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Host-parasite relationships in Verticillium wilt of tobacco.Wright, Donald Stranack Cottle. January 1972 (has links)
No description available.
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The effects of Trichoderma (Eco-T) on biotic and abiotic interactions in hydroponic systems.Neumann, Brendon John. January 2003 (has links)
The following body of research provides a detailed overview of the interactive effects of
biocontrol agents and environmental factors and how these influence both the host plant
and pathogen populations within hydroponic systems.
Pythium and other zoosporic fungi are pathogens well suited to the aquatic environment
of hydroponics. Motile zoospores facilitate rapid dispersal through fertigation water,
resulting in Pythium becoming a yield reducing factor in most hydroponic systems and
on most crops. With increasing trends away from pesticide use, biocontrol is becoming
an ever more popular option. Unfortunately, much of our knowledge of biocontrol agents
and their formulation can not be directly transferred to the widely differing environments
of hydroponic systems. Paulitz (1997) was of the opinion that if biocontrol was to be
successful anywhere, it would be in hydroponics. This is primarily due to the increased
ability, in hydroponics, to control the growing environment and to differentiate between
the requirements of the pathogen versus those of the host plant and biocontrol agent.
Key environmental factors were identified as soil moisture, root zone temperature, form
of nitrogen and pH.
A review of the literature collated background information on the effects of biocontrol
agents and environmental manipulation on plant growth and disease severity in
hydroponic systems.
A commercial formulation of Trichoderma (Eco-T(R1)) was used as the biocontrol agent
in all trials. Dose responses in Pythium control and plant growth stimulation in lettuce
were first determined using a horizontal trough system (closed system). In such systems
optimum application rates were found to be lower than in field application (1.25x10[to the power of 5]
spores/ml). This is probably because Trichoderma conidia are not lost from the system,
but re-circulate until being transported into the root zone of a host plant. No significant
growth stimulation was observed, although at high doses (5x10[to the power of 5] and 2.5x10[to the power of 5] spores/ml)
a significant reduction in yield was recorded. Possible reasons for this growth inhibition
are suggested and a new theory is proposed and investigated later in the thesis. In an
open system of cucumber production (drip irrigated bag culture) no statistically
significant results were initially obtained, however, general trends still showed the
occurrence of positive biocontrol activity. The initial lack of significant results was mostly
due to a poor knowledge of the horticulture of the crop and a lack of understanding of
the epidemiology behind Trichoderma biocontrol activity. These pitfalls are highlighted
and, in a repeat trial, were overcome. As a result it could be concluded that application
rates in such systems are similar to those used in field applications.
Management of soil moisture within artificial growing media can aid in the control of
Pythium induced reductions in yield. A vertical hydroponic system was used to
determine the interactive effects of soil moisture and Trichoderma. This system was
used because it allowed for separate irrigation regimes at all 36 stations, controlled by
a programmable logic controller (PLC). With lettuce plants receiving optimum irrigation
levels, no significant reduction in yield was observed when inoculated with Pythium.
However, after Pythium inoculation, stresses related to over- or under-watering caused
significant yield losses. In both cases, Trichoderma overcame these negative effects
and achieved significant levels of disease control, especially under higher soil moisture
levels. Growth stimulation responses were also seen to increase with increasing soil
moisture. Similar results were obtained from strawberry trials. These results show that
Pythium control is best achieved through the integration of Trichoderma at optimum soil
moisture. However, where soil moisture is above or below optimum, Trichoderma serves
to minimize the negative effects of Pythium, providing a buffering capacity against the
effects of poor soil moisture management.
Pythium, root zone temperature and form of nitrogen interact significantly. In
greenhouse trials using horizontal mini troughs with facilities for heating or cooling
recirculating water, nitrate fertilizer treatments resulted in statistically significant results.
Lettuce growth was highest at 12°C, although no significant differences in yield were
observed between 12-24°C. Pythium was effective in causing disease over the same
temperature range. Pythium inoculation did not result in yield reduction at 6 and 30°C.
