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Field evaluation of fungal antagonists for the reduction of inoculum of Venturia inaequalis (Cke.) Wint.Ordon, Violetta. January 1998 (has links)
No description available.
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Reproductive and developmental biology of Aleochara bilineata Gyllenhal (Coleoptera:Staphylinidae)Gauvin, Marie-Josée. January 1998 (has links)
No description available.
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Potential of Smicronyx spp. (Coleoptera:Curculionidae) as biological control agents of Striga hermonthica (Del) Benth and Alectra vogelii Benth (Scrophulariaceae) in Burkina Faso (West Africa)Otoidobiga, Lenli Claude. January 1997 (has links)
No description available.
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Selection of effective antagonists against Rhizoctonia solani (AG-3), the causal agent of Rhizoctonia disease of potatoKabir, Nasreen Zahan. January 1996 (has links)
No description available.
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Seasonal occurrence and parasitism of lepidopterous pests of crucifers, and host age selection by a potential control agent: TrichogrammaGodin, Claude, 1970- January 1997 (has links)
No description available.
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The screening of potential fungal antagonists of pseudothecial formation by the apple scab pathogen : Venturia inaequalisPhilion, Vincent January 1994 (has links)
No description available.
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A study of fungal leaf decomposition in relation to biological control of the apple scab pathogen, Venturia inaequalisBernier, Julie January 1995 (has links)
No description available.
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A mathematical model for the control of Eldana saccharina Walker using the sterile insect techniquePotgieter, Linke 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Two mathematical models are formulated in this dissertation for the population growth of
an Eldana saccharina Walker infestation of sugarcane under the influence of partially sterile
released insects. The first model describes the population growth of and interaction between
normal and sterile E. saccharina moths in a temporally variable, but spatially homogeneous
environment. The model consists of a deterministic system of difference equations subject to
strictly positive initial data. The primary objective of this model is to determine suitable
parameters in terms of which the above population growth and interaction may be quantified
and according to which E. saccharina infestation levels and the associated sugarcane damage
may be measured.
The second model describes this growth and interaction under the influence of partially sterile
insects which are released in a temporally variable and spatially heterogeneous environment.
The model consists of a discretized reaction-diffusion system with variable diffusion coefficients,
subject to strictly positive initial data and zero-flux Neumann boundary conditions on a bounded
spatial domain. The primary objectives in this case are to establish a model which may be used
within an area-wide integrated pest management programme for E. saccharina in order to
investigate the efficiency of different sterile moth release strategies in various scenarios without
having to conduct formal field experiments, and to present guidelines by which release ratios,
frequencies and distributions may be estimated that are expected to lead to suppression of the
pest.
In addition to the mathematical models formulated, two practical applications of the models
are described. The first application is the development of a user-friendly simulation tool for
simulating E. saccharina infestation under the influence of sterile insect releases over differently
shaped spatial domains. This tool provides the reader with a deeper understanding as to what
is involved in applying mathematical models, such as the two described in this dissertation, to
real-life scenarios. In the second application, an optimal diversification of sugarcane habitats is
considered as an option for minimising average E. saccharina infestation levels, and as a further
consequence, improving the cost-efficiency of sterile insect releases. Although many special cases of the above model classes have been used to model the sterile
insect technique in the past, few of these models describe the technique for Lepidopteran species
with more than one life stage and where F1-sterility is relevant. In addition, none of these
models consider the technique when fully sterile females and partially sterile males are being
released. The models formulated in this dissertation are also the first to describe the technique
applied specifically to E. saccharina, and to consider the economic viability of applying the
technique to this species. Furthermore, very few examples exist of such models which go beyond
a theoretical description and analysis towards practical, real-life applications as illustrated in
this dissertation. / AFRIKAANSE OPSOMMING: Twee wiskundige modelle word in hierdie proefskrif vir die populasiegroei van ’n Eldana saccha-
rina Walker infestasie van suikerriet onder die invloed van gedeeltelik steriele, vrygelate insekte
daargestel. Die eerste model beskryf die populasiegroei van en -interaksie tussen normale en
steriele E. saccharina motte in ’n dinamiese, maar ruimtelik-homogene omgewing. Die model is
’n stelsel deterministiese verskilvergelykings onderhewig aan streng positiewe aanvangswaardes.
Die primˆere doelstelling met hierdie model is om geskikte parameters te bepaal in terme waarvan
die bogenoemde groei en interaksie gekwantifiseer kan word, en waarvolgens E. saccharina
infestasievlakke en die gepaardgaande suikerrietskade gemeet kan word.
