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A study of Sclerotium rolfsii, sacc.Jefferson, R. N. January 1936 (has links)
Sclerotium rolfaii Secc. is a fungus that is prevalent throughout the southern states, and at times causes very serious losses to farm crops and ornamental plants. It causes a disease known as Sclerotium Wilt, Southern Wilt, or Southern Blight.
The Virginia Agricultural Experiment Station has received many complaints of Sclerotium Wilt on ornamental plants in the last few years, but has been unable to give any definite recommendations because no satisfactory method of control has been developed. the object of this investigation was to study the characteristics of the fungus and to discover, if possible, some method or methods of checking the disease when established. / Master of Science
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Characterization and control of Phaeomoniella chlamydospora in grapevinesGroenewald, Michelle 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Petri grapevme decline, also known as black goo, slow die-back and
Phaeoacremonium grapevine decline, causes significant losses of young vines worldwide.
Species of Phaeoacremonium, Phaeomoniella chlamydospora and related
genera are associated with this grapevine disease. This study investigates the
Phaeoacremonium-complex and Phaeomoniella chlamydospora, focussing on the
species isolated from grapevines. Fungicide sensitivity of Pa. chlamydospora and the
possibility of employing molecular techniques for the detection of Pa. chlamydospora
in grapevines were also investigated.
In an overview of the literature on Petri grapevine decline the disease history
and the relatedness of Petri grapevine decline to esca is discussed. Petri grapvine
decline occurs in propagation material or young vines. Infected material can appear
asymptomatic and therefore the possibilities of molecular techniques for identification
were also investigated in the literature.
In South Africa Pa. chlamydospora is the dominant organism causing Petri
grapevine decline and therefore different fungicides were evaluated to control this
fungus. Six isolates of Pa. chlamydospora, from Stellenbosch, Wellington, Somerset
West and Malmesbury of Western Cape province, South Africa, were screened
against twelve fungicides testing their effect on mycelial inhibition in vitro. These
fungicides included benomyl, chlorothalonil, fenarimol, fosetyl-Al, iprodione,
kresoxim-methyl, mancozeb, metalaxyl, prochloraz manganese chloride, quintozene,
tebuconazole and thiram. Results provided the base-line sensitivity of South African
isolates of Pa. chlamydospora. Benomyl, fenarimol, kresoxim-methyl, prochloraz
manganese chloride and tebuconazole were the most effective (with EC50 values
ranging from 0.01 to 0.05 ug/ml) for inhibiting mycelial growth of Pa.
chlamydospora in vitro. This in vitro test gave a good indication of which fungicides
could be selected for further studies in glasshouses and nurseries.
The molecular phylogeny of Phaeoacremonium and Phaeomoniella isolates
from grapevines of South Africa, or isolates obtained from the Centraalbureau voor
Schimmelcultures (CBS) in the Netherland, were investigated. Sequence data were
created from the rONA region and partial B-tubulin gene of 33 of these isolates using
the PCR technique. This sequence data were analysed with PAUP* version 4.Ob2a.
An analysis of the sequence data confirmed the genus Phaeomoniella to be distinct from Phaeoacremonium (Pm.) based on DNA phylogeny. Although morphologically
similar, the species status of Pm. aleophi/um and Pm. angustius was confirmed with
DNA phylogeny and cultural characteristics. Pm. aleophilum has an optimum growth
rate at 30°C and the ability to grow at 35°C, where as Pm. angustius has an optimum
growth rate at 25°C and cannot grow at 35°C_ Pm. viticola was shown to be
synonymous with Pm. angustius, and a new species, Pm. mortoniae, was newly
described from grapevine occurring in California. Futhermore, Pm. aleophilum was
newly reported from South Africa and grapevine isolates thought to be Pm. inflatipes
were all re-identified as Pm. aleophilum. These findings therefore also shed some
doubt on the possible role of Pm. inflatipes in Petri grapevine decline. It was
confirmed that Pa. chlamydospora, Pm. aleophilum and Pm. angustius are the species
involved in Petri grapevine decline. Pm. mortoniae was isolated from grapevines, but
its pathogenicity should still be confirmed and the role of Pm. injlatipes in Petri
grapevine decline remains unclear.
