Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Botrytis bunch rot of grape is caused by Botrytis cinerea Pers. :Fr. Conidia of the
pathogen, which is dispersed by wind, water droplets and by insects, can penetrate the intact
grape berry cuticle, but disease expression occurs only under predisposing conditions. Since
relatively high infection rates often occur in vineyards, predisposing factors must play a
fundamental role in primary infection and subsequent disease occurrence. Insects can play a
very important role in this regard by depositing inocula at wound sites during feeding and by
providing fresh wounds during their oviposition and feeding activities. The aim of this study
was (i) to determine the potential of the Mediterranean fruit fly to transfer B. cinerea and
other bunch and fruit rot fungi in natura, (ii) to investigate the transport, deposition and
subsequent disease expression on grape berries in vitro, and (iii) to investigate fruit fly
activities and the nature of deposited conidia and mycelia of B. cinerea by aid of digital
photography and epifluorescence microscopy, respectively.
Two Sensus fruit fly traps containing the para-pheromone, Capilure, were installed in
orchards and five neighboring vineyards on four farms in the Stellenbosch region. Ceratitis
fruit flies were collected weekly, identified and counted to determine the fluctuations in fruit
fly population. Following field collection, the fruit flies were plated on Kerssies' B. cinerea
selective medium and the number of flies yielding the pathogen was recorded. Two fruit fly
species, C. capitata and C. rosa, were captured during the study period. Ceratitis rosa
numbers comprised only 1% of the total number of fruit flies captured. Ceratitis capitata
numbers, and the percentage B. cinerea contaminated flies generally increased after harvest in
the different orchards and vineyards. Following harvest, the percentage flies yielding B.
cinerea was higher in vineyards compared to orchards. Furthermore, in each vineyard an
increase in percentage B. cinerea contaminated fruit flies was preceded by a corresponding
increase in its neighboring orchard. The levels of both Penicillium and Alternaria
contaminated fruit flies stayed high throughout the investigation period, especially after
harvest of the orchard cultivars. Low incidence of Aspergillus, Mucor and Rhizopus spp.
were recorded on C. capitata. These findings suggest that the Mediterranean fruit fly may play an important role in the dispersal of inocula of fungi associated with postharvest decay
from early-maturing stone fruit orchards to mid- and late-maturing wine grape vineyards, and
in disease induction under conditions unfavourable for natural infection.
Three experiments were conducted to determine the potential of fruit flies in provoking B.
cinerea decay. In the first experiment, transport of conidia and disease expression were
investigated on rachis segments bearing unwounded berries only. In the second experiment,
the effect of wounding on disease expression was investigated. In the third experiment, the
effect of inoculum type (mycelia and conidia) on transportation and disease expression was
investigated on rachis segments bearing unwounded berries, and on segments with wounded
berries. The table grape cultivar, Dauphine, and the wine grape cultivar, Shiraz, were used at
véraison, two weeks before harvest and harvest, and the transport studies were conducted in
ethanol-disinfected perspex cages. Disease expression was studied in dry (~56% RH),
ethanol-disinfected perspex chambers incubated at 22°C. The isolations from berries revealed
that the flies deposited, without preference, high amounts of B. cinerea at various positions on
the grape berry's surface. The freezing studies showed that the deposited conidia germinated
and penetrated the berry skin at various positions. However, B. cinerea developed more often
at the pedicel end than on the cheek or style end, which indicated a peculiar interaction
between B. cinerea, the fruit fly and host tissue at this part of the berry. This phenomenon
was substantiated by the finding that B. cinerea also developed more often at the pedicel end
of berries that were not frozen. Further evidence for this interaction was found on intact
berries exposed to flies that carried mycelia after feeding on berries without sporulating
colonies of the pathogen, but showing symptoms of slippery skin. Significantly more decay
developed on wounded berries compared to the unwounded berries and more so at the wound
site. In addition, female fruit flies were responsible for significantly more decay development
than male fruit flies. The study thus proved that the Mediterranean fruit fly can promote B.
cinerea disease development under conditions unfavorable to natural infection.