Die tweede model beskryf hierdie groei en interaksie onder die invloed van gedeeltelik steriele
insekte wat in ’n dinamiese en ruimtelik-heterogene omgewing vrygelaat word. Die model
is ’n gediskretiseerde stelsel reaksie-diffusievergelykings met veranderlike diffusieko¨effisi¨ente
onderhewig aan streng positiewe aanvangswaardes en zero-vloei Neumann-randwaardes op ’n
begrensde ruimtelike gebied. Die primˆere doelstellings in hierdie geval is om ’n model tot stand
te bring wat in ’n area-wye, ge¨ıntegreerde pesbestrydingsprogram vir E. saccharina gebruik
kan word om die doeltreffendheid van verskillende steriele motvrylatingstrategie¨e te bepaal
sonder om daadwerklik veldeksperimente uit te voer, en om riglyne daar te stel waarvolgens
vrylatingsverhoudings, -frekwensies en -verspreidings bepaal kan word wat na verwagting na ’n
onderdrukking van die pes sal lei.
Bykomend tot die wiskundige modelle in hierdie proefskrif, word twee praktiese toepassings
van die modelle ook beskryf. In die eerste toepassing word ’n gebruikersvriendelike simulasie
hulpmiddel ontwikkel om E. saccharina infestasie onder die invloed van steriele insekvrylatings
in verskillende ruimtelike gebiede te simuleer. Hierdie toepassing fasiliteer ’n dieper begrip van
wat ter sprake is in die toepassing van wiskundige modelle, soos die twee modelle in hierdie
tesis, tot werklike scenario’s. In die tweede toepassing word ’n optimale diversifisering van
suikerriet habitats as ’n opsie vir die vermindering van die gemiddelde E. saccharina infestasie
vlakke beskou, en gevolglik word die verbetering van die koste-doeltreffendheid van steriele
insekvrylatings afgeskat. Alhoewel verskeie spesiale gevalle van die bogenoemde twee klasse van modelle reeds in die
verlede gebruik is om die doeltreffendheid van die steriele-insektegniek te modelleer, beskryf
weinig van hierdie modelle die tegniek vir Lepidopteriese spesies met meer as een lewensfase en
waar F1-steriliteit ter sprake is. Verder beskryf geen van hierdie modelle die tegniek waar algeheel
steriele wyfies en gedeeltelik steriele mannetjies vrygelaat word nie. Die modelle in hierdie
tesis is ook die eerste waar die tegniek spesifiek op E.saccharina toegepas word, en waar die
ekonomiese lewensvatbaarheid van die tegniek vir hierdie spesie oorweeg word. Verder bestaan
daar min voorbeelde van soortgelyke modelle wat verder gaan as ’n teoretiese beskrywing en
wiskundige ontleding na praktiese, werklike toepassings, soos in hierdie proefskrif ge¨ıllustreer.
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Epiphytic yeasts isolated from apple leaves to control of gray and blue mold fruit rots of appleFalconi, Cesar E. 14 June 1996 (has links)
Eight phylloplane yeasts were isolated from backyard apple trees in
Corvallis, OR. Yeast isolates were classified to genus or species level. All
isolates were tested in vitro for antagonistic activity against the postharvest
pathogens Botrytis cinerea and Penicillium expansum. Of these isolates,
Aureobasidium pullulans, Sporobolomyces roseus Rhodotorula sp., consistently
reduced mycelial growth of B. cinerea and P. expansum in nutrient yeast
dextrose agar (pH 4.5 or 7.0) incubated for 8 or 30 days at 24 or 1 C, respectively.
These three yeasts also were evaluated for their ability to suppress spore
germination of B. cinerea and P. expansum in a gradient of apple juice
concentrations and to suppress development of gray and blue mold lesions in
inoculated fruits of Golden Delicious apple. Germination of B. cinerea and P.
expansum was reduced significantly (P���0.05) when incubated with the yeast
isolates in 100 or 50% apple juice, but not in 0, 1 or 10% apple juice. S. roseus
and A. pullulans reduced significantly (P���0.05) the size of gray mold lesions in
wounded fruit stored at 5 C and 24 C by 63 to 72 and 81 to 90%, respectively,
when compared to the nontreated control. Size of blue mold lesions in fruit
stored at 5 and 24 C also were reduced significantly (P���0.05) by 66 to 38 and 74
to 63%, respectively, when pre-treated with S. roseus and A. pullulans. In
general, fruit rot suppression by some yeasts isolated in this study was similar in
magnitude to suppression obtained by Cryptococcus laurentii isolate 87-108, a
yeast with commercial potential to suppress postharvest rots of pome fruits.
