Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The Cape Floristic Region (CFR) of South Africa is well-recognised for exceptionally high plant
species diversity and endemism. However, little attention has been bestowed on the pests
and pathogens in this region, even though these may greatly influence plant distribution and
evolution. In this study we identify various arthropods and fungi as pests and diseasecausing
organisms of the ecologically and economically important CFR-endemic tree taxa of
Virgilia. We isolated, identified and determined the pathogenicity of key fungal taxa from
diseased Virgilia trees throughout the CFR. In addition we evaluated the role of possible pest
arthropod taxa, including bark beetles, phoretic mites, larvae of a cerambycid beetle and
larvae of the endemic Leto venus (ghost moth), in the death of Virgilia trees. Key fungal
taxa were identified by comparisons of the internal transcribed spacer rDNA regions of the
isolated taxa with those available on GenBank. Pathogenicity of the most commonly
encountered fungal taxa was determined both in the field and under greenhouse conditions.
Five different disease symptoms were observed on Virgilia trees throughout the CFR. At
Table Mountain, Virgilia oroboides subsp. oroboides showed symptoms of: (1) several small
cankers on stems, seemingly caused by a Fusarium acuminatum-like fungus, (2) a root rot
disease caused by Armillaria mellea and (3) small bracket fungi on stems associated with
Schizophyllum commune. Virgilia oroboides from the Harold Porter National Botanical
Garden was diagnosed with a root disease consistently associated with an un-described
Phomopsis species. Virgilia oroboides subsp. ferruginea and V. divaricata from Knysna and
the Tsitsikamma area often showed symptoms of rapid wilting and death. The Virgilia stems
were damaged by the tunnelling larvae of the ghost moth and those of an unidentified
cerambycid beetle. Galleries and the surrounding wood tissues often housed the
ophiostomatoid fungi Ceratocystis tsitsikammensis and Ophiostoma plurianulatum. These
seem to originate from nitidulid beetles found feeding on gum exudate. Pathogenicity trials
confirmed the virulence of the undescribed Phomopsis species, the F. acuminatum-like
fungus, S. commune and C. tsitsikammensis to Virgilia. All four morpho-species of bark
beetles found in this study, together with phoretic mites on two of the beetle morphospecies,
were only collected from dead and dying Virgilia hosts and were classified as
secondary pests. Both beetle taxa and mites commonly carried spores of various Geosmithia
spp. These are not pathogenic to Virgilia trees, but may be an important food source for the bark beetles, as it dominated the fungal community in galleries. The phoretic mites were
unable to feed on their Geosmithia associates, but have been observed to feed on dead bark
beetle larvae within galleries. This suggests that the relationship of bark beetles, mites and
their associated Geosmithia species in this system is complex and in need of further study.
Our results show that natural populations of Virgilia play host to numerous destructive
pathogens, some of which are non-native (e.g. A. mellea) and a cause for special concern.
