Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Botrytis cinerea Pers.: Fr., a pathogen of grapevine (Vitis vinifera L.), moves mainly
through conidia by air currents in vineyards which are deposited intermittently on the
surfaces of leaves, inflorescences and bunches. Little is known about the relationship between
the inoculum dosage in air and incidence of Botrytis bunch rot, and how the relationship is
influenced by environmental and host factors. To better understand this relationship,
information is needed on the period over which conidia have accumulated, the time they are
able to survive and remain infectious, time of symptom expression in relation to conidium
arrival at the infection court and host surface wetness. The aims of this study were (i) to
estimate the amount of viable B. cinerea occurring in air in vineyards, and at different
positions on leaves, inflorescences and bunches of grape at different phenological stages, (ii)
to determine the relationships between the number of B. cinerea colonies recorded on spore
traps placed in the bunch zone of vines and the incidence of B. cinerea recorded from the
different tissues, and (iii) to compare the efficacy of fenhexamid on leaves and inflorescences
carrying natural B. cinerea inoculum with those inoculated with dry, airborne conidia.
Different techniques were used to detect viable Botrytis cinerea in air currents and on
plant material obtained from table (cultivars Dauphine and Waltham Cross in Paarl- and
Worcester-district) and wine grape (cultivars Chardonnay, Sauvignon Blanc and Merlot in
Stellenbosch- and Malmesbury district) vineyards in the Western Cape province during
2001-02 and 2002-03. For four consecutive days during prebloorn, bloom, pea-size, bunch
closure, veraison and harvest, sets of Petri dishes with freshly prepared Kerssies' B. cinerea
selective medium (spore traps) were left overnight in the bunch zone of vines. Plant material
was collected from the vines on the fourth day. Leaves, infloresence and bunches were
treated with paraquat to terminate host resistance and to promote the development of the
pathogen on the tissues. The B. cinerea inoculum dosage in air, and the incidence at which
the pathogen was detected at various positions on leaves and in bunches normally differed
between vineyards. However, the various tests revealed that the pathogen generally occurred
in a consistent pattern in air in the bunch zone of vines, on leaves and in bunches from all
vineyards. The inoculum dosage in air in the bunch zone of the vine was generally highest
during prebioom or during bloom, it decreased at pea size and mostly remained at a very low
level at the later growth stages. The estimations of viable B. cinerea residing naturally on leaves and in bunches, showed that their amounts depicted levels occurring in air in the bunch
zone of the vine. Necrotic leaves occurring early season in vineyards were identified as an
important source of secondary inoculum for dispersal to the developing bunches. Latent
infections at the various positions in bunches were few at véraison and harvest. However, due
to the necrotrophic ability of the pathogen, extensive berry rot (due to berry-to-berry contact)
and thus severe bunch rot developed from a single berry that become symptomatic at the base
of the pedicel/berry attachment zone. The B. cinerea occupation pattern explains why
Botrytis bunch rot develops mostly from the inner bunch and why disease management
strategies should concentrate on the bloom to pre-bunch closure stage and on inhibiting B.
cinerea development in the inner bunch during the early part of the season. Thus, to
effectively reduce B. cinerea in grapevine, preventative applications are recommended to
reduce two primary infection events: (a) between budding and pre-bloom to counteract
primary leaf infection; (b) during late bloom or early pea size stage, to reduce the amount of
the pathogen on leaves and infloresences and to prevent colonisation of floral debris. A third
spray can be applied at bunch closure to reduce the amount of B. cinerea at various positions
of the inner bunch, especially for cultivars with tight bunches.
The efficacy of fenhexamid on leaves and inflorescences carrying natural B. cinerea
inoculum was compared with those inoculated with dry, airborne conidia. Shoots were
obtained during late bloom from a vineyard (wine grape cultivar Merlot) in the Stellenbosch
region. The shoots were divided into two main groups. One group of shoots was left
uninoculated, the other shoots were inoculated by dusting with dry B. cinerea conidia in a
settling tower. Before inoculation, equal numbers of shoots in each main group was sprayed
with fenhexamid, or left unsprayed. Following inoculation and incubation, shoots of each
treatment were divided in two equal groups. The one lot of shoots were rinsed in water. The
other lot of shoots were immersed in paraquat solution to terminate host resistance and to
promote the development of the pathogen from the tissues. For both uninoculated and
inoculated shoots, irrespective of fungicide treatment, leaves remained asymptomatic at both
the blade and petiole position for the water rinse treatment. No symptom of B. cinerea decay
developed at any of the positions on leaves from shoots sprayed with fenhexamid. Spraying
of shoots with fenhexamid completely suppressed B. cinerea infection and symptom
expression on both uninoculated and inoculated inflorescens. For inoculated shoots, B.
cinerea developed from approximately 50% of the laterals in the water rinse treatment.
