Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Various studies revealed that Botrytis cinerea, the causal pathogen of Botrytis bunch
rot, is mostly associated with pedicels, rachises, laterals and berry bases, and not with berry
skins as previously understood. Provided that sufficient coverage of inner bunch parts was
achieved, laboratory studies have shown that fungicides can effectively reduce the amount of
B. cinerea at the various positions in bunches, and prevent infection and symptom expression
at all growth stages. The same efficacy was, however, not achieved with the same fungicides
when using conventional spraying methods in vineyards. Poor disease control on fruit and
leaves in vineyards is attributed to inappropriate timing of fungicide applications and/or
insufficient coverage of susceptible tissue. Previously, spray coverage evaluations in South
Africa were based on the use of water-sensitive cards. A variety of other methods have been
used to assess spray coverage in vineyards, but none of these methods could assess spray
deposits on a very small, three-dimensional area of interest such as the susceptible grape
bunch parts. The methods were furthermore dependent on human objectivity, which lacks
quantitative measuring and speed of measurement. Suitable technology to determine spray
coverage on susceptible bunch parts is, therefore, not available.
The aim of this study was to develop a protocol to visualise and quantify spray
deposits in grape bunches, specifically on the inner bunch parts and to use the protocol to
determine the effect of different levels of spray cover on artificially inoculated B. cinerea
grape bunches, in order to facilitate future determination of minimum effective coverage
levels for effective B. cinerea control.
A spray coverage assessment protocol using fluorometry, photomicrography and
digital image analyses was developed to measure spray coverage on susceptible grape bunch
parts. Among several fluorescent pigments tested, a yellow fluorescent pigment (SARDI
Fluorescent Pigment) from Australia was selected on the basis of its small particle size (2.45 -
4.90 μm). Bunches were sprayed at pea size and bunch closure with different volumes of a
mixture of fenhexamid and the yellow fluorescent pigment. Sprayed parts from bunches were
illuminated under black light (UV-A light in the 365 nm region) and visualised under a stereo
microscope at 20 x magnification. Photos of the berry skin, pedicel and rachis were taken
with a digital camera (Nikon DMX 1200). Image analysis of photos was done with Image-
Pro Discovery version 4.5 for Windows (Media Cybernetics) software. The total area of
deposited pigment in selected areas of interest (AOI) was calculated. The percentage area
covered was subsequently calculated for each AOI. Good correlation was evident between
the parameters, sum of objects and percentage area covered. Bunch parts at pea size generally
had higher coverage values than at bunch closure. Spray applications earlier in the season
would therefore result in higher and more effective spray coverage of the susceptible bunch
parts. Similar deposition trends were observed on the inner bunch parts (pedicel and rachis).
These were, however, significantly different from berry skins, which had significantly higher
levels of spray deposits than the inner bunch parts. The variance component analysis
indicated that the highest variance was observed for berries and bunches, and substantially
less for image readings. For the same accuracy, means for percentage coverage values of at
least 10 bunches per treatment (1 part per bunch and 3 readings per part) will be sufficient.
In order to determine the biological efficacy of different levels of spray coverage on B.
cinerea incidence on grape bunches, bunches were sprayed at pea size and bunch closure with
different volumes of a mixture of fenhexamid and a yellow fluorescent pigment and the
percentage fluorescent pigment coverage on pedicels was determine. Bunches were
subsequently dusted with dry airborne conidia of B. cinerea in a settling tower and incubated
for 24 h at high relative humidity (98%). Infection was determined by estimating the amount
of B. cinerea infections occurring on sprayed bunch parts with isolations on to paraquat and
Kerssies mediums. Linear regressions for the part x stage combinations of percentage B.
cinerea incidence on different bunch parts were fitted on mean coverage levels. An increase
in spray cover caused linear reductions in levels of B. cinerea on susceptible bunch parts.
Higher B. cinerea incidences were recorded at pea size. Furthermore, higher B. cinerea
incidences were found on paraquat medium for both stages, than on Kerrsies medium. The
information gathered from this study will be used to facilitate future determination of
minimum effective coverage levels for effective B. cinerea control in grape bunches.