Additionally, the isolation of the undescribed Phomopsis species and A. mellea from
botanical gardens, with A. mellea now spreading to natural areas, calls for stricter control
over the movement of organic material from these areas. / AFRIKAANSE OPSOMMING: Die Kaapse Floristiese Streek (KFS) van Suid-Afrika is bekend vir buitengewoon hoë
plantspesie-diversiteit en endemisme. Min aandag is egter tot dusver geskenk aan die peste
en patogene in hierdie streek, al mag hulle plantverspreiding en evolusie dramaties
beinvloed. In hierdie studie identifiseer ons verskeie geleedpotige diere en fungi as peste en
organismes wat siektes veroorsaak in die ekologies en ekonomies belangrike, KFS-endemiese
boom genus Virgilia. Ons het die sleutel fungi vanaf Virgilia oor die hele KFS geisoleer,
geidentifiseer en hulle patogeniteit bepaal. Addisioneel het ons ook die rol van moontlike
pes geleedpotiges, insluitende baskewers, cerambycid kewerlarwes en die endemiese Leto
venus (spookmot) in die dood van Virgilia bome geevalueer. Sleutel fungi taksa is
geidentifiseer deur die interne getranskribeerde spasieerder rDNS streke van die geisoleerde
taksa met die wat op GenBank beskikbaar was te vergelyk. Patogenisiteit van die mees
algemeen geisoleerde fungi taxa is beide in die veld en onder glashuis-toestande bepaal. Vyf
verskillende siekte simptome is by Virgilia bome regdeur die KFS waargeneem. By Tafelberg
het Virgilia oroboides subsp. oroboides simptome getoon van: (1) verskeie klein kankers op
stamme, blykbaar veroorsaak deur ‘n Fusarium acuminatum-agtige fungus, (2) ‘n wortelvrot
siekte veroorsaak deur Armillaria mellea en (3) klein rakswamme op stamme geassosieer
met Schizophyllum commune. Virgilia oroboides in die Harold Porter Nationale Botaniese
Tuin is gediagnoseer met ‘n wortelvrot siekte wat altyd met ‘n onbeskryfde Phomopsis
spesie geassosieer is. Virgilia oroboides subsp. ferruginea and V. divaricata van Knysna en
die Tsitsikamma area het dikwels simptome getoon van vinnige verwelking en dood. Die
Virgilia stamme is deur die tonnelende larwes van die spookmot en dié van ‘n
ongeidentifiseerde cerambycid kewer beskadig. Galerye en die omringende houtweefsel het
dikwels die ophiostomatoid fungi Ceratocystis tsitsikammensis en Ophiostoma plurianulatum
gehuisves. Dit lyk asof hierdie fungi van nitidulid kewers afkomstig is wat op die
gomuitskeidings gevoed het. Patogeniteitsproewe het die kwaadaardigheid van die
onbeskryfde Phomopsis spesie, die F. acuminatum-agtige fungus, S. commune en C.
tsitsikammensis teenoor Virgilia bevestig. Al vier morfo-spesies baskewer wat in hierdie
studie gevind is, sowel as die foretiese myte op twee van die kewer morfo-spesies, is slegs
van dooie of sterwende Virgilia gashere versamel, en is as sekondêre peste geklassifiseer. Beide kewerspesies en myt taksa het algemeen spore van verskeie Geosmithia spesies
(Geosmithia pallida, G. flava, G. microcorthyli, G. sp. 1 en G. sp. 2) gedra. Die Geosmithia
spesies is nie patogenies teenoor Virgilia bome nie, maar mag ‘n belangrike voedselbron vir
die baskewers wees, aangesien dit die fungus-gemeenskap in die galarye gedomineer het.
Die foretiese myte was nie instaat om op Geosmithia-assosiate te voed nie, maar is
waargeneem om op dooie baskewer larwes te voed binne die galerye. Dit stel voor dat die
verhouding van die baskewers, myte en hulle geassosieerde Geosmithia spesies in die
sisteem kompleks is, en verdere studie benodig. Ons resultate dui aan dat natuurlike
populasies van Virgilia gashere is vir verskeie destruktiewe patogene, sommige waarvan nieinheems
(bv. A. mellea) wat ‘n bron van groot kommer is. Verder noodsaak die isolasie van
die Phomopsis spesie en A. mellea, wat beide wortelvrot siektes in botaniese tuine
veroorsaak, strenger kontrole oor die verskuiwing van organiese materiaal uit hierdie areas,
veral gegewe dat A. mellea reeds na natuurlike areas versprei het. / The Centre of Excellence In Tree Health Biotechnology for a bursary and funding the research conducted in this study
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/79902 |
| Date | 03 1900 |
| Creators | Machingambi, Netsai |
| Contributors | Roets, Francois, Dreyer, Leanne L., Roux, Jolanda, Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xiv, 156 p. : col. ill., maps |
| Rights | Stellenbosch University |
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