However, inflorescences rinsed in water remained asymptomatic. The laboratory studies showed that fungicides, if applied properly to shoots and bunches
under controlled conditions, effectively reduced the amount of B. cinerea at the various
positions on leaves and inflorescence, and prevented infection and symptom expression at
bloom. However, these goals are not achieved in vineyards where the fungicides are applied
by conventional spraying methods. Therefore, more work is needed to evaluate fungicide
application techniques by conventional spraying methods for proper fungicide coverage, and
the reduction of B. cinerea in bunches. / AFRIKAANSE OPSOMMING: Botrytis cinerea Pers.: Fr., 'n patogeen van druiwe (Vilis vinifera L.), beweeg hoofsaaklik
deur middel van konidia in lugstrome deur die wingerd, en word dan afwisselend op die
oppervlakte van die blare, bloeiwyses en trosse gedeponeer. Daar is nog min bekend oor die
verhouding tussen die hoeveelheid inokulum in die lug en die voorkoms van Botrytis op die
trosse, en hoe die verhouding deur omgewings- en gasheerfaktore beïnvloed word. Ten einde
hierdie interaksie beter te verstaan, word inligting benodig oor die tydperk waarin die konidia
akkumuleer, die tyd wat hulle oorleef en virulent bly, en die tyd van simptoom-uitdrukking in
verhouding tot die verspreiding van die konidia by die infeksie-setel en benatbaarheid van die
gasheer-oppervlakte. Die doel van hierdie studie was (i) om die hoeveelheid lewensvatbare B.
cinerea wat in die lug voorkom, asook by verskeie posisies op blare, bloeiwyses en trosse by
verskillende fenologiese stadiums te kwantifiseer, (ii) om die verhouding tussen die aantal
aangetekende B. cinerea kolonies op spoorvangers wat in die trossone van die wingerd
geplaas is, en die voorkoms van B. cinerea, aangeteken van verskeie weefsels, te bepaal, en
(iii) om die effektiwiteit van fenhexamid op blare en bloeiwyses wat natuurlike B. cinerea
inokulum dra, te vergelyk met dié wat met droë, luggedraagde konidia geïnokuleer is.
Verskillende tegnieke is gebruik om lewensvatbare Botrytis cinerea in lugstrome en op
plantmateriaal van tafeldruiwe (kultivars Dauphine en Waltham Cross In Paarl- en
Worcester-distrik) en wyndruiwe (kultivar Chardonnay, Sauvignon Blanc en Merlot in
Stellenbosch- en Malmesbury distrik) in wingerde van die Wes-Kaap provinsie gedurende
2001-02 en 2002-03 te kwantifiseer. Petri bakkies met vars voorbereide Kerssies medium,
selektief vir B. cinerea (spoorvangers), is vir vier agtereenvolgende dae gedurende
vóórblom, blom, ertjiekorrel, trostoemaak, kleurbreek en oes, oornag in die trossone van
wingerdstokke in betrokke wingerde, gelaat. Plantmateriaal is op die vierde dag versamel.
Blare, bloeiwyses en trosse is met paraquat behandel ten einde die gasheerweerstand af te
breek en ontwikkeling van die patogeen op die weefsel te bevorder. B. cinerea inokulum in
die lug, en die frekwensie waarby die patogeen op verskeie posisies op blare en in die trosse
voorgekom het, het normaalweg tussen wingerde verskil. Die verskeie toetse het getoon dat
die patogeen normaalweg in 'n vaste patroon in die lug en die trossones van wingerde, asook
op blare en in trosse van alle wingerde voorkom. Die inokulumkonsentrasie in die lug in die
trossones van wingerdstokke was normaalweg die hoogste gedurende vóórblom of gedurende blom. Die inokulumdruk het by ertjiekorrel verminder en meestal by 'n 'n baie lae vlak
tydens die latere groeistadia gebly.