Trichoderma showed a slight competitive advantage under cooler temperatures (i.e., 12 degrees C), although significant biocontrol occurred over the 12-24 degrees C range. Ammonium
fertilizer trials did not generate statistically significant data. This is possibly due to
complex interactions between root temperature, ammonium uptake, and competitive
exclusion of nitrification bacteria by Trichoderma. These interactions are difficult to
replicate over time and are probably influenced by air temperature and available light
which are difficult to keep constant over time in the system used. However, the data did
lead to the first clues regarding the effects of Trichoderma on nitrogen cycling as plants
grown with a high level of ammonium at high temperatures were seen to suffer more
from ammonium toxicity when high levels of Trichoderma were added.
In further trials, conducted in the recirculating horizontal mini trough system, it was
determined that Trichoderma applications resulted in an increase in the percentage
ammonium nitrogen in both the re-circulating solution and the growing medium. This
was a dose-related response, with the percentage ammonium nitrogen increasing with
increasing levels of Trichoderma application. At the same time an increase in
ammonium in the root tissue was observed, corresponding with a decrease in leaf
nitrate levels and an increase in levels of Cu, Na, Fe and P in leaf tissue. In independent
pot trials, populations of nitrifying bacteria in the rhizosphere were also seen to
decrease with increasing Trichoderma application rates. This led to the conclusion that
the increase in ammonium concentration was as a result of decreased nitrification
activity due to the competitive exclusion of nitrifying bacteria by Trichoderma. The
possibility that Trichoderma functions as a mycorrhizal fungus and so increases the
availability of ammonium for plant uptake is not discarded and it is thought that both
mechanisms probably contribute.
Water pH provides the most powerful tool for enhancing biocontrol of Pythium by
Trichoderma. Trichoderma shows a preference for more acidic pHs while Pythium
prefers pHs between 6.0 and 7.0. In vitro tests showed that Trichoderma achieved
greater control of Pythium at pH 5.0, while achieving no control at pH 8.0. In greenhouse
trials with the recirculating horizontal mini trough system, yield losses resulting from
Pythium inoculation were greatest at pH 6.0 and 7.0, with no significant reduction in
yield at pH 4.0. Biocontrol activity showed an inverse response with greatest biocontrol
at pH 5.0. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2003.
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Comparative studies on genetic variability and fungicide resistance in Tapesia yallundaeNtushelo, Khayalethu 12 1900 (has links)
Thesis (MScAgric)--Stellenbosch University, 1998. / ENGLISH ABSTRACT: Eyespot is an important disease of spring wheat (Triticum aestivum L.). Four species
of Ramulispora are associated with this disease, of which Tapesia yallundae and T.
acuformis. are common. This thesis investigates the broader subjects of genetic
variability, reproductive dynamics and fungicide resistance in Tapesia yallundae.
Each of the chapters treats specific but related topics. T. yallundae, which is the only
species thus far reported from South Africa, has been associated with yield losses of
up to 50%. To enable the implementation of more accurate and effective control
measures, understanding the dynamics of reproduction and the genetics of the
pathogen is of utmost importance. Of the many plant disease control measures such
as cultural practices, sanitation, biological control, etc., fungicide application is the
most commonly resorted to measure in eyespot control. This thesis investigates the
broader subjects of genetic variability, reproductive dynamics and fungicide
resistance of Tapesia yallzll7dae.
Fungicide application, however, is not without problems. The pathogen can
build up resistance to fungicides. The most commonly used fungicides in eyespot
control include the benzimidazole carbendazim, triazoles such as flusilazole,
tebuconazole, propiconazole, bromuconazole, flutriafol, fenbuconazole, triademinol,
and the imidazole, prochloraz. Cases of resistance to the groups listed above have
been reported. Frequent monitoring for resistance is thus crucial to prevent wastage
of fungicide and unnecessary impregnantation of the environment with potentially
ineffective chemicals. In chapter 2 of this thesis 300 isolates of T. yallundae from 15
fields were evaluated for resistance against carbendazim, flusilazole, tebuconazole,
propiconazole, bromuconazole, flutriafol and fenbuconazole. These results indicated
that to some triazoles, such as fenbuconazole, a high level of resistance was already
present in field populations.
