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The use of the fungus Ascochyta caulina as a biological control agent for the weed Chenopodium album. Evaluation of the bioherbicide formulation efficacy of Ascochyta caulina on different life stages of the weed plant Chenopodium album under laboratory and field conditions comparing Libyan and UK populations.Asshleb, Almabrouk A. January 2010 (has links)
Chenopodium album is considered one of the most important weeds adversely affecting
agricultural production due to its highly competitive influence on field crops. Chemical
herbicides have increased the efficiency of farming, but recently problems of herbicideresistant
weed populations and herbicide residues in soil, water, food products and effects
on non-target organisms have increased, consequently, other methods of control of weeds
by using specific fungi as herbicides have been suggested. The purpose of this research was
to evaluate the biological control of the weed Chenopodium album by the fungus Ascochyta
caulina. Some of the factors which control dormancy and germination of Chenopodium
album seeds have been investigated to understand better the weed population dynamics.
The results showed that seeds from two populations (UK and Libya) differ in their response
to factors such as light, chilling, and burying in soil. This could have implications for
effective control of the weed in different regions.
Two formulations of mycoherbicides (Tween 80 and Gelatine based applications) were
tested in the laboratory, and showed promise in reducing growth of the weed, especially the
formula of Tween 80. There was extensive shoot fresh and dry weight reduction of
inoculated Chenopodium album, as well as reduced root growth. Highest disease severity
rates were observed on plants in the first three week of life. A field trial revealed similar
results but less disease severity was observed, possibly because of dry weather. However, it
was concluded that the fungus Ascochyta caulina is a potentially useful biological control
agent but many factors still can be modified in relation to application of the mycoherbicide
to increase its efficacy. / Libyan Government
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The use of the fungus Ascochyta caulina as a biological control agent for the weed Chenopodium album : evaluation of the bioherbicide formulation efficacy of Ascochyta caulina on different life stages of the weed plant Chenopodium album under laboratory and field conditions comparing Libyan and UK populationsAsshleb, Almabrouk Amer January 2010 (has links)
Chenopodium album is considered one of the most important weeds adversely affecting agricultural production due to its highly competitive influence on field crops. Chemical herbicides have increased the efficiency of farming, but recently problems of herbicideresistant weed populations and herbicide residues in soil, water, food products and effects on non-target organisms have increased, consequently, other methods of control of weeds by using specific fungi as herbicides have been suggested. The purpose of this research was to evaluate the biological control of the weed Chenopodium album by the fungus Ascochyta caulina. Some of the factors which control dormancy and germination of Chenopodium album seeds have been investigated to understand better the weed population dynamics. The results showed that seeds from two populations (UK and Libya) differ in their response to factors such as light, chilling, and burying in soil. This could have implications for effective control of the weed in different regions. Two formulations of mycoherbicides (Tween 80 and Gelatine based applications) were tested in the laboratory, and showed promise in reducing growth of the weed, especially the formula of Tween 80. There was extensive shoot fresh and dry weight reduction of inoculated Chenopodium album, as well as reduced root growth. Highest disease severity rates were observed on plants in the first three week of life. A field trial revealed similar results but less disease severity was observed, possibly because of dry weather. However, it was concluded that the fungus Ascochyta caulina is a potentially useful biological control agent but many factors still can be modified in relation to application of the mycoherbicide to increase its efficacy.
