria penetrans (Pp) is a specific obligate endoparasite
of different host genera. The bacterial endospores attach to the cuticle of second stage
juveniles (J2), where they germinate after the juveniles have entered the roots and
initiate feeding. The bacterial germ tube penetrates the cuticle and develops into a
vegetative, spherical colony consisting of dichotomously branched, septate mycelium. This
vegetative stage forms then daughter colonies, i.e. doublets and quartets of club-shaped
sporangial while finally develop into endospores. In this study, we are investigating the
effect of seven Pp isolates to control Meloidogyne spp. of two locations. We are
studying different methods to monitor the attachment of Pp spores on J2 of Meloidogyne
spp., and then use the optimal concentration of Pp spores yielding in highest attachment
rate to improve biological control. To gain additional benifits Pp will be applied in
combination with plant growth promoting rhizobacteria (PGPR), Bacillus cereus S18.
The work will focus on analysing the parameters affecting spore attachment such as PGPR
and bacterial culture filtrates, organic matter and compost extract and pesticides such as
nematicides and fungicides.
Rhizosphere specific microbial communities in wheat and importance of root health maintenance
By definition, the rhizosphere is not only the soil surrounding the
root system, it is the soil which is biologically and physiologically influenced by root
exudates. It is a region with intensive biological activities. The extent may vary with
soil type, plant species, age and other factors. Metabolites of plants and microorganisms
are the source of nutrients for the rhizosphere microorganisms. A rhizosphere specific
microbial community (RSMC) develops which may influence plant growth positively or
negatively. So far, 10% of bacteria and 5% of fungi are found to have a positive effect on
plant growth. Different methods have been applied to assess these RSMC, such as the use of
fatty acid analysis, GC-chromatography with the help of Marker fatty acid, detected single
microbial taxa as well as microbial communities in general.
Diversity of bacterial endophyte populations from tomato and their potential for biological control of soil-borne disease and Meloidogyne incognita
Bacterial endophytes are part of natural microflora of healthy
internal plant tissues, and some have been shown to improve plant growth and reduce
disease symptoms caused by several plant pathogens. However, information about their
antagonistic activity towards plant parasitic nematodes is still lacking. The aim of this
project is to test bacterial endophytes isolated from field-grown tomato and potato roots
from Germany and Indonesia, on their antagonistic activity towards Meloidogyne
incognita. Additionally, these bacteria will be tested for their antifungal activity in-vitro
towards Rhizoctonia solani, Fusarium oxysporum sp.f. lycopersici and Fusarium
oxysporum sp.f. radicis-lycopersici. Studies on the mode-of-action of promising
endophytic bacteria will be carried out as well as identification of these endophytes by
fatty acid analysis using FAME-GC-analysis.
Cytological investigations on the spread and development of soil-borne endophytic fungi in barley and their capability to reduce powdery mildew Erysiphe graminis f.sp. hordei
Colonization of plants by endophytic microorganisms can cause changes of the complex defense strategy of plants directed against pathogen attack. The ascomycete Chaetomium globosum has shown to control powdery mildew in barley when applied to the kernels using a spore suspension. Localization studies confirmed the endophytic behaviour of this antagonistic fungus. To understand the mode-of-action of the reduced disease severity the interaction pathogen-plant-endophyte will be cytologically analyzed using immunological markers for the detection of the endophyte in situ.
Cross protection of banana with fungal endophytes for the control of Panama wilt (Fusarium oxysporum f.sp. cubense) in tissue production systems
The main objetive of this research is to find fungal endophytes as
antagonist of Fusarium oxysporum f.sp. cubense. Fungal endophytes were
isolated from roots, corms and leaves of different banana cultivars. Culture filtrates of
fungal endophytes were obtained on 3 different liquid media: potato dextrose broth,
gliotoxin fermentation medium, and Czapek-Dox fermentation medium. These culture filtrates
will be tested in vitro against Fusarium oxysporum f.sp. cubense. The best
fungal endophytes will be used in greenhouse studies for protection of banana plantlets of
four major banana cultivars to control Fusarium oxysporum f.sp. cubense.
Chitosan as biological agent to control Meloidogyne inocgnita
During the last couple of years the demand of effective and environmentaley safe agents to control infection by plant parasitic nematodes has increased enormously. The aim of this project is to test five organic amendments (Chitosan, Oli.H. Oligochitosan, Oli N Oligochitin, Biosol Chitin-Oligo, n =1-7, NaCl) on their capability to control Meloidogyne incognita on tomato. These natural compounds in rate of 0.01 % to 0.1 % will be mixed and shaked with sandy soil in plastic bags and placed in pots. Two days later the soil will be infested with eggs of M. incognita following planting of tomatoes. Besides counting of the incidence of root galling and eggs mass, effects on shoot weight (g), root weight (g), root length (m) of tomato plants will be determined as parameter for enhanced plant health and plant growth.
Nematode resistance and/or tolerance in locally grown cassava cultivars to root-knot nematode species and races
An increasing number of reports has lately stated nematode problems
on cassava. The cassava germplasm collection at IITA Uganda (>1000 lines) was screened
for resistance against viruses but provides almost no information on nematode resistance
or tolerance. In field experiments major breeding lines will be tested for their
susceptibility against Meloidogyne incognita infestation. The projects goal is to provide
farmers with a selection of planting material from resistant to tolerant cultivars which
they can individually use depending on their nematode situation in the field.
Control of the banana corm weevil (Cosmopolites sordidus) with fungal endophytes applied to tissue culture plantlets in Uganda
Mutualistic fungal endophytes isolated from healthy banana stems
have shown antagonistic activity against the banana weevil Cosmopolites sordidus.
Greenhouse and field experiments are conducted to study the endophytic colonization of
these fungi and their potential as biocontrol agents. In addition, different formulation
and application techniques will be tested to improve control efficacy.