Dissertation (PhD (Agric))--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Fungi belonging to the genus Botryosphaeria are heterotrophic micromycetes that can be
pathogens on woody plants. They cause serious, and in some cases devastating losses to
crops through leaf necrosis, stem cankers and plant death. The Proteaceae cut-flower
industry in South Africa accounts for 70% of the national cut-flower enterprise.
Botryosphaeria diseases are a major impediment to production and trade of Proteaceae
and there is an urgent need to investigate the etiology, epidemiology and control of these
diseases. Losses of one of the most important proteas, P. magnifica, amount to 50% or
more, locally. The main aims of this study were therefore to establish the etiology and
aspects of epidemiology of Botryosphaeria stem cankers on P. magnifica and other
Proteaceae, and to investigate methods of disease control.
Although there is a vast body of information pertaining to this fungus, which was
reviewed in Chapter 1, there is relatively little information available on Botryosphaeria
on Proteaceae. The taxonomy of Botryosphaeria requires thorough review, and
molecular techniques need to be employed to resolve species identities.
In Chapter 2, it was found that Phyllachora proteae, a leaf pathogen of proteas,
produced a Fusicoccum anamorph, which is described as F. proteae. A sphaeropsis-like
synanamorph was associated with F. proteae and a new combination for P. proteae is
proposed in Botryosphaeria, as B. proteae.
The taxonomy of Botryosphaeria is in disarray at both the generic and the specific
level. In Chapter 3 the taxonomic history of Botryosphaeria is reviewed, and the genus
circumscribed and distinguished from other morphologically similar genera. Although
several anamorph genera have been linked to Botryosphaeria, based on morphological
observations and phylogenetic analysis of lTS rDNA sequence data, two anamorph
genera are now recognised, those with pigmented conidia (Diplodia), and those with
hyaline conidia (Fusicoccum). Botryosphaeria proteae should thus be excluded from
Botryosphaeria.
Several pathogenic Botryosphaeria spp. have an endophytic phase within their
hosts. They are therefore imported unwittingly into other countries where they may pose
a risk to agriculture and indigenous vegetation. The current global distribution of Botryosphaeria spp. associated with Proteaceae is clarified and a key to these taxa
associated with Proteaceae is provided in Chapter 4. Five Botryosphaeria spp. are
associated with cut-flower Proteaceae worldwide viz. B. lute a, B. obtusa, B. protearum,
B. proteae and B. rib is. B. protearum is described as a new species.
A thorough understanding of disease epidemiology is essential to effect a
reduction of losses. In Chapter 5, I show that on P. magnifica, lesions caused by
Botryosphaeria protearum, which lead to the formation of stem cankers, are initiated in
the mid-rib vein or margin of leaves. Koch's postulates were satisfied and it was found
that the number of lesions that developed from artificial inoculations correlated with
starch levels present in leaves at the time of inoculation.
In Chapter 6 it is shown that B. protearum exists as an endophyte in leaves of P.
magnifica in naturally occurring as well as cultivated plants. In natural stands of proteas
stem cankers are rare, but in cultivated plantations the incidence is high. Nutritional
analyses indicate that higher levels of nitrogen occur in leaves of cultivated plants in
spring, which could enhance disease development. High levels of sodium in the leaves of
wild plants may restrict disease development.
The severe economic losses caused by B. protearum make the search for
improved methods of disease control essential. Fungicide applications form an important
component of an integrated approach to disease management. In Chapter 7, in vitro tests
demonstrate that tebuconazole, benomyl, prochloraz me, iprodione and fenarimol reduce
the mycelial growth of B. protearum effectively. In the field there was a 25-85%
reduction in the occurrence of stem cankers by applying fungicides or sanitation pruning.
The best control was achieved by using benomyl, bitertanol, fenarimol, iprodione,
prochloraz manganese chloride alternated with mancozeb and tebuconazole
prophylactically. If sanitation pruning is combined with regular applications of
fungicides, disease can be combated. / AFRIKAANSE OPSOMMING: Mikrofungi wat tot die genus Botryosphaeria behoort, is heterotrofiese organismes, wat
patogenies op houtagtige plante kan wees. Hulle veroorsaak ernstige, en in sommige
gevalle, verwoestende verliese, deur blaarnekrose, stamkankers en plantafsterwing. Die
Proteaceae snyblom-industrie in Suid-Afrika maak 70% van die nasionale snyblomindustrie
uit. Botryosphaeria siektes is 'n belangrike struikelblok in die produksie en
handeldryf van Proteaceae, en daar is 'n ernstige behoefte om die etiologie,
epidemiologie en beheer van siektes te ondersoek. Verliese van een van die belangrikste
proteas, P. magnifica, beloop plaaslik 50% of meer. Die hoof doelstellings van hierdie
studie was dus om die etiologie en epidemiologie van Botryosphaeria stamkankers op P.
magnifica en ander Proteaceae vas te stel en metodes van siektebeheer te ondersoek.