In a sexually reproducing fungus such as T. yallundae, knowledge pertaining
to its ability to pass resistance factors to offspring is equally important. Mating
studies were, therefore, also conducted with parental strains that showed signs of
triazole resistance. Three generations were subsequently tested for resistance to five
triazoles, namely flusilazole, tebuconazole, propiconazole, bromuconazole and
flutriafol. Results of this study showed variable sensitivity in progeny, which
indicated quantitative inheritance of resistance to triazoles. Although the sexual stage has not yet been observed in the field in South Africa, this knowledge lays the
foundation for the long-term understanding of the population dynamics of the fungus.
The ability of a heterothallic ascomycete population to reproduce sexually is
dependent on the availability of its two mating types, MATI-I and MATI-2, their
distribution, and female fertility amongst other factors. In the UK. the teleomorph is
commonly observed in the field, which is in contrast to the situation in South Africa,
where it has only been induced in the laboratory. A comparative study between the
South African and the UK. populations was therefore undertaken. Isolates
representative of the two populations were mated with tester strains as both sperm
recipients and as sperm donors. This allowed the percentage of hermaphrodites to be
determined. No difference in terms of female fertility was observed between the
South African and the UK. populations, with both populations showing low effective
population numbers. These data suggested, therefore, that the teleomorph would also
occur more frequently in South Africa if the climate was more indusive to its
development.
The overall results of this study indicated that eyes pot could still be controlled
by means of fungicide application in South Africa. Although a shift in sensitivity was
observed towards fenbuconazole and flusilazole, no resistance was detected towards
carbendazim. The latter might be due to the absen<.:eof the sexual stage in the field,
coupled by the monocyclic nature of the pathogen and sensible fungicide regimes.
The absence of T. acujormis makes the disease situation less complicated in terms of
fungicide application and management. Continuous surveys will have to be
conducted, however, to monitor this situation in future. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die genetiese variasie, reproduksie dinamika en fungisied
weerstand in Tapesia yallundae. Elke hoofstuk handel oor spesifieke maar verwante
onderwerpe. Oogvlek is 'n belangrike siekte van lentekoring (Triticum aestivum L.).
Vier spesies van Ramulispora word geassosieer met die siekte, waarvan Tapesia
yallundae en T. acuformis mees algemeen voorkom. T. yallundae, wat tans die enigste
spesie is wat in Suid-Afrika aangeteken is, het al verliese van tot 50% veroorsaak. Om
meer akkurate en effektiewe beheermaatreels te implementeer, is dit noodsaaklik om die
oorlewingsdinamika van die patogeen te verstaan. Van al die siektebeheermaatreels soos
kulturele praktyke, sanitasie, biologiese beheer ens., bly fungisiedbehandeling die mees
algemene maatreel vir die beheer van oogvlek.
Fungisiedtoediening het egter ook verskeie probleme. Die patogeen kan
weerstand opbou teen die fungisied. Die mees algemene fungisiedes wat vir
oogvlekbeheer aangewend word sluit onder meer die benzimidasool karbendazim in,
triasole soos flusilasool, tebukonasool, propikonasool, bromukonasool, flutriafol,
fenbukonasool, triadimenol, en die imidasool, prochloraz. Weerstand is egter reeds teen
hierdie middels bekend. Gedurige monitering vir weerstand is dus krities om die
vermorsing van fungisied en besoedeling van die omgewing met oneffektiewe middels te
beperk. In hoofstuk 2 van hierdie manuskrip word 300 isolate van T. yallundae van 15
lande geevalueer vir weerstand teenoor karbendazim, flusilasool, tebukonasool,
propikonasool, bromukonasool, flutriafol en fenbukonasool. Resultate dui daarop dat
teen sommige van hierdie triasole, soos bv. fenbukonasool, daar reeds 'n hoe vlak van
weerstand teenwoordig was in veldpopulasies.