Pa. chlamydospora has been routinely isolated from symptomless propagation
and nursery material. Because the disease can take years to develop, it is crucial that
healthy propagation material is used at planting. Pa. chlamydospora is a slowgrowing
fungus, and positive identification from symptomless grapevine tissue can
take up to 4 wks. The possibility of employing molecular techniques for the detection
of Pa. chlamydospora in apparently healthy grapevines was investigated. Speciesspecific
primers (PCLI and PCL2) based on the regions ITSI and ITS2 were designed
for Pa. chlamydospora. These primers were highly sensitive and amplification was
achieved from genomic DNA of Pa. chlamydospora from as low as 16 pg.
Phaeoacremonium spp., related genera and common fungal taxa from grapevines
were tested with these primers, but positive amplification was achieved for Pa.
chlamydospora only. The presence of Pa. chlamydospora in symptomless grapevine
tissue culture plants was confirmed by PCR within 24 hours. These primers therefore
allow rapid and accurate identification of Pa. c~lamydospora. Testing on a larger
scale with nursery material should be conducted to determine the feasibility of using
these species-specific primers in the grapevine industry. / AFRIKAANSE OPSOMMING: Petri-terugsterwing van jong wingerde, ook algemeen bekend as "black goo" en
Phaeoacremonium-terugsterwing, veroorsaak wêreldwyd groot geldelike verliese in
die wingerdbedryf. Spesies van Phaeoacremonium, Phaeomoniella chlamydospora
en verwante genera word met hierdie wingerdsiekte geassosieer. In die tesis word In
oorsig gegee van die geskiedenis van hierdie siekte, die verwantskap tussen Petriterugsterwing
en esca, en moontlike maniere van siektebestuur. Swamme wat by die
siektekompleks betrokke is, kan in simptoomlose plantweefsel voorkom en daarom is
die moontlikhede van die gebruik van molekulêre tegnieke vir swamidentifikasie in
oënskou geneem.
In Suid-Afrika is Pa. chlamydospora die dominante swam wat met Petriterugsterwing
geassosieerword, gevolglik is verskillende fungisiedes vir die chemiese
beheer van Pa. chlamydospora geëvalueer. Ses isolate van Pa. chlamydospora,
versamel vanaf verskillende areas in die Wes-Kaap provinsie, is in dié studie gebruik.
Benomyl, chlorothalonil, fenarimol, fosetyl-Al, iprodione, kresoxim-methyl,
mancozeb, metalaxyl, prochloraz manganese chloride, quintozene, tebuconazole en
thiram se effek op miselium inhibisie van Pa. chlamydospora is in vitro geëvalueer.
Benomyl, fenarimol, kresoxim-methyl, prochloraz manganese chloride en
tebuconazole was die mees effektiewe middels. Die effektiewe konsentrasie waarby
50% van die miselium groei geïnhibeer is (EKso),was tussen 0.01 en 0.05 ug/ml vir
die mees effektiewe groep middels. Benomyl, fenarimol, kresoxim-methyl,
prochloraz manganese chloride en tebuconazole het in vitro goeie potensiaal getoon,
en verder toetse moet in vivo uitgevoer word.
'n Molekulêre studie is van Phaeoacremonium en Phaeomoniella isolate;
verkry uit Suid-Afrikaanse wingerde, of vanaf die "Centraalbureau voor
Schimmelcultures" (CBS) van Nederland; gedoen. Deur van die PKR tegniek
gebruik te maak, is die basispaaropeenvolgingsdata van 33 isolate, van die ITSl, 5.8S,
ITS2 rDNA area en die gedeeltelike B-tubullen geen verkry. Gekombineerde
molekulêre data het die teorie ondersteun dat Phaeomoniella (Herpotrichiellaceae)
gedistansieerd is van Phaeoacremonium (Magnaporthaceae). Pm. aleophilum en Pm.
angustius was morfologies moeilik onderskeibaar, maar kon op grond van molekulêre
data en kulturele eienskappe onderskei word. Pm. aleophilum se optimum
groeitemperatuur was by 30°C en die swam besit die vermoë om by 35°C te groei. Pm. angus/ius se optimum groeitemperatuur was by 25°C, maar het nie by 35°C
gegroei nie. 'n Studie van molekulêre en kulturele eienskappe het getoon dat Pm.
angus/ius en Pm. viticola sinoniem is. 'n Nuwe spesie, Pm. mortoniae, wat uit
wingerde van Kalifornie geïsoleer is, is beskrywe. Verder is Pm. aleophilum die
eerste keer in Suid-Afrikaanse wingerde aangetref en Pm. tnflatipes isolate, wat
vanuit wingerde geïsoleer is, is almal met molekulêre data gewys om Pm. aleophilum
te wees. Hierdie bevindinge trek die rol van Pm. inflatipes in Petri-terugsterwing van
wingerde in twyfel.