Die bepaling van lewensvatbare B. cinerea wat natuurlik op blare en in trosse gedeponeer
is, het getoon dat hul hoeveelhede ooreenstem met vlakke wat in die lug in die trossone van
die wingerd voorkom. Nekrotiese blare vroeg in die seisoen is 'n belangrike bron van
sekondêre inokulum en speel dus 'n belangrike rol by die verspreiding van Botrytis tussen die
ontwikkelende trosse. Latente infeksies by die verskeie posisies in trosse was laag by
kleurbreek en oes. Weens die saprofitiese vermoëns van die patogeen, kan uitgebreide
korrelvrot (a.g.v. korrel-tot-korrel kontak) en dus ernstige trosvrot, ontwikkel. 'n Enkele
korrel kan by die basis van die pedisel/korrel vashegtingsone simptomaties raak, en vandaar
na aangrensende korrels versprei. Die B. cinerea kolonisasiepatroon verduidelik waarom
Botrytis trosvrot meestal vanaf die binneste tros ontwikkel en waarom siektebeheerstrategieë
op die vóórblom- tot blomstadium gekonsentreer moet word, en op die inhibering van B.
cinerea ontwikkeling in die binneste tros gedurende die vroeë stadia van die seisoen. Dus, om
B. cinerea effektief tydens die twee primêre infeksie stadiums in wingerde te verminder, kan
voorkomende toedienings aanbeveel word: (a) tussen knopvorming en vóórblom om primêre
blaarinfeksie te verhoed; (b) gedurende láátblom en vroeë ertjiekorrel om die hoeveelheid
inokulum op die blare en bloeiwyses te verminder, en die kolonisasie van blomdebris te
voorkom. 'n Derde toediening kan tydens trostoemaak aangewend word om B. cinerea by
verskeie posisies in die binneste tros te verminder, veral by kultivars met digte trosse.
Die effektiwitiet van fenhexamid op blare en bloeiwyses waarop natuurlike B. cinerea
inokulum voorkom is vergelyk met dié wat met droë, luggedraagde konidia geïnokuleer is.
Lote is vanaf 'n wingerd (wyndruif kultivar Merlot) in die Stellenbosch distrik tydens
láátblom verkry en in twee hoofgroepe verdeel. Die een groep lote is geïnokuleer deur droë
B. cinerea konidia in 'n afsettingstoring te strooi, terwyl die ander groep nie geïnokuleer is
nie. Vóór inokulasie, is die helfte van die lote in elke groep met fenhexamid behandel, terwyl
die ander helfte onbehandeld gelaat is. Ná inokulasie en inkubasie, is lote van elke
behandeling verder in twee eweredige groepe verdeel. Die een groep lote is in water gespoel,
terwyl die ander groep lote in 'n paraquatoplossing gedompel is om die gasheerweerstand te
verwyder, en die ontwikkeling van die patogeen vanuit die weefsels te bevorder. Vir die
waterspoelbehandeling van beide ongeïnokuleerde en geïnokuleerde lote, ongeag van die
fungisiedbehandeling, het die blare asimptomaties by beide die bladoppervlakte en blaarsteelposisie gebly. Geen simptome van B. cinerea verrotting het by emge van die
blaarposisies van die lote, met fenhexamid gespuit, ontwikkel nie. Die spuit van die lote met
fenhexamid het die B. cinerea infeksie en die simptoomontwikkeling op beide die
ongeïnokuleerde en geïnokuleerde bloeiwyses heeltemalonderdruk. By die geïnokuleerde
lote, het B. cinerea vanaf ongeveer 50% van die laterale in die waterspoelbehandeling
ontwikkel, alhoewel, bloeiwyses wat in water afgespoel is, heeltemal asimptomaties gebly
het.
Laboratoriumstudies het getoon dat fungisiedes, indien korrek toegedien op lote en trosse
onder gekontroleerde toestande, tot effektiewe vermindering van B. cinerea getalle by die
verskillende posisies op blare en bloeiwyses lei, en infeksie en simptoomuitdrukking tydens
blom voorkom. Weens die feit dat die doelwitte nie behaal kan word in wingerde waar die
fungisiede deur konvensionele spuitmetodes toegedien is nie, moet meer studies gedoen word
om fungisied toedieningstegnieke, by konvensionele spuitmetodes, VIr deeglike
fungisiedbedekking en die vermindering van B. cinerea in trosse, te evalueer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50138 |
| Date | 03 1900 |
| Creators | Van Schoor, Jan Adriaan |
| 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 | English |
| Type | Thesis |
| Format | 111 p. |
| Rights | Stellenbosch University |
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