In 'n seksueel reproduserende fungus soos T. yalluJ1dae, is dit noodsaaklik om te
bepaal wat sy vermoe is om weerstandbiedenheid aan die nageslag oor te dra. Om die
rede is paringstudies ook op ouers wat tekens van weerstand teenoor triasole getoon het
uitgevoer. Drie generasies was gevolglik getoets vir weerstand teenoor vyf triasole,
naamlik flusilasool, tebuconasool, propikonasool, brumukonasool en flutriafol. Resultate
van die studie het 'n variasie in sensitiwiteit van die nageslag getoon, wat op 'n
kwantitatiewe oorerwing van weerstand teen £riasole dui. Alhoewel die teleomorf nog nie in lande in Suid-Afrika opgemerk is nie, Ie hierdie kennis die fondament vir die
langtermyn vertolking van die populasie dinamika van hierdie fungus.
Die vermoe van 'n heterotalliese askomiseet populasie om seksueel voort te plant
is afhanklik van die beskikbaarheid van sy twee paringstipes, MATI-I en MATl-2, hul
verpreiding, vroulike vrugbaarheid en ander faktore. Alhoewel die teleomorf algemeen
in lande in die Verenigde Koninkryk opgemerk word, is dit in kontras met die situasie in
Suid-Afrika, waar hierdie stadium nog slegs in die laboratorium gelnduseer kon word. 'n
Studie is dus onderneem om die Suid-Afrikaanse en V.K. populasies met mekaar te
vergelyk. Isolate van die twee populasies is dus gepaar met paringsisolate as beide sperm
ontvangers en sperm donors. Hierdie prosedure het dit moontlik gemaak om die
persentasie hermafrodiete te bepaal. Geen verskille in vroulike fertiliteit is tussen die
Suid-Afrikaanse en V.K. populasies bespeur nie, en beide populasies het ook 'n lae
effektiewe populasie getal getoon. Hierdie data het dus voorgestel dat die teleomorf ook
meer algemeen in Suid-Afrika sou voorkom as die klimaat meer geskik was vir teleomorf
vormmg.
Die resultate van hierdie studie het tot die slotsom gelei dat oogvlek steeds deur
fungisiedbehandeling in Suid-Afrika beheer kan word. Alhoewel daar 'n merkbare
verskuiwing in sensitiwiteit teenoor fenbukonasool en flusilasool was, was geen
weerstand teenoor karbendazim waargeneem nie. Laasgenoemde kan dalk toegeskryf
word aan die afwesigheid van die teleomorf in die veld, gekombineer met die
monosikliese natuur van die patogeen en gebruik van alternerende fungisiedes. Die
afwesigheid van T. acuformis maak die plaaslike siektetoestand minder gekompliseerd in
terme van fungisied aanwending en bestuur. Voortdurende opnames sal egter uitgevoer
moet word om hierdie situasie ook in die toekoms te monitor.
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Pathogenicity of fungi isolated from roots of sorghum seedlingsJones, Roger. January 1964 (has links)
Call number: LD2668 .T4 1964 J78 / Master of Science
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Seed-borne fungi of soybeans in KansasHabermehl, R. Wayne. January 1964 (has links)
Call number: LD2668 .T4 1964 H14 / Master of Science
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The biology of Endophyllum osteospermi, and its use for the biological control of Chrysanthemoides monilifera ssp. moniliferaWood, A. R. (Alan Robert) 12 1900 (has links)
Dissertation (PhD Agric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Chrysanthemoides monilifera ssp. monilifera is a shrub indigenous to South
Africa, which has become a serious weed of native vegetation in Australia. Endophyllum
osteospermi is a microcyclic, autoecious, rust fungus that induces witches' brooms on C.
monilifera ssp. monilifera. This rust is considered as a candidate biocontrol agent for use
against C. monilifera ssp. monilifera in Australia.
The vegetative growth and reproductive output of healthy branches on bushes
with different levels of E. osteospermi infections were measured at three sites. The
growth of healthy branches on infected bushes was 26- 81% less than that of healthy
branches on uninfected bushes. The number of buds, flowering capitulae, fruiting
capitulae, and cypselas on healthy branches of infected bushes was 35-75%, 45-90%,
15-99%, and 15-90% less, respectively, than those on uninfected bushes.