Phaeomoniella chlamydospora IS m voortplantingsmateriaal en
kwekerystokkies opgespoor. Omdat dit jare kan duur voordat siektesimptome
ontwikkel, is dit belangrik om vroegtydig te weet of jong stokkies met Pa.
chlamydospora geïnfekteer is. Pa. chlamydospora groei baie stadig en positiewe
identifikasie van simptoomlose infeksies duur tot vier weke. Die toepassing van
molekulêre tegnieke vir die vinnige identifikasie van Pa. chlamydospora in wingerde
is dus ondersoek. Spesie-spesifieke oligonukleotiedes (PCU en PCL2) is vir Pa.
chlamydospora ontwerp. Hierdie oligonukleotiedes is uiters sensitief en genomiese
DNA van Pa. chlamydospora is van so laag as 16 pg geamplifiseer.
Phaeoacremonium spp., verwante genera en algemene swamme vanuit
wingerdmateriaal is met die oligonukleotiedes getoets, maar positiewe amplifikasie
was slegs met Pa. chlamydospora moontlik. Die teenwoordigheid van Pa.
chlamydospora is binne 24 uur in asimptomatiese wingerd weefselkultuurplantjies
bevestig. Hierdie oligonukleotiedes identifiseer Pa. chlamydospora vinnig en
akkuraat en toetsing op 'n groter skaal moet vervolgens met kwekerymateriaal
onderneem word.
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Infection pathways of Botrytis cinerea on selected wine grape cultivarsDu Preez, Izak Frederik 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch / ENGLISH ABSTRACT: An understanding of the infection pathways of Botrytis cinerea in grape bunches will help
to combat this devastating pathogen of grape. Many studies have been done to determine the
possible infection pathways of B. cinerea. Most of these studies made use of artificial
inoculations that deposit groups of conidia on the plant surface. The deposition of clusters of
conidia is not a common phenomenon in nature. The aim of this study was to investigate the
infection pathways of (i) naturally- as well as (ii) artificially inoculated B. cinerea conidia
during all the phenological stages of three wine grape cultivars, and to compare the (iii)
pathogenicity and virulence, on grape and nectarine fruit, of isolates obtained from different
host plants.
In the natural infection study the occurrence of Botrytis cinerea and subsequent disease
expression at different positions in bunches of wine grapes (cultivars Chenin Blanc, Shiraz
and Chardonnay) was determined from 1999 to 2001. Different techniques were used to
detect viable inoculum at different positions (rachises, laterals, pedicels, and the peicel end,
cheek and style end of berries) in bunches. Isolations were made on Kerssies' B. cinerea
selective medium, or bunches were used untreated, or treated with paraquat. Paraquat was
used to terminate host resistance and to promote the development of the pathogen from the
tissues. The material was used untreated to detect the pathogen on the surface, or were
surface-sterilized to detect mycelia (latent infection) in the tissue. In the artificial inoculation
study, bunches of wine grapes (cultivars Chenin Blanc, Chardonnay and Shiraz) at pea size,
bunch closure, and harvest were dusted with dry conidia of Botrytis cinerea in a settling
tower and incubated for 24 h at high relative humidity (±93%). Following incubation, the
bunches were divided in two groups. The one group was surface-sterilised in 70% ethanol
for 5 s, the other group was left untreated. Bunches of the sterile group, and from the
untreated group were used for isolation. From each bunch rachis segments, laterals, pedicels
and berry skin segments (from the pedicel-end and cheek) were removed. The sections were
placed in Petri dishes on Kerssies' B. cinerea selective medium and on a water agar medium supplemented with paraquat, and incubated at 22°C under diurnal light. Occupation by the
pathogen was positively identified by the formation of sporulating colonies of B. cinerea on
the different tissues. Lastly, in the virulence and pathogenicity experiment on grape and
nectarine fruit Botrytis cinerea isolates, which were obtained from different host plants, were
compared by simulating natural infection. Cold-stored fruit, considered highly susceptible to
B. cinerea were therefore inoculated with single, airborne conidia of the pathogen. Different
tests were conducted to assess surface penetration and lesion formation. Isolations were
made from fruit skins on Kerssies' B. cinerea selective medium. Nectarine fruit were treated
with paraquat, and grape berries were frozen for 1 h at -12°C. Paraquat and freezing were
used to terminate host resistance and to promote the development of the pathogen from the
tissues.