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The Grass Seed Pathogen Pyrenophora semeniperda as a Biocontrol Agent for Annual Brome GrassesStewart, Thomas E. 05 July 2009 (has links)
Bromus tectorum and other annual brome grasses have invaded many ecosystems of the western United States, and because of an annual-grass influenced alteration of the natural fire cycle on arid western range lands near monocultures are created and conditions in which the native vegetation cannot compete are established. Each year thousands of hectares become near monocultures of annual brome grasses. Pyrenophora semeniperda, a generalist seed pathogen of annual grasses, shows major potential as a possible mycoherbicide that could help in reducing the monocultures created by annual grasses. The purpose of this research was to identify the requirements for isolating cultures of P. semeniperda, search for a hypervirulent strain, and evaluate its effect in the field. The techniques for isolating the fungus have evolved and become more efficient. The first two years of working with P. semeniperda resulted in 11 isolates. During the third year of this study, we developed a single spore isolation technique that resulted in 480 additional isolates. Virulence screening resulted in detection of a range of isolate ability to kill non-dormant B. tectorum seeds. Ninety-two isolates represented a range of virulence from 0-44%. The variation in virulence was expressed mostly within populations rather than between populations. Similarly, virulence varied significantly within Internal Transcribed Spacer (ITS) genotypes and habitats but not between them. When conidial inoculum was applied in the field there was no observed difference in disease incidence between different levels of inoculum. This is thought to have been due to applying the inoculum under conditions in which most in situ seeds were infected and killed by already high field inoculum loads. While additional field trials are needed to optimize the inoculum effectiveness, the overall results of this research provide a good foundation for using P. semeniperda as a biological control for seed banks of annual brome grasses.
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A model system using insects to vector Fusarium tumidum for biological control of gorse (Ulex europaeus)Yamoah, Emmanuel January 2007 (has links)
The overall objective of this study was to test the hypothesis that insects can vector F.
tumidum conidia to infect gorse plants with the aim of developing an alternative approach to mycoherbicide delivery to control weeds. Four potential insect species (Apion ulicis, Cydia ulicetana, Epiphyas postvittana and Sericothrips staphylinus) were assessed for their ability to vector F. tumidum conidia. To achieve this, the external microflora (bacteria and fungi) and the size and location of fungal spores on the cuticle of these insect species were determined. In addition, the ability of the insects to pick up and deposit F. tumidum conidia on agar was studied. Based on the results from these
experiments, E. postvittana was selected for more detailed experiments to determine transmission of F. tumidum to infect potted gorse plants. The factors promoting pathogenicity of F. tumidum against gorse and the pathogen loading required to infect and kill the weed were also determined.
The external microflora of the four insect species were recovered by washing and plating
techniques and identified by morphology and polymerase chain reaction restriction
fragment length polymorphism (PCR-RFLP) and sequencing of internally transcribed
spacer (ITS) and 16S rDNA. A culture-independent technique (direct PCR) was also used
to assess fungal diversity by direct amplification of ITS sequences from the washings of the insects. All insect species carried Alternaria, Cladosporium, Nectria, Penicillium,
Phoma, Pseudozyma spp. and entomopathogens. Ninety four per cent of the 178 cloned
amplicons had ITS sequences similarity to Nectria mauritiicola. E. postvittana carried the
largest fungal spores (mean surface area of 125.9 ìm2) and the most fungal CFU/insect.
About 70% of the fungi isolated from the insects were also present on the host plant
(gorse) and the understorey grass. The mean size of fungal spores recovered from the
insect species correlated strongly with their body length (R² = 85%). Methylobacterium
aquaticum and Pseudomonas lutea were common on all four insect species.
Pseudomonas fluorescens was the most abundant bacterial species.
In the pathogenicity trials, the effectiveness of F. tumidum in reducing root and shoot
biomass of 16 and 8 wk old gorse plants was significantly increased with wounding of the
plants. Older plants (32 wk old) which were wounded and inoculated were significantly
shorter, more infected and developed more tip dieback (80%) than plants which were not
wounded (32%). This indicates that damage caused by phytophagous insect species
present on gorse through feeding and oviposition may enhance infection by F. tumidum.
Wounding may release nutrients (e.g. Mg and Zn) essential for conidia germination and
germ tube elongation and also provide easier access for germ tube penetration. Conidial
germination and germ tube length were increased by 50 and 877%, respectively when
incubated in 0.2% of gorse extract solution for 24 h compared with incubation in water.
Inoculum suspensions amended with 0.2% of gorse extract caused more infection and
significantly reduced biomass production of 24 wk old gorse plants than suspensions
without gorse extract. A minimum number of about 900 viable conidia/infection site of F.
tumidum were required to infect gorse leaves. However, incorporation of amendments
(which can injure the leaf cuticle) or provision of nutrients (i.e. gorse extract or glucose)
in the formulation might decrease the number of conidia required for lesion formation.
