Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Petri disease and esca are devastating grapevine trunk diseases and compromise the
sustainability of viticulture world-wide. Despite being extensively studied, knowledge of
inoculum sources and mechanisms of spread of the causal pathogens is limited. Arthropods
have been suspected to play a role in the spread of Petri disease and esca pathogens.
However, little information is known about the extent to which arthropods are associated
with these pathogens. This study aimed to determine whether arthropods occurring within or
on declining grapevines, are associated with trunk disease pathogens and to identify
arthropods associated with pruning wounds. The potential of selected arthropods to act as
vectors of trunk disease pathogens was also investigated.
Two vineyards exhibiting grapevine trunk disease infections were sampled weekly
for two years for collection of arthropods. Arthropods were collected using pruning wound
traps, visual searches as well as trunk and cordon traps. Fungal spores from surfaces of
arthropods were collected in water. Samples were subjected to nested PCR using primers
Pm1/Pm2 and Pch1/Pch2 to verify the presence of Phaeoacremonium spp. and
Phaeomoniella chlamydospora, respectively. Water samples were also cultured and
grapevine trunk disease pathogens obtained were identified by sequencing the internal
transcribed spacers 1 and 2 and the 5.8S rRNA gene or the partial beta-tubulin gene. A total
of 10 875 arthropod individuals, belonging to more than 31 families, were collected from
declining grapevines. The most abundant arthropods included millipedes, ants, spiders and
beetles. Portuguese millipedes and cocktail ants were associated with fresh grapevine
pruning wounds. Thirty-three percent of the 5677 water samples analysed, contained
propagules of pathogens associated with Petri disease and esca. Of these, 37 % were
recovered from millipedes, 22 % from cocktail ants, 15 % from spiders and 10 % from
beetles. All the major groups of grapevine trunk diseases were detected on the arthropods. Phaeoacremonium species were detected in 1242 samples while Phaeomoniella
chlamydospora was identified from 855 samples. Other fungi isolated included members of
the Botryosphaeriaceae, Diatrypaceae and Diaporthales.
The potential of grapevine sap as a food source for Portuguese millipedes and
cocktail ants was investigated, in vitro. Millipede individuals were offered a choice between
water and grapevine sap while ants in nests were presented with grapevine sap, tuna and
water and monitored for ingestion of sap. Both taxa preferred grapevine sap over the other food items, indicating close association with pruning wounds. Subsequently, the ability of
both taxa to transmit a DsRed-transformed Phaeomoniella chlamydospora isolate to fresh
pruning wounds of canes in polystyrene strips, floating in water, and potted vines was
tested. Arthropods were exposed to the fungus for 24 hours and transferred to the base of the
plants and canes and were removed after three days. Isolations after a month revealed that
millipedes and ants were capable of transmitting the fungus onto wounds and cause
infection. Millipede faecal pellets were also evaluated as potential sources of inoculum.
Millipedes were fed on Phaeomoniella chlamydospora for 24 hours, surface sterilised and
allowed to defaecate in sterile Petri dishes overnight. Faecal material was collected,
macerated in water and plated onto potato dextrose agar. Propagules of Phaeomoniella
chlamydospora survived passage through the gut of millipedes and were passed out in a
viable state to form colonies of Phaeomoniella chlamydospora.
This study concludes that a wide variety of arthropods can be a source of inoculum
of trunk diseases in vineyards. The results of the dissemination trial provides evidence that
millipedes and ants are able to disseminate and infect vines with Phaeomoniella
chlamydospora. It is therefore, highly likely that other grapevine trunk disease pathogens
are transmitted in the same manner. This knowledge highlights the need for control of
certain arthropods to be taken into consideration when managing grapevine trunk disease
pathogens. / AFRIKAANSE OPSOMMING: Petri siekte en esca is verwoestende wingerd stamsiektes en verhinder die
volhoubaarheid van wingerdproduksie wêreldwyd. Hierdie siektes is al intensief bestudeer,
maar kennis rakende die inokulum bronne en meganismes van verspreiding van die
veroorsakende patogene is beperk. Arthropoda is al vermoed om ‘n rol te speel in die
verspreiding van Petri siekte en esca patogene, maar weinig informasie is bekend oor die
mate waartoe arthropoda geassosieer is met die patogene. Hierdie studie het ten doel gestel
om die arthropoda wat op of in wingerdstokke wat terugsterf voorkom te identifiseer en te
bepaal watter van die arthropoda geassosieer is met stamsiekte patogene. Daar is ook ten
doel gestel om die arthropoda wat geassosieer is met vars snoeiwonde te identifiseer en ook
die moontlike vektor status van die stamsiekte patogene deur arthropoda.