In the natural infection studies B. cinerea occurred in a consistent pattern in bunches of the
three cultivars. B. cinerea consistently developed from the tissue of the rachis, laterals,
pedicel and pedicel-end, but not from the berry cheek. The rachis, lateral and pedicel
contained much higher levels of B. cinerea than any position on the berry. Furthermore, the
pathogen consistenly occurred at relatively high levels on the rachises throughout the season.
Collectively, the data showed that in the Western Cape province, B. cinerea occured more
regularly in wine grape bunches during the early part of the season, than later in the season.
The data of the artificial studies confirmed the findings made with the natural infection
studies. In these experiments the pathogen resided more often on the structural bunch parts
than on the berries. Overall, the isolation studies revealed that conidia occurred
predominantly on the rachis. The incidence of B. cinerea was furthermore constantly high in
the inner bunch after each inoculation, and in bunches of different maturities. The data
therefore indicated that, when available, conidia penetrated loose and tight clustered bunches
in a similar way. Finally, in the virulence and pathogenicity experiments the results showed
clearly that no host specialisation exists in the B. cinerea isolates used in this study.
From these studies it is clear that in the Western Cape province B. cinerea occurs more
readily in the inner structural parts of the bunches and more so during the earlier parts of the
season. These findings should be considered when planning and implementing disease
control programmes. / AFRIKAANSE OPSOMMING: INFEKSIEWEË VAN BOTRYTIS CINEREA OP GESELEKTEERDE WYNDRUIF
KULTIVARS
Indiepte kennis van die infeksieweë van Botrytis cinerea op druiwetrosse word benodig
vir die beheer van dié vernietigende patogeen van druiwe. Vele studies is al gedoen om die
moontlike infeksieweë van die swam op druiwe trosse te ondersoek. Die meeste van die
studies het gebruik gemaak van kunsmatige inokulasie tegnieke waar die konidia van die
swam in groepe op die korreloppervlak gedeponeer is. In die natuur is dit 'n rare verskynsel
dat konidia in groepe op die korreloppervlak land. Die doel van die studie was om die
infeksieweë van B. cinerea op drie wyndruif kultivars te ondersoek wat (i) natuurlik- en (ii)
kunsmatig geïnokuleer is met konidia gedurende al die fenologiese stadia, en om die (iii)
virulensie en patogenisisteit van isolate wat van verskillende gashere verkry is, op druiwe en
nektariens te vergelyk.
In die natuurlik-geïnokuleerde druiwe is die voorkoms van B. cinerea en die gevolglike
siektevoorkoms op verkillende posisies in trosse van wyndruiwe (Chenin Blanc, Chardonnay,
Shiraz) gedurende 1999 tot 2001 bepaal. Verskillende tegnieke is gebruik om lewensvatbare
inokulum by verskillende posisies (ragis, lateraal, pedisel en pedisel-end van die korrel) in
die tros waar te neem. Isolasies is op Kerssies' B. cinerea selektiewe medium gemaak, of
trosse is onbehandeld gebruik, of behandel met paraquat. Paraquat is gebruik om die gasheer
se natuurlike weerstand te verlaag en om die ontwikkeling van die patogeen te bevorder. Die
plantmateriaal is onbehandeld gelaat om die patogeen op die oppervlak waar te neem, of die
oppervlak is gesteriliseer om die latente myselium in die weefsel waar te neem. In die
kunsmatige inokulasiestudies is trosse, van wyndruiwe (Chenin Blanc, Chardonnay, Shiraz),
geïnokuleer met droë spore, van B. cinerea, in 'n inokulasietoring en die plantmateriaal is dan
geinkubeer vir 24 h by 'n hoë relatiewe humiditeit (93%). Na die inkubasie proses is die
trosse in twee groepe verdeel. Die een groep druiwe het oppervlak sterilisasie ondergaan in
70% etanol vir 5 s, en die ander groep was onbehandeld gelaat. Trosse van die onbehandelde
en gesteriliseerde groep druiwe is gebruik vir isolasies. Vanuit elke tros is daar segmente van
die ragis, laterale, pediselle en korrels (van die pedisel-end en wang gedeeltes) geïsoleer. Die segmente is in Petri bakkies met Kerssies' B. cinerea selektiewe medium en op water agar
medium, wat paraquat bevat het, geïsoleer en geïnkubeer onder 'n 12 h dagligperiode teen
22°C. Die patogeen is positief geïdentifiseer deur sporuierende kolonies op die onderskeie
weefseltipes. Laastens, in die virulensie- en patogenisiteitsproewe op druiwe en nektariens is
verskillende isolate van B. cinerea, verkry vanaf verskillende gasheerplante, vergelyk deur
natuurlike inokulasie toestande na te boots. Koue opgebergde vrugte, wat beskou word as
hoogs vatbaar vir die infeksie van B. cinerea, is geïnokuleer met droë, enkel luggedraagde
spore van die patogeen. Verskillende toetse is gedoen om die oppervlak penetrerende en
letselvormende vermoëns van die onderskeie isolate te toets. Isolasies is van die skille van
die vrugte gemaak en op Kerssies' B. cinerea selektiewe medium geplaas. Die
nektarienvrugte is met paraquat behandel en die druifkorrels is gevries vir 1 h teen -12°C.