Pretreatment of apple wounds with washed cells of A. pullulans, S. roseus,
Rhodotorula sp., resulted in disease suppression, but treatment of wounds with cell-free culture supernatant of these isolates did not affect lesion development. Population size of A. pullulans, S. roseus, and C. laurentii increased in apple wounds incubated at 5 or 24 C for up to 25 days, indicating that they colonized the wound site. Data collected in this study support the hypothesis that yeast isolates antagonize fruit pathogens by competing for nutrients in wounds on fruit surfaces. The isolates of A. pullulans and S. roseus show promise for commercial development. / Graduation date: 1997
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Biological control of gastrointestinal nematodes of small ruminants, using Bacillus thuringiensis (Berliner) and Clonostachys rosea (Schroers).Baloyi, Mahlatse Annabella. January 2011 (has links)
Gastrointestinal nematode parasites cause great losses in the production of small ruminants
through reduced productivity and the cost of preventive and curative treatments. Because of the
threat of anthelmintic resistance, biological control of sheep nematodes has been identified as an
alternative to anthelmintic drugs. Bacillus thuringiensis (Bt) (Berliner) and Clonostachys rosea
(Schroers) have been widely studied as biocontrol agents. B. thuringiensis has been used for the
biocontrol of insects and C. rosea has been successfully used as biocontrol agent of Botrytis
cinera (De Bary) in plants.
B. thuringiensis and C. rosea strains were isolated from soil collected from the Livestock Section
at Ukulinga Research Farm, University of KwaZulu Natal, Pietermaritzburg. Twenty-five strains
of Bt and 10 strains of C. rosea were successfully isolated. The Bt colonies were identified by
their circular, white, flat and undulate character, and the gram-positive and rod-shaped
endospores. C. rosea was identified by white colonies on Potato-dextose agar and the
characteristic conidiophores, which were branched and showed phialides at the tips.
In vitro screening of the isolates was undertaken to select the best isolates. The isolates that
caused significantly greater mortality were Bt isolate B2, B10 and B12 and C. rosea isolates P1,
P3 and P8. These isolates caused substantial nematode mortality in both faeces and water
bioassay. Nematode counts were reduced by 28.5% to 62% and 44% to 69.9% in faecal bioassay
for Bt and C. rosea, respectively. In the water bioassay, nematode counts were reduced by 62%
to 85% for Bt and by 62.7% to 89.3% for C. rosea.
The best inoculum level at which the best isolates were most effective, and the optimum
frequency of application were determined. The trial was conducted using bioassays with faeces
and water. Inoculum levels of 10(6), 10(8), 10(10), 10(12) spores ml-1 for Bt and 10(6), 10(8) and 10(10)
conidia ml-1 for C. rosea was used in the faecal bioassay. The inoculum levels tested in water
bioassay were 10(6), 10(8), 10(10) and 10(12) spores ml-1 for Bt and 10(9), 10(10), 10(11), 10(12) conidia ml-1 for
C. rosea. In the faecal bioassay, B2 was the most effective Bt isolate at an inoculum level of 10(10)
spores ml-1. Isolate P3 was the best C. rosea isolate at 10(8) conidia ml-1. In the water bioassay,
Isolate P3 caused a mortality of 85% at inoculum levels of 10(9), 10(10) and 10(11) conidia ml-1.
The performance of biological control agents in the field is sometimes inconsistent. Combining
different biocontrol agents may be a method of improving their reliability and performance.
However, the combination of most of the isolates was antagonistic, with efficacy less than that of
either individual biocontrol agent. In particular, Isolate P3 was more effective when used alone
than when combined with any other isolates. Therefore, the combination of biocontrol agents
does not always result in synergistic interaction. There were some additive interactions between
two bacterial isolates, and with one bacterial and fungal combination.
The effect of feeding the best of the biocontrol agents, or diatomaceous earth (DE), was
evaluated in sheep. Two doses of Bt (1g and 2g kg-1BW) and C. rosea (1g kg-1BW) reduced the
numbers of L3 nematode larvae in sheep faeces. The DE product (at 15% of feed) also
reduced L3 numbers but it was less effective than either the Bt or the C. rosea products.
Nematode counts were reduced by 74.6%, 75.1%, 84.6%, 68.5% and 27.5% for Bt 1g kg-1BW,
Bt 2g kg-1BW, C. rosea (1g kg-1 BW), DE and control, respectively. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.
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