Arthropoda is weekliks vir twee jaar gekollekteer vanaf twee wingerde met
stamsiekte infeksies. Snoeiwond lokvalle, visuele soektogte en stam- en kordon lokvalle
was gebruik om arthropoda te vang. Swamspore van die oppervlak van die arthropoda is
afgewas met water. Van hierdie water monsters is gebruik om dubbelvoudige polimerase
ketting reaksies (PKR) te doen met die inleiers Pm1/Pm2 en Pch1/Pch2 om vir die
teenwoordigheid van Phaeoacremonium spp. en Phaeomoniella chlamydospora
onderskeidelik te toets. Die oorblywende water monster is gekweek op medium om die
swamme teenwoordig te bepaal. Die wingerd stamsiekte patogene is verder geidentifiseer
deur die DNS volgordes te bepaal van die interne getranskribeerde spasies 1 en 2 en die
5.8S rRNS geen of ‘n gedeelte van die beta-tubulien geen. In totaal is 10 875 arthropoda,
wat behoort tot 31 families, gekollekteer vanaf wingerde wat terugsterf. Die mees algemene
arthropoda was duisendpote, miere, spinnekoppe en kewers. Die Portugese duisendpote en
die wipstert mier is geassosieer met vars wingerd snoeiwonde. Van die 5677 water monsters wat geanaliseer is, het 33% propagules van die Petri siekte of esca patogene gehad. Van
hierdie was 37 % afkomstig vanaf duisendpote, 22 % van wipstert miere, 15 % van
spinnekoppe en 10 % van kewers. Al die hoofgroepe van wingerd stampatogene is
opgespoor op die arthropoda. Phaeoacremonium species is opgespoor in 1242 monsters en
Phaeomoniella chlamydospora is gevind in 855 monsters. Ander swamme wat ook geisoleer
is sluit lede van die Botryosphaeriaceae, Diatrypaceae en Diaporthales in.
Die potensiaal van wingerdsap as ‘n bron van voedsel vir Portugese duisendpote en
wipstert miere is in vitro ondersoek. Duisendpoot invidue is ‘n keuse gegee tussen water en wingerd sap terwyl mierneste ‘n keuse gehad het tussen water, wingerd sap en tuna. Die
duisendpote en miere is gemonitor vir die inname van wingerdsap in die teenwoordigheid
van die ander bronne. Beide die duisendpote en miere het wingerdsap verkies wat aandui dat
hulle ‘n noue assosiasie met wingerd snoeiwonde het. Vervolgens is beide taksons getoets
vir hul vermoë om ‘n DsRooi-getransformeerde Phaeomoniella chlamydospora isolaat te
vektor na vars snoeiwonde op lote gemonteer op polistireen stroke wat in water dryf en op
wingerd plante in potte. Die duisendpote en miere is blootgestel aan die swam vir 24 uur en
oorgedra na die basis van die plante en lote en is weer verwyder na drie dae. Na ‘n maand is
isolasies gedoen wat gewys het dat die duisendpote en miere die swam suksesvol kon oordra
na die snoeiwonde en infeksie veroorsaak. Duisendpoot uitwerpsels is geëvalueer vir die
potensiaal as inokulum bron. Duisendpote het gevoed op Phaeomoniella chlamydospora vir
24 uur, daarna oppervlakkig gesteriliseer en toegelaat om oornag uitwerpsels te maak in
steriele Petri bakkies. Uitwerpsels was gekollekteer, fyngemaak in water en op aartappel
dekstrose agar uitgeplaat. Propagules van Phaeomoniella chlamydospora het die
verteringskanaal van die duisendpote oorleef en het tipiese kolonies op die agar gevorm.
Hierdie studie het vasgestel dat ‘n verskeidenheid van arthropoda ‘n bron van
inokulum van stamsiektes in wingerd kan wees. Die resultate van die vektor proewe het
gewys dat duisendpote en miere die vermoë het om Phaeomoniella chlamydospora te
versprei na snoeiwonde wat die swam dan suksesvol geinfekteer het. Dit is daarom hoogs
waarskynlik dat van die ander wingerd stamsiekte patogene ook versprei kan word op
dieselfde manier. Hierdie kennis demonstreer dat die beheer van spesifieke arthropoda in ag
geneem moet word in die bestuur van wingerd stamsiektes. / Winetech, Agricultural Research Council of South Africa and NRF for financial support
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80224 |
| Date | 03 1900 |
| Creators | Moyo, Providence |
| Contributors | Mostert, L., Halleen, F., 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 | Unknown |
| Type | Thesis |
| Format | iv, 114 p. : ill. |
| Rights | Stellenbosch University |
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