At five sites, the infection levels and number of witches' brooms were determined
every two months. The increase in number of witches' brooms per bush ranged between
o and 282 within one year, with an average increase per bush of28 (SE ± 4.8) and 39 (SE
± 9.2) during two years. The average simple interest rate (rs) increase of infection levels
for all bushes was 0.015 month-I (s.e. ± 0.0041, n = 72) and 0.0098 month" (s.e. ±
0.0073, n = 43) during two years.
Aecidioid teliospores germinated between 10 and 20oe, with 15°e as optimum.
Light, and particularly near-uv light, stimulated germination. A period of 6 to 8 hours of
light was needed to obtain optimum germination levels. The temperature requirements for
basidiospore development differed from that of aecidioid teliospore germination.
Optimum was at 15°e, but a rapid decrease in basidiospore production occurred at higher
temperatures, few developed at 19°e. Two nuclear divisions occurred within 12 hours of
germination to produce a metabasidium with three or four nuclei. A third nuclear division
occurred in the basidiospores between 24 and 48 hours. Plants inoculated under
controlled conditions took 5 to 24 months before witches' brooms began to develop.
A Geographic Information System (GIS) approach was used to model the
potential distribution of E. osteospermi in South Africa, based on monthly average
climate surfaces with parameters derived from the above experiments. The same model
was applied to Australia to suggest a potential distribution of the rust if released in Australia. This potential distribution was similar to one generated using the climate
matching computer programme CLIMEX©, but gave greater spatial accuracy. Both
approaches indicate that E. osteospermi should establish in temperate Australia.
Chrysanthemoides species, as well as other South African asteraceaus plants,
were monitored for E. osteospermi between 1992 and 2003. Endophyllum osteospermi
was recorded on C. monilifera ssp. monilifera, C. monilifera ssp. pisifera, C. monilifera
ssp. rotundata, C. monilifera ssp. canescens, C. monilifera ssp. subcanescens, C. incana,
an undescribed taxon of Chrysanthemoides, Osteospermum ciliatum, 0. polygaloides and
0. potbergense. Endophyllum dimorphothecae sp. nov. is described on Dimorphotheca
cuneata. Aecidium elytropappi, which was recorded on Elytropappus rhinocerostis and
Stoebe plumose, is transferred to Endophyllum as E. elytropappi comb. nov.
Germination of aecidioid teliospores and penetration by basidiospores were
observed on the surface of excised leaves of 32 plant species at 4 days after inoculation.
Germinating aecidioid teliospores aborted on 14 plant species, whilst no penetration was
attempted on a further 12. Penetration only occurred on 9. Therefore only these 9 plant
species need to undergo traditional host specificity testing. Pending these results, E.
osteospermi could be safely released in Australia for the biological control of C.
monilifera ssp. monilifera. / AFRIKAANSE OPSOMMING: Chrysanthemoides monilifera ssp. monilifera 'n meerjarige wat inheems in Suid
Afrika is, het 'n belangrike onkruid in Austalië geword. Endophyllum osteospermi 'n
mikrosikliese, autoecious roesswam, induseer heksebesems op C. monilifera ssp.
monilifera. Hierdie roesswam word as 'n potensiële biologiese beheeragent teen C.
monilifera ssp. monilifera in Austalië beskou.
Die vegetatiewe groei en voortplanting van gesonde takke op struike met
verskillende vlakke van E. osteospermi infeksies is by drie lokaliteite gemeet. Groei van
gesonde takke op geinfekteerde bosse was 26-81 % minder as die van gesonde takke op
ongeïnfekteerde bosse. Die aantalokselknoppe, blommende capitulum, vrugdraende
capitulum en pitvrugte op individuele gesonde takke van geïnfekteerde bosse was
onderskeidelik 35-75%, 45-90%,15-99%, en 15-90% minder, as die op ongeïnfekteerde
bosse.
By vyf lokaliteite is die infeksievlakke en die aantal heksebesems elke twee
maande vasgestel. Die toename in heksebesems van elke plant was tussen 0 en 282 binne
eenjaar, met 'n gemmidel van 28 (SE ± 4.8) en 39 (SE ± 9.2) geduurende twee jaare. Die
gemiddelde eenvoudige rentekoers (rs) toename in infeksievlakke van al die struike was
0.015 maand" (s.e. ± 0.0041, n = 72) en 0.0098 maand-1 (s.e. ± 0.0073, n = 43)
gedurende twee jaare.