The activities of the Mediterranean fruit fly, Ceratitis capitata, on grape berries were
monitored by aid of digital photography. In addition, the deposition of conidia and mycelia of
Botrytis cinerea at three sites (pedicel end, cheek and style end) on the grape berry,
germination of the fungal structures after dry (±56% RH) and moist (±93% RH) incubation
and wounds inflicted during ovipositioning were examined with an epifluorescence
microscope. The observations revealed that the fruit fly's activities were generally restricted to the grape berry. They visited the grape berry cheek more often, but visitations to the
pedicel end of berries increased substantially from véraison to harvest, indicating the
possibility of nutrient leakages at this site. Microscopy revealed that the flies deposited
conidia singular, in feeding packages and in faecal excrements on the berry surface. The
conidia in feeding packages were ensheathed by salivical fluids and occurred in clusters of 10
to 50 conidia. An average of 60% of the conidia in feeding packages germinated under dry
conditions (±56% RH). Conidia that passed through the intestinal tract of the fruit fly and that
were deposited in faecal excrements were deformed and low in viability. These conidia did
not occur in cluster format, but were proportionally spread with the faeces on the surface of
the grape berry. Conidia that were deposited singular and in faecal excrements did not
germinate unless incubated under moist conditions (± 93% RH). Wounds inflicted by female
fruit flies during ovipositioning were most frequently observed on the cheek. This
predisposition to B. cinerea infection of grape berries by the activities of fruit flies, suggested
an important role for the flies in the initiation of Botrytis bunch rot epidemics in vineyards. / AFRIKAANSE OPSOMMING: DIE ROL VAN DIE MEDITERREENSE VRUGTEVLIEG, CERATITIS CAPITATA,
IN BOTRYTIS CINEREA TROSVERROTTING VAN DRUIWE
Botrytis-trosverrotting van druiwe word deur Botrytis cinerea Pers. :Fr. veroorsaak.
Konidia van die patogeen wat deur wind, waterdruppels en insekte versprei word, kan die
intakte druiweskil binnedring, maar siekte-uitdrukking vind slegs onder spesiale
omstandighede plaas. Aangesien relatief hoë infeksie vlakke algemeen in wingerde voorkom,
moet predisponerende faktore 'n fundamentele rol in die primêre infeksie, en die daaruit
voortspruitende siektetoestand speel. Insekte kan 'n baie belangrike bydrae lewer deur
inokuia tydens voeding by wonde te deponeer. Nuwe wonde kan ook tydens oviposisionering
en voeding ontstaan. Die doel van hierdie studie was om (i) die potensiaal van die
Mediterreense vrugtevlieg om B. cinerea en ander tros- en vrugverrottingswamme in natura
oor te dra, te bepaal; om (ii) die verspreiding, deponering en daaropvolgende siekteuitdrukking
op druiwekorrels in vitro te ondersoek; en om (iii) die aktiwiteite en aard van die
gedeponeerde konidia en miselia met behulp van digitale fotografie sowel as epifluoressensiemikroskopie
waar te neem.
Twee Sensus-vrugtelokvalle met die paraferomoon, Capilure, IS In vrugteboorde en
aangrensende wingerde in die Stellenbosch-omgewing aangebring. Ceratitis-vrugtevlieë is
weekliks versamel, geïdentifiseer en getel om fluktuasies in die vrugtevliegpopulasie te
bepaal. Na die veldversameling is die vrugtevlieë op Kerssies se B. cinerea-selektiewe
medium uitgeplaat. Gedurende die studie is twee spesies vrugtevlieë, C. capitata en C. rosa,
gevang. Na oesstyd het die aantal Ceratitis-vrugtevlieë en die persentasie vrugtevlieë, besmet
met B. cinerea, in die verskillende boorde en wingerde toegeneem. Na oestyd was die
persentasie vrugtevlieë wat B. cinerea gedra het, hoër in die wingerde as in die boorde. Elke
toename in die persentasie B. cinerea-besmette vrugtevlieë in 'n wingerd is voorafgegaan
deur 'n ooreenkomstige toename in die aangrensende vrugteboord. Die aantal vrugtevlieë
besmet met Penicillium en Alternaria spp. het tydens die navorsingstydperk deurgaans hoog
gebly, veral nadat die vrugteboord-kultivars geoes is. Die voorkoms van Aspergillus-,
Mucor- en Rhizopus spp. op Ceratitis-vrugtevlieë was deurgaans laag. Hierdie bevinding wys
daarop dat vrugtevlieë 'n belangrike rol speel in die verspreiding van swarninokula, wat met na-oes verrotting geassosieer word, van vroegrypwordende steenvrugteboorde na mid- en
laatrypwordende wyndruifwingerde.
