Thesis (MScAgric)--University of Stellenbosch / ENGLISH ABSTRACT: An understanding of the infection pathways of Botrytis cinerea in grape bunches will help
to combat this devastating pathogen of grape. Many studies have been done to determine the
possible infection pathways of B. cinerea. Most of these studies made use of artificial
inoculations that deposit groups of conidia on the plant surface. The deposition of clusters of
conidia is not a common phenomenon in nature. The aim of this study was to investigate the
infection pathways of (i) naturally- as well as (ii) artificially inoculated B. cinerea conidia
during all the phenological stages of three wine grape cultivars, and to compare the (iii)
pathogenicity and virulence, on grape and nectarine fruit, of isolates obtained from different
host plants.
In the natural infection study the occurrence of Botrytis cinerea and subsequent disease
expression at different positions in bunches of wine grapes (cultivars Chenin Blanc, Shiraz
and Chardonnay) was determined from 1999 to 2001. Different techniques were used to
detect viable inoculum at different positions (rachises, laterals, pedicels, and the peicel end,
cheek and style end of berries) in bunches. Isolations were made on Kerssies' B. cinerea
selective medium, or bunches were used untreated, or treated with paraquat. Paraquat was
used to terminate host resistance and to promote the development of the pathogen from the
tissues. The material was used untreated to detect the pathogen on the surface, or were
surface-sterilized to detect mycelia (latent infection) in the tissue. In the artificial inoculation
study, bunches of wine grapes (cultivars Chenin Blanc, Chardonnay and Shiraz) at pea size,
bunch closure, and harvest were dusted with dry conidia of Botrytis cinerea in a settling
tower and incubated for 24 h at high relative humidity (±93%). Following incubation, the
bunches were divided in two groups. The one group was surface-sterilised in 70% ethanol
for 5 s, the other group was left untreated. Bunches of the sterile group, and from the
untreated group were used for isolation. From each bunch rachis segments, laterals, pedicels
and berry skin segments (from the pedicel-end and cheek) were removed. The sections were
placed in Petri dishes on Kerssies' B. cinerea selective medium and on a water agar medium supplemented with paraquat, and incubated at 22°C under diurnal light. Occupation by the
pathogen was positively identified by the formation of sporulating colonies of B. cinerea on
the different tissues. Lastly, in the virulence and pathogenicity experiment on grape and
nectarine fruit Botrytis cinerea isolates, which were obtained from different host plants, were
compared by simulating natural infection. Cold-stored fruit, considered highly susceptible to
B. cinerea were therefore inoculated with single, airborne conidia of the pathogen. Different
tests were conducted to assess surface penetration and lesion formation. Isolations were
made from fruit skins on Kerssies' B. cinerea selective medium. Nectarine fruit were treated
with paraquat, and grape berries were frozen for 1 h at -12°C. Paraquat and freezing were
used to terminate host resistance and to promote the development of the pathogen from the
tissues.
In the natural infection studies B. cinerea occurred in a consistent pattern in bunches of the
three cultivars. B. cinerea consistently developed from the tissue of the rachis, laterals,
pedicel and pedicel-end, but not from the berry cheek. The rachis, lateral and pedicel
contained much higher levels of B. cinerea than any position on the berry. Furthermore, the
pathogen consistenly occurred at relatively high levels on the rachises throughout the season.
Collectively, the data showed that in the Western Cape province, B. cinerea occured more
regularly in wine grape bunches during the early part of the season, than later in the season.
The data of the artificial studies confirmed the findings made with the natural infection
studies. In these experiments the pathogen resided more often on the structural bunch parts
than on the berries. Overall, the isolation studies revealed that conidia occurred
predominantly on the rachis. The incidence of B. cinerea was furthermore constantly high in
the inner bunch after each inoculation, and in bunches of different maturities. The data
therefore indicated that, when available, conidia penetrated loose and tight clustered bunches
in a similar way. Finally, in the virulence and pathogenicity experiments the results showed
clearly that no host specialisation exists in the B. cinerea isolates used in this study.
From these studies it is clear that in the Western Cape province B. cinerea occurs more
readily in the inner structural parts of the bunches and more so during the earlier parts of the
season. These findings should be considered when planning and implementing disease
control programmes. / AFRIKAANSE OPSOMMING: INFEKSIEWEË VAN BOTRYTIS CINEREA OP GESELEKTEERDE WYNDRUIF
KULTIVARS
Indiepte kennis van die infeksieweë van Botrytis cinerea op druiwetrosse word benodig
vir die beheer van dié vernietigende patogeen van druiwe. Vele studies is al gedoen om die
moontlike infeksieweë van die swam op druiwe trosse te ondersoek. Die meeste van die
studies het gebruik gemaak van kunsmatige inokulasie tegnieke waar die konidia van die
swam in groepe op die korreloppervlak gedeponeer is. In die natuur is dit 'n rare verskynsel
dat konidia in groepe op die korreloppervlak land. Die doel van die studie was om die
infeksieweë van B. cinerea op drie wyndruif kultivars te ondersoek wat (i) natuurlik- en (ii)
kunsmatig geïnokuleer is met konidia gedurende al die fenologiese stadia, en om die (iii)
virulensie en patogenisisteit van isolate wat van verskillende gashere verkry is, op druiwe en
nektariens te vergelyk.