In these validation experiments, the results clearly showed that the protocol can be
used to determine the effect of different levels of spray coverage on B. cinerea incidence and
that an increase in spray coverage will decrease B. cinerea incidence. The information
gathered from this study will be used to facilitate future determination of minimum effective
coverage levels for effective B. cinerea control in grape bunches and subsequently be used as
benchmarks to evaluate spray application in vineyards. / AFRIKAANSE OPSOMMING: Vaalvrot by wingerde word veroorsaak deur Botrytis cinerea. Verskeie studies het
getoon/gewys dat die oorsaaklike patogeen meestal geassosieer word met die pedisel, ragis,
laterale en die korrelbasis, en nie met die korrelskil soos voorheen beweer nie. Laboratorium
studies het getoon dat swamdoders wel effektief is om B. cinerea by alle trosdele te verminder
en simptoomontwikkeling te voorkom tydens alle groeistadia, mits die binne-trosdele
voldoende spuit bedekking ontvang het. Dieselfde effektiwiteit is egter nie gevind in
wingerde met konvensionele spuittegnieke nie. Onvoldoende siektebeheer van vrugte en
blare van wingerde kan toegeskryf word aan verkeerde spuit skedulering en/of swak
spuitbedekking van vatbare gasheerweefsel. Evaluering van spuitbedekking is voorheen in
Suid Afrika deur middel van water-sensitiewe papier gedoen. Verskeie ander metodes is al
gebruik om spuitbedekking te evalueer in wingerde, maar nie een van hierdie metodes kan
gebruik word om spuitbedekking op ’n baie klein, drie-dimensionele oppervlak, soos die
vatbare trosdele, te evalueer nie. Verder was die tegnieke afhanklik van menslike
objektiwiteit, en gevolglik ontbreek kwantitatiewe meting en metingspoed. Daar is dus nie
geskikte tegnologie vir die evaluering van spuitbedekking op vatbare trosdele nie.
Die doel van hierdie studie was die ontwikkeling van ‘n protokol vir die visualisering
en kwantifisering van spuitbedekking op spesifiek die binne-tros dele en om die protokol dan
te gebruik om die effek van verskillende vlakke van spuitbedekking op B. cinereageinokuleerde
druiwetrosse te bepaal,
Protokol vir evaluasie van spuitbedekking op vatbare druifdele is ontwikkel deur
gebruik te maak van fluorometrie, fotomikrografie en digitale beeldanalise. Van die
verskillende fluoresensie pigmente wat getoets is, is ‘n geel flouresensie pigment (SARDI
Flourescent Pigment) van Australië gekies op grond van sy klein partikelgrootte (2.45 - 4.90
μm). Druiwetrosse is gespuit tydens ertjie- en trostoemaakstadia met verskillende volumes
van ’n mengsel van fenheksamied en die geel fluorosensie pigment. Die gespuite druifdele is
dan verlig onder swartlig buise (UV-A lig in die 365 nm spektrum) en gevisualiseer deur ’n
stereo mikroskoop by 20x vergroting. Foto’s van die korrelskil, pedisel en ragis is met ‘n
digitale kamera (Nikon DMX 1200) geneem. Beeldanalise is gedoen met ImagePro
Discovery weergawe 4.5 vir Windows (Media Cybernetics) sagteware. Die totale area
neerslag van die pigment is in geselekteerde areas bereken. Die presentasie area bedek is
bereken vir elkeen van hierdie areas. Goeie korrelasie is gevind tussen die parameters aantal
fluoresserende partikels en die persentasie bedekte area. Trosdele tydens ertjie-stadium het in
die algemeen hoër waardes gehad as by trostoemaak. Dit blyk dus dat spuittoediening vroeg
in die seisoen meer effektief sal wees vir die bedekking van vatbare trosdele. Soortgelyke
bedekkings patrone is gevind by die binne trosdele (pedisel en ragis). Dit het egter
betekenisvol verskil van die korrelskil, wat betekenisvol meer spuitbedekking as die binne
trosdele gehad het. ’n Variasie komponent analise het getoon dat die meeste variasie gevind
is tussen korrels en trosse, en heelwat minder vir die beeld analise lesings. Om dieselfde
akkuraatheid te behou, is ten minste 10 trosse per behandeling (1 deel per tros en 3 lesings per
deel) nodig.
Vir die bepaling van biologiese effektiwiteit van verskillende vlakke van
spuitbedekking op B. cinerea voorkoms op druiwe, is druiwe gespuit tydens ertjie- en
trostoemaak-stadia met verskillende volumes van ’n mengsel van fenheksamied en die geel
fluorosensie pigment. Die persentasie fluoresensie pigment is bepaal op die pedisels. Trosse
is vervolgens geinokuleer met droë luggedraagde konidia van B. cinerea in ’n inokulasietoring
en geïnkubeer vir 24 h by hoë relatiewe humiditeit (98%). Die voorkoms van B.
cinerea infeksie op gespuite tros dele is bepaal deur middel van isolasies op paraquat en
Kerssies medium. Liniêre regressies vir trosdeel x stadium kombinasies van persentasie B.
cinerea voorkoms op verskillende trosdele is gepas vir gemiddelde bedekkings waardes. ’n
Verhoging in spuit bedekking het ‘n liniêre vermindering van B. cinerea voorkoms op vatbare
trosdele veroorsaak. Verder is hoër vlakke van B. cinerea op paraquat medium as op Kerssies
medium vir beide die groeistadia gevind. Die kennis wat verkry is uit hierdie studie sal
gebruik word om minimum effektiewe spuitbedekkingsvlakke vir die beheer van B. cinerea
op druiwetrosse te bepaal.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20915 |
| Date | 04 1900 |
| Creators | Brink, Jan-Cor (Johannes Cornelius) |
| Contributors | Fourie, Paul H., Holz, Gustav, 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 | 46 leaves |
| Rights | Stellenbosch University |
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