Drie eksperimente is in vitro onderneem om vrugtevlieë se potensiaal om B. cinereaverrotting
te veroorsaak te bepaal. In die eerste eksperiment is ragi met slegs ongewonde
korrels gebruik om die oordrag van konidia en siekte-ontwikkeling te ondersoek. In die
tweede eksperiment is die effek van verwonding op siekte-ontwikkeling ondersoek. In die
derde eksperiment is die effek van inokulumtipe (miselia en konidia) op verspreiding en
siekte-ontwikkeling ondersoek deur ragis-segmente met gewonde korrels sowel as ragissegmente
met ongeskonde korrels te gebruik. Die tafeldruif-kultivar Dauphine en die
wyndruif-kultivar Shiraz, by kleurbreuk, twee weke voor oes en by oestyd, is in die
eksperimente gebruik. Die oordragstudies is in etanol-ontsmette perspex-hokke uitgevoer.
Siekte-ontwikkeling is bestudeer in droeë (±56% RH), etanol-ontsmette perspex-kamers en
geinkubeer by 22°C. By ondersoek is gevind dat vlieë, sonder voorkeur, groot hoeveelhede
B. cinerea op verskeie dele op die druiwekorrel-oppervlak deponeer. Bevriesingstudies het
aangetoon dat die gedeponeerde konidia op verskeie dele van die korrelontkiem en die skil
binnedring. Botrytis cinerea het egter meer dikwels by die korrelsteelkant as by die
stempelkant, of op die wang, ontwikkel. Hierdie bevinding het 'n eiesoortige interaksie
tussen B. cinerea, die vrugtevlieg en gasheerweefsel by die korrelsteelkant van die korrel
aangetoon. Die verskynsel is gestaaf deur die bevinding dat B. cinerea ook meer dikwels by
die korrelsteelkant van die korrels wat nie gevries is nie, ontwikkel het. Verdere bewys van
hierdie interaksie is gevind by ongeskonde korrels wat aan die vlieë wat miselia gedra het
blootgestel is. Die siekte het beduidend meer dikwels op gewonde as ongewonde korrels en
verder aansienlik meer dikwels op die wondoppervlakte ontwikkel. Dit was ook duidelik dat
vroulike vrugtevlieë baie meer vir verrotting verantwoordelik was as manlike vrugtevlieë.
Die studie bewys dus dat Mediterreense vrugtevlieë die ontwikkeling van B. cinerea kan
bevorder in omstandighede wat ongunstig is vir natuurlike infeksie.
Die aktiwiteite van die Mediterreense vrugtevlieg C. capitata op die druiwekorrels is met
behulp van digitale fotografie waargeneem. Verder is die deponering van konidia en miselia
van B. cinerea op die verskillende dele (korrelsteelkant, wang en stempelkant) van die korrel,
ontkieming van die swamstrukture na droeë (±56% RH) en nat (±93% RH) inkubasie en
wonde wat tydens oviposisionering veroorsaak is, met epifluoressensie-mikroskopie
ondersoek. Die waarnemings het onthul dat die vrugtevlieg se aktiwiteite gewoonlik tot die druiwekorrel beperk is. Hulle het korrelwange meer dikwels besoek. Besoek aan die
korrelsteelkant het aansienlik toegeneem van kleurbreuk tot oestyd, wat op die moontlikheid
van voedingstof-lekkasie by die deel aandui. Mikroskoopstudies het aangedui dat vlieë
konidia enkel, in voedingspakkies en in fekale uitskeidings op die korreloppervlakte
deponeer. Die konidia in die voedingspakkies is deur speekselvloeistof omhul en het in
groepe van 10 tot 50 konidia voorgekom. Gemiddeld 60% van die konidia in
voedingspakkies het in droeë omstandighede (±56% RH) ontkiem. Konidia wat deur die
spysverteringskanaal van die vrugtevlieg gegaan het en in die fekale ekskresie gedeponeer is,
was misvorm en het lae lewensvatbaarheid gehad. Laasgenoemde konidia was nie in groepe
gedeponeer nie, maar is proporsioneel met die feces op die oppervlak van die druiwekorrel
versprei. Konidia wat enkel en in feces gedeponeer is, het nie ontkiem nie, tensy toestande
vogtig (±56% RH) was. Wonde wat deur die vroulike vrugtevlieë tydens oviposisionering
veroorsaak is, is meer dikwels op die wang van die korrelopgemerk. Hierdie predisposisie
van druiwekorrels tot B. cinerea-infeksie, meegebring deur die aktiwiteit van die vrugtevlieg,
dui daarop dat die rol wat die vrugtevlieg in die inisiëring van Botrytis trosverrottingepidemies
in wingerde speel, van beduidende belang is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53168 |
| Date | 03 1900 |
| Creators | Engelbrecht, Rene |
| Contributors | Holz, G., Pringle, K. L., 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 | 118 p. : ill. |
| Rights | Stellenbosch University |
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