In die natuurlik-geïnokuleerde druiwe is die voorkoms van B. cinerea en die gevolglike
siektevoorkoms op verkillende posisies in trosse van wyndruiwe (Chenin Blanc, Chardonnay,
Shiraz) gedurende 1999 tot 2001 bepaal. Verskillende tegnieke is gebruik om lewensvatbare
inokulum by verskillende posisies (ragis, lateraal, pedisel en pedisel-end van die korrel) in
die tros waar te neem. Isolasies is op Kerssies' B. cinerea selektiewe medium gemaak, of
trosse is onbehandeld gebruik, of behandel met paraquat. Paraquat is gebruik om die gasheer
se natuurlike weerstand te verlaag en om die ontwikkeling van die patogeen te bevorder. Die
plantmateriaal is onbehandeld gelaat om die patogeen op die oppervlak waar te neem, of die
oppervlak is gesteriliseer om die latente myselium in die weefsel waar te neem. In die
kunsmatige inokulasiestudies is trosse, van wyndruiwe (Chenin Blanc, Chardonnay, Shiraz),
geïnokuleer met droë spore, van B. cinerea, in 'n inokulasietoring en die plantmateriaal is dan
geinkubeer vir 24 h by 'n hoë relatiewe humiditeit (93%). Na die inkubasie proses is die
trosse in twee groepe verdeel. Die een groep druiwe het oppervlak sterilisasie ondergaan in
70% etanol vir 5 s, en die ander groep was onbehandeld gelaat. Trosse van die onbehandelde
en gesteriliseerde groep druiwe is gebruik vir isolasies. Vanuit elke tros is daar segmente van
die ragis, laterale, pediselle en korrels (van die pedisel-end en wang gedeeltes) geïsoleer. Die segmente is in Petri bakkies met Kerssies' B. cinerea selektiewe medium en op water agar
medium, wat paraquat bevat het, geïsoleer en geïnkubeer onder 'n 12 h dagligperiode teen
22°C. Die patogeen is positief geïdentifiseer deur sporuierende kolonies op die onderskeie
weefseltipes. Laastens, in die virulensie- en patogenisiteitsproewe op druiwe en nektariens is
verskillende isolate van B. cinerea, verkry vanaf verskillende gasheerplante, vergelyk deur
natuurlike inokulasie toestande na te boots. Koue opgebergde vrugte, wat beskou word as
hoogs vatbaar vir die infeksie van B. cinerea, is geïnokuleer met droë, enkel luggedraagde
spore van die patogeen. Verskillende toetse is gedoen om die oppervlak penetrerende en
letselvormende vermoëns van die onderskeie isolate te toets. Isolasies is van die skille van
die vrugte gemaak en op Kerssies' B. cinerea selektiewe medium geplaas. Die
nektarienvrugte is met paraquat behandel en die druifkorrels is gevries vir 1 h teen -12°C.
Paraquat en bevriesing is gebruik om die gasheer se weerstand te verlaag en om die
ontwikkeling van die patogeen te bevorder.
In die natuurlik-geïnokuleerde studies het B. cinerea 'n konstante patroon getoon in die
trosse van die drie verskillende wyndruif kultivars. B. cinerea het konstant ontwikkel uit die
ragis, laterale, pedisel en pedisel-end, maar selde uit die korrelwang. Die ragis, lateral en
pedisel dele het baie hoër vlakke van van die swam bevat as enige deel op die korrel. Die
patogeen het ook konstant volop deur die hele seisoen op die ragis voorgekom. Gesamentlik
wys die data dat, B. cinerea in wyndruiwe, in die Wes Kaap provinsie, meer geredelik vroeër
in die seisoen voorkom, eerder as later.
Data van die kunsmatige inokulasiestudies het die bevindinge van die natuurlike
inokulasiestudies tot 'n groot mate bevestig. In dié studies het die patogeen meer geredelik
die strukturele dele van die tros, eerder as op die korrels, bewoon. Oor die algemeen het die
isolasieproewe gewys dat die konidia meer op die ragis voorkom as op enige ander deel. Die
voorkoms van B. cinerea was ook oor die algemeen baie hoër in die strukturele dele van die
tros, as op die korrel self. Die verskynsel het onder trosse van verskillende
ontwikkelingsvlakke voorgekom. Die data het dus ook gewys dat konidia, wanner dit
beskikbaar is, minder- sowel as meer kompakte trosse op 'n soortgelyke manier penetreer.
Laastens, in die virulensie en patogenisiteitseksperimente het die resultate duidelik gewys dat
daar geen gasheer spesifieke gedrag onder B. cinerea isolate is nie.
In die studies het dit duidelik na vore gekom dat, B. cinerea meer geredelik in die
strukturele binne dele van die wyndruif tros, in die Wes Kaap provinsie voorkom. En so ook eerder aan die begin van die seisoen, as later in die seisoen. Dié kennis moet in aanmerking
geneem word by die beplanning en implementering van siektebeheerprogramme.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52889 |
| Date | 12 1900 |
| Creators | Du Preez, Izak Frederik |
| Contributors | Holz, G., 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 | 91 p. |
| Rights | Stellenbosch University |
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