Paraquat en bevriesing is gebruik om die gasheer se weerstand te verlaag en om die
ontwikkeling van die patogeen te bevorder.
In die natuurlik-geïnokuleerde studies het B. cinerea 'n konstante patroon getoon in die
trosse van die drie verskillende wyndruif kultivars. B. cinerea het konstant ontwikkel uit die
ragis, laterale, pedisel en pedisel-end, maar selde uit die korrelwang. Die ragis, lateral en
pedisel dele het baie hoër vlakke van van die swam bevat as enige deel op die korrel. Die
patogeen het ook konstant volop deur die hele seisoen op die ragis voorgekom. Gesamentlik
wys die data dat, B. cinerea in wyndruiwe, in die Wes Kaap provinsie, meer geredelik vroeër
in die seisoen voorkom, eerder as later.
Data van die kunsmatige inokulasiestudies het die bevindinge van die natuurlike
inokulasiestudies tot 'n groot mate bevestig. In dié studies het die patogeen meer geredelik
die strukturele dele van die tros, eerder as op die korrels, bewoon. Oor die algemeen het die
isolasieproewe gewys dat die konidia meer op die ragis voorkom as op enige ander deel. Die
voorkoms van B. cinerea was ook oor die algemeen baie hoër in die strukturele dele van die
tros, as op die korrel self. Die verskynsel het onder trosse van verskillende
ontwikkelingsvlakke voorgekom. Die data het dus ook gewys dat konidia, wanner dit
beskikbaar is, minder- sowel as meer kompakte trosse op 'n soortgelyke manier penetreer.
Laastens, in die virulensie en patogenisiteitseksperimente het die resultate duidelik gewys dat
daar geen gasheer spesifieke gedrag onder B. cinerea isolate is nie.
In die studies het dit duidelik na vore gekom dat, B. cinerea meer geredelik in die
strukturele binne dele van die wyndruif tros, in die Wes Kaap provinsie voorkom. En so ook eerder aan die begin van die seisoen, as later in die seisoen. Dié kennis moet in aanmerking
geneem word by die beplanning en implementering van siektebeheerprogramme.
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Synergistic effects of mixtures of the kresoxim-methyl fungicide and medicinal plants extracts in vitro and in vivo against Botrytis Cinerea.Knowles, Cindy-Lee January 2005 (has links)
The fungus Botrytis cinerea is an opportunistic pathogen on a wide variety of crops, causing disease known as grey mould through infections via wounds or dead plant parts. Synthetic fungicides for controlling this disease are fast becoming ineffective due to the development of resistance. This, coupled with consumers world wide becomng increasingly conscious of potential environment and health problems associated with the build up of toxic chemicals, (particularly in food products), have resulted in pressure to reduce the use of chemical pesticide volumes as well as its residues. An emerging alternative to random synthesis is the study and exploitation of naturally occurring products with fungicidal properties. There have been reports on the uses of synthetic fungicides for the control of plant pathogenic fungi. When utilized in two-way mixtures, such fungicides may maintain or enhance the level of control of a pathogen at reduced rates for both components utilized in combinations, or alone at normal rates. For this study it was hypothesize that the addition of plant extracts may enhance the antifungal efficacy of the synthetic strobilurin fungicide, kresoxim-methyl against Botrytis cinerea.