Scanning electron micrographs showed that germ tube penetration of gorse tissue was
limited to open stomata which partly explain the large number of conidia required for
infection. The flowers and leaves were more susceptible to F. tumidum infection than the
spines, stems and pods. An experiment to determine the number of infection sites
required to cause plant mortality showed that the entire plant needs to be inoculated in
order for the pathogen to kill 10 wk old plants as F. tumidum is a non systemic pathogen.
The number of infection sites correlated strongly with disease severity (R² = 99.3%). At
least 50% of the plant was required to be inoculated to cause a significant reduction in
shoot dry weight. F. tumidum, applied as soil inoculant using inoculated wheat grains in three separate experiments, significantly suppressed gorse seedling emergence and biomass production.
In experiments to determine the loading capacity of the insect species, E. postvittana, the
largest insect species studied, carried significantly more (68) and deposited significantly more (29) F. tumidum conidia than the other species. Each E. postvittana, loaded with 5,000 conidia of F. tumidum, transmitted approximately 310 conidia onto gorse plants but
this did not cause any infection or affect plant growth as determined by shoot fresh
weight and shoot height. E. postvittana on its own did not cause any significant damage
to gorse and did not enhance F. tumidum infection. It also failed to spread the pathogen
from infected plants to the healthy ones. There was no evidence of synergism between the
two agents and damage caused by the combination of both E. postvittana and F. tumidum
was equivalent to that caused by F. tumidum alone.
This study has shown that E. postvittana has the greatest capacity to vector F. tumidum
since it naturally carried the largest and the most fungal spores (429 CFU/insect).
Moreover, it naturally carried Fusarium spp. such as F. lateritium, F. tricinctum and
Gibberella pulicaris (anamorph Fusarium sambucinum) and was capable of carrying and
depositing most F. tumidum conidia on agar. Coupled with the availability of pheromone
for attracting the male insects, E. postvittana may be a suitable insect vector for
delivering F. tumidum conidia on gorse using this novel biocontrol strategy. Although it
is a polyphagous insect, and may visit non-target plants, F. tumidum is a very specific
pathogen of gorse, broom and a few closely related plant species. Hence, using this insect
species to vector F. tumidum in a biological control programme, should not pose a
significant threat to plants of economic importance. However, successful control of gorse
using this "lure-load-infect" concept would depend, to a large extent on the virulence of
the pathogen as insects, due to the large size of F. tumidum macroconidia, can carry only
a small number of it.
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A model system using insects to vector Fusarium tumidum for biological control of gorse (Ulex europaeus)Yamoah, Emmanuel January 2007 (has links)
The overall objective of this study was to test the hypothesis that insects can vector F. tumidum conidia to infect gorse plants with the aim of developing an alternative approach to mycoherbicide delivery to control weeds. Four potential insect species (Apion ulicis, Cydia ulicetana, Epiphyas postvittana and Sericothrips staphylinus) were assessed for their ability to vector F. tumidum conidia. To achieve this, the external microflora (bacteria and fungi) and the size and location of fungal spores on the cuticle of these insect species were determined. In addition, the ability of the insects to pick up and deposit F. tumidum conidia on agar was studied. Based on the results from these experiments, E. postvittana was selected for more detailed experiments to determine transmission of F. tumidum to infect potted gorse plants. The factors promoting pathogenicity of F. tumidum against gorse and the pathogen loading required to infect and kill the weed were also determined. The external microflora of the four insect species were recovered by washing and plating techniques and identified by morphology and polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) and sequencing of internally transcribed spacer (ITS) and 16S rDNA. A culture-independent technique (direct PCR) was also used to assess fungal diversity by direct amplification of ITS sequences from the washings of the insects. All insect species carried Alternaria, Cladosporium, Nectria, Penicillium, Phoma, Pseudozyma spp. and entomopathogens. Ninety four per cent of the 178 cloned amplicons had ITS sequences similarity to Nectria mauritiicola. E. postvittana carried the largest fungal spores (mean