Hoewel daar 'n wye hoeveelheid inligting rakende die swam bestaan, wat in
Hoofstuk I hersien is, is daar relatief min inligting oor Botryosphaeria op Proteaceae
beskikbaar. Die taksonomie van Botryosphaeria benodig deeglike hersiening, en
molekulêre tegnieke word benodig om spesie-identiteite op te klaar.
In Hoofstuk 2 is gevind dat Phyllachora proteae, 'n blaarpatogeen van proteas, 'n
Fusicoccum anamorf produseer, wat as F. proteae beskryf word. 'n Sphaeropsis-agtige
synanamorf is met F. proteae geassosieer en 'n nuwe kombinasie vir P. proteae is as B.
proteae in Botryosphaeria voorgestel.
Die taksonomie van Botryosphaeria is, beide op die genus- as die spesievlak, in
wanorde. In Hoofstuk 3 word die taksonomiese geskiedenis van Botryosphaeria hersien,
en die genus word omskryf en van ander morfologies soortgelyke genera onderskei.
Hoewel verskeie anamorf genera al met Botryosphaeria op grond van morfologiese
waarnemings en filogenetiese analise van ITS rDNA volgorde data verbind is, word twee
anamorf genera nou herken, dié met gepigmenteerde konidia (Diplodia), en dié met
deurskynende konidia (Fusicoccum). Botryosphaeria proteae moet dus van
Botryosphaeria uitgesluit word.
Verskeie patogeniese Botryosphaeria spp. het 'n endofitiese fase in hul
lewenssiklus. Hulle word dus onwetend in ander lande ingevoer waar hulle 'n gevaar vir
landbou en inheemse plantegroei kan inhou. Die huidige wêreldverspreiding van Botryosphaeria spp. wat met Proteaceae geassosieer word is opgeklaar, en in Hoofstuk 4
word 'n sleutel tot die taksa wat met Proteaceae geassosieer word verskaf. Vyf
Botryosphaeria spp. word met snyblom Proteaceae wêreldwyd geassosieer, naamlik B.
lutea, B. protearum, B. proteae, B. ribis en B. obtusa. B. protearum word as 'n nuwe
spesie beskryf.
'n Deeglike kennis van siekte-epidemiologie is noodsaaklik ten einde verliese te
verminder. In Hoofstuk 5 dui ek aan dat letsels wat lei tot stamkankers, veroorsaak deur
Botryosphaeria protearum op P. magnifica, in die hoofnerf of rant van blare ontstaan.
Koch se postulate is uitgevoer en daar is vasgestel dat die aantal letsels wat vanuit
kunsmatige inokulasies ontwikkel het korreleer met die styselvlakke teenwoordig in die
blare ten tye van die inokulasie.
In Hoofstuk 6 word getoon dat B. protearum as 'n endofiet in die blare van P.
magnifica. In natuurlike standplase van proteas is stamkankers skaars, maar in verboude
plantasies is die voorkoms hoog. Voedingsanalises dui aan dat hoër vlakke van stikstof
in die blare van verboude plante in die lente voorkom, wat siekte-ontwikkeling moontlik
kan bevorder. Hoë vlakke van natrium in die blare van natuurlike plante mag siekteontwikkeling
beperk.
Die ernstige ekonomiese verliese wat deur B. protearum veroorsaak word, maak
die soektog na verbeterde metodes van siektebeheer noodsaaklik. Fungisiedtoedienings
maak 'n belangrike deel uit van 'n geïntegreerde benadering tot siektebeheer. In
Hoofstuk 7 dui in vitro toetse aan dat tebuconazole, benomyl, prochloraz me, iprodione
en fenarimol die miseliumgroei van B. protearum effektief verminder. 'n Vermindering
van 25-85% is aangetoon in die voorkoms van stamkankers in die veld, deur die
toediening van fungisiedes en sanitasiesnoei. Die beste beheer is verkry deur die
voorkomende toediening van benomyl, bitertanol, fenarimol, iprodione en prochloraz
manganese chloride, afgewissel met mancozeb en tebuconazole, op plante in die veld.
Indien sanitasiesnoei met gereelde toedienings van fungisiedes gekombineer word, kan
die siekte bekamp word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52721 |
| Date | 03 1900 |
| Creators | Denman, Sandra |
| Contributors | Crous, P. W., Wingfield, M. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 170 p. : ill. |
| Rights | Stellenbosch University |
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