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Tree resistance and responsiveness to mechanical damage and fungal pathogens in dipterocarp forest of Sabah, MalaysiaMohd Salim @ Halim, Jamilah January 2009 (has links)
A survey of dipterocarp forest in four sites revealed that the incidence of stem canker was relatively low but high localized incidences were recorded. No consistent association was obtained between the presence of mechanical damage and cankers. Cankers occurred more frequently on dipterocarps and less frequently on euphorbs. Field studies and experimental manipulations were used to compare sapling resistance and responsiveness to wounding and stem breakage in relatively nutrient-rich, alluvial forest and relatively nutrient-poor, sandstone ridge forest. Species found on sandstone ridges showed greater resistance to damage (e.g., greater stem flexibility, narrower crowns) than those on alluvial soils. Species common on alluvial soils tended to be more responsive to damage (e.g., faster wound closure rates, more likely to re-sprout). Results from manipulation experiments conducted on pot-grown seedlings were consistent with results from the field studies, where conditions of greater nutrient availability, saplings closed wounds at faster rates, had less flexible stems, more narrow crowns, and lower levels of foliar total phenolics. Species showed differential rezones to resource availability which, in part, may relate to contrasting strategies for investment in passive defence (i.e., resins and phenolics) over investment in growth. Through their narrower crowns, greater whole stem flexibility, and lesser stem taper, tree species characteristic of sandstone ridges had greater resistance to mechanical damage from debris falling from above than congeneric species characteristic of alluvial soils. Tree species characteristic of alluvial soils were more responsive to damage than congeners on sandstone ridges, by producing earlier and longer sprouts following stem snapping and more rapid rates of wound closure following wounding.
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Structure of root associated and soil fungal and bacterial communities in Southeast Asia tropical forestMustafa Bakray, Nur Aqilah Binti January 2018 (has links)
The tropical rainforest has interested ecologists for hundreds of years because of its vast species diversity. The distribution and establishment of trees is related to soil properties and rootassociated microorganisms. The coexistence of hyper-diverse plant communities in tropical rainforests has resulted in associations being formed with belowground communities, mycorrhizas (particularly arbuscular mycorrhizal (AM), ectomycorrhizas (ECM)) and root associated bacterial communities. The rapid deforestation in Southeast Asia is causing the loss of the dominant and important tree species belonging to the family Dipterocarpaceae. It is important to understand whether different host species in the same environment maintain mycorrhizal and bacterial diversity, especially mycorrhizas with a restricted host range. In this study, I examine the ecology of mycorrhizas and bacteria associated with Dipterocarpaceae and also the plant community as a whole. The aim of this project is to understand the effect of host properties (e.g. species, size), soil factors (e.g. nutrient concentrations) and spatial factors on mycorrhizal fungi and bacterial diversity and community structure. The research took place in two Centre for Tropical Forest Science (CTFS) plots in Malaysia: Pasoh Forest Reserve (in Negeri Sembilan) and Danum Valley Conservation Area (in Sabah). Molecular protocols and a modern technique, Next Generation Sequencing (NGS), were adopted to quantify mycorrhizal and bacterial loads in tropical plants. ITS1 and ITS2 regions were used for ECM, 18S rRNA were used for AM, and 16S rRNA were used for bacteria. Mycorrhizas and bacteria present in the roots of Dipterocarpaceae from 60 individual plants belonged to 25 species within 6 genera were traced and sampled in 2015. To my knowledge, this study is the first attempt to study root-associated bacteria across multiple species within a single family, Dipterocarpaceae. Dipterocarpaceae's species was found to significantly influence root bacteria. Analyses showed that mycorrhizal communities are similar on the host, unlike the null model. Dipterocarpaceae was previously believed to solely host ECM, but this study disproves this. This study shows that Dipterocarpaceae can have dual colonization, as it iv can also associate with AM fungi. One soil core of 10 cm × 10 cm × 7.5 cm were collect randomly in three subplot and further divided at 2.5 cm each slice into 75 individual 'microcubes' of 2 cm × 2 cm × 2.5 cm depths enumerates a total of 192 fine root samples. Multivariate analysis revealed that AM fungi tend to associate with non-dipterocarp (as well as unidentified families) while ECM fungi tend to associate with dipterocarps. Data was also collected on host attributes, plant size, and root density. Dipterocarpaceae size does not influence the distribution of mycorrhizal or bacterial communities. The root density reduces as depth increases. Therefore, root density does have a significant influence on mycorrhizal community structure. The diversity of ECM and AM fungal communities within cubes decreased significantly with depth (p < 0.001), whereas the mycorrhizal communities did not change across horizontal distances within cubes. To investigate whether there is a relationship between belowground communities and soil properties, soil macro and micro nutrients were examined and a multivariate analysis was performed. The results showed that communities of belowground (mycorrhizal and bacterial) species correlate with soil parameters. Spatial scale also had an effect on community assembly, independent of environmental variation. These results demonstrate that mycorrhizal fungal communities can vary substantially over very fine spatial scales, and that the distribution of roots from different species do not reflect their proximity aboveground. This study clearly demonstrates the widespread presence of mycorrhizal fungi and root associated bacteria in tropical rainforest plants.