surface area of 125.9 µm²) and the most fungal CFU/insect. About 70% of the fungi isolated from the insects were also present on the host plant (gorse) and the understorey grass. The mean size of fungal spores recovered from the insect species correlated strongly with their body length (R² = 85%). Methylobacterium aquaticum and Pseudomonas lutea were common on all four insect species. Pseudomonas fluorescens was the most abundant bacterial species. In the pathogenicity trials, the effectiveness of F. tumidum in reducing root and shoot biomass of 16 and 8 wk old gorse plants was significantly increased with wounding of the plants. Older plants (32 wk old) which were wounded and inoculated were significantly shorter, more infected and developed more tip dieback (80%) than plants which were not wounded (32%). This indicates that damage caused by phytophagous insect species present on gorse through feeding and oviposition may enhance infection by F. tumidum. Wounding may release nutrients (e.g. Mg and Zn) essential for conidia germination and germ tube elongation and also provide easier access for germ tube penetration. Conidial germination and germ tube length were increased by 50 and 877%, respectively when incubated in 0.2% of gorse extract solution for 24 h compared with incubation in water. Inoculum suspensions amended with 0.2% of gorse extract caused more infection and significantly reduced biomass production of 24 wk old gorse plants than suspensions without gorse extract. A minimum number of about 900 viable conidia/infection site of F. tumidum were required to infect gorse leaves. However, incorporation of amendments (which can injure the leaf cuticle) or provision of nutrients (i.e. gorse extract or glucose) in the formulation might decrease the number of conidia required for lesion formation. Scanning electron micrographs showed that germ tube penetration of gorse tissue was limited to open stomata which partly explain the large number of conidia required for infection. The flowers and leaves were more susceptible to F. tumidum infection than the spines, stems and pods. An experiment to determine the number of infection sites required to cause plant mortality showed that the entire plant needs to be inoculated in order for the pathogen to kill 10 wk old plants as F. tumidum is a non systemic pathogen. The number of infection sites correlated strongly with disease severity (R² = 99.3%). At least 50% of the plant was required to be inoculated to cause a significant reduction in shoot dry weight. F. tumidum, applied as soil inoculant using inoculated wheat grains in three separate experiments, significantly suppressed gorse seedling emergence and biomass production. In experiments to determine the loading capacity of the insect species, E. postvittana, the largest insect species studied, carried significantly more (68) and deposited significantly more (29) F. tumidum conidia than the other species. Each E. postvittana, loaded with 5,000 conidia of F. tumidum, transmitted approximately 310 conidia onto gorse plants but this did not cause any infection or affect plant growth as determined by shoot fresh weight and shoot height. E. postvittana on its own did not cause any significant damage to gorse and did not enhance F. tumidum infection. It also failed to spread the pathogen from infected plants to the healthy ones. There was no evidence of synergism between the two agents and damage caused by the combination of both E. postvittana and F. tumidum was equivalent to that caused by F. tumidum alone. This study has shown that E. postvittana has the greatest capacity to vector F. tumidum since it naturally carried the largest and the most fungal spores (429 CFU/insect). Moreover, it naturally carried Fusarium spp. such as F. lateritium, F. tricinctum and Gibberella pulicaris (anamorph Fusarium sambucinum) and was capable of carrying and depositing most F. tumidum conidia on agar. Coupled with the availability of pheromone for attracting the male insects, E. postvittana may be a suitable insect vector for delivering F. tumidum conidia on gorse using this novel biocontrol strategy. Although it is a polyphagous insect, and may visit non-target plants, F. tumidum is a very specific pathogen of gorse, broom and a few closely related plant species. Hence, using this insect species to vector F. tumidum in a biological control programme, should not pose a significant threat to plants of economic importance. However, successful control of gorse using this "lure-load-infect" concept would depend, to a large extent on the virulence of the pathogen as insects, due to the large size of F. tumidum macroconidia, can carry only a small number of it.
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