Ontkieming van aecidioidteliospore het tussen 100e en 200e met 15°e as die
optimum. Lig en veral naby-uv lig het ontkieming gestimuleer, terwylontkieming relatief
swak was onder donker toestande. 'n Periode van 6 tot 8 uur lig was nodig vir optimale
ontkiemingsvlakke. Die temperatuurvereistes vir basidiospoor ontwikkeling het verskil
van die van aecidioid teliospoor ontkieming. Optimale was by 15°e, maar 'n vinnige
afname in basidiospoorproduksie het by hoër temperature voorgekom, min het by 19°e
voorgekom. Twee kernverdelings het binne 12 ure van die begin van ontkieming
voorgekom om 'n metabasidium te produseer met drie of vier kerne. 'n Derde kern
verdeling het in die basidiospore tussen 24 en 48 uur voorgekom. Plante wat onder
beheeerde toestande geïnokuleer is het heksebesems 5 tot 24 maande na inokulasie
ontwikkel. 'n Geografiese Inligtings Sisteem (GIS) benadering is gebruik om 'n model vir
die potensiële verspreiding van E. osteospermi in Suid Afrika te ontwikkel, gebasseer op
die maandelikse gemiddelde klimaatoppervlaktes met parameters wat vanaf bogenoemde
eksperimente verkry is. Dieselfde model is in Austalië toegepas om 'n potensiële
verspreiding van die roesswam voor te stel. Hierdie potensiële verspreiding was
soortgelyk aan 'n program wat met die klimaats vergelykende rekenaarsprogram
CLIMEX© ontwikel is, maar dit het groter ruimtelike akkuraatheid gemaak. Beide
benaderings het aangedui dat E. osteospermi in Austalië behoort te vestig.
Chrysanthemoides spesies, asook ander inheemse plante van die Asteraceae, is
tussen 1992 en 2003 vir die voorkoms van E. osteospermi in Suid Afrika waargeneem.
Endophyllum osteospermi is op C. monilifera ssp. monilifera, C. monilifera ssp. pisifera,
C. monilifera ssp. rotundata, C. monilifera ssp. canescens, C. monilifera ssp.
subcanescens, C. incana, 'n onbeskryfde taxon van Chrysanthemoides, Osteospermum
ciliatum, a. polygaloides en a. potbergense waargeneem. Endophyllum dimorphothecae
sp. nov. is beskryf op Dimorphotheca cuneata. Aecidium elytropappi, wat op
Elytropappus rhinocerostis en Stoebe plumosa voorkom, is by Endophyllum ingesluit as
E. elytropappi comb. nov.
Ontkieming van aecidioidteliospore en penetrasie deur basidiospore op die
oppervlak van verwyderde blare van 32 plant spesies 4 dae na inokulasie is waargeneem.
Ontkiemende aecidioidteliospore het op 14 toets plant spesies ge-aborteer, terwyl geen
penetrasie op 'n verdere 12 gepoog is nie. Penetrasie het slegs op 9 voorgekom. Derhalwe
hoef slegs die 9 plant spesies tradisionele gasheer spesifisiteitstoetse te ondergaan.
Afhangende van die resultate kan E. osteospermi dus met veiligheid in Austalië vir die
biologiese beheer van C. monilifera ssp. monilifera vrygelaat word.
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Metabolism of Colletotrichum lindemuthianum (Sacc. & Magn.) Scribner and infected Vigna sesquipedalis Fruw王易安, Wong, Yee-on, Pauline. January 1974 (has links)
published_or_final_version / Botany / Master / Master of Philosophy
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Reactions of three hundred corn families to pathogenic fungi at different locations in Kansas and MexicoTimti, Isidore Nse January 2011 (has links)
Digitized by Kansas Correctional Industries
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Development of the field bindweed bioherbicide, Phomopsis convolvulus : spore production and disease developmentMorin, Louise January 1989 (has links)
No description available.
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Cultural and other morphological studies of Inonotus arizonicusGoldstein, Donna Elizabeth January 1979 (has links)
No description available.
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