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Phytophthora crown rot of almond and cherry trees : pathogens, rootstock and scion susceptib[i]lity and controlWicks, T. J. (Trevor J.) January 1987 (has links) (PDF)
Bibliography: leaves 169-185.
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Phomopsis taxon 1 on grapevine : pathogenicity and management / Belinda Rawnsley.Rawnsley, Belinda January 2002 (has links)
" August 2002." / Bibliography: leaves 218-235. / viii, 235 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The pathogenicity of Phomopsis taxon 1 is examined in relation to symptom expression and bud loss on grapevines. Phomopsis taxon 1-specific DNA probe, pT1P180, and taxon 2-specific probe, pT1P25, were used to detect Phomopsis taxon 1 and Phomopsis taxon 2 in infected buds, canes and shoots in glasshouse and field experiments. Experiments confirm the isolates of taxon 1 examined did not cause leaf or shoot symptoms associated with Phomopsis cane and leaf spot, and that taxon 2 is more virulent than taxon 1. Suggests that taxon 1 (Diaporthe) is an endophyte which does not cause harm to the grapevine and that chemical control is not warranted for control of taxon 1 on grapevine. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2002
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Crystallographic studies of Pyrenophora tritici-repentis ToxASarma, Ganapathy N. 04 October 2005 (has links)
Tan spot of wheat is an economically significant disease caused by the fungal
pathogen, Pyrenophora tritici-repentis. Certain races of the fungus secrete Ptr ToxA
(ToxA), a 13.2 kDa proteinaceous host-selective toxin that is responsible and
sufficient to cause disease in susceptible wheat varieties. Disease symptoms develop
only when the ToxA gene in the fungus and a single gene in the wheat host are
expressed. The understanding of this gene-for-gene interaction could be instrumental
towards control of the disease and is also being developed as a model system for
understanding host-pathogen interactions. Here, this effort is given a solid structural
foundation through crystallographic analysis of the ToxA structure.
The ToxA structure was solved at 1.65 Å resolution using the anomalous
signal from inherently present sulfur atoms. The monomeric toxin adopts a β-sandwich
fold of two anti-parallel β-sheets composed of four strands each. The
mapping of existing mutation data onto the structure reveals that a sequence of Arg-
Gly-Asp(RGD) and surrounding residues required for activity are present on a
solvent-exposed loop thereby making them potential candidates for recognition events
that are required for ToxA activity. Unexpectedly, after a simple circular permutation,
the ToxA structure is topologically identical to the classic mammalian RGD containing
fibronectin type III (FnIII) domain, and furthermore the RGD residues are
topologically equivalent. These results support the hypothesis that ToxA, like FnIII,
interacts with an integrin-like receptor on the host plant cell surface.
There has been a renewed interest in the method of using the anomalous signal
from sulfur atoms to solve protein structures. As a spin-off of the structure solution
work, the data were systematically analyzed to study the effects of crystal decay,
resolution and data redundancy on the ability to locate the sulfur positions and
subsequent phasing of the protein. The analyses show that the choices made about data
redundancy and resolution limits may be crucial for the structure determination and
that anomalous correlation coefficients are helpful indicators in making these choices. / Graduation date: 2006
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Biology, pathogenicity and diversity of Fusarium oxysporum f.sp. cubenseGroenewald, Susan. January 2005 (has links)
Thesis (M.Sc.)(Microbiology)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.
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