Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Grey mould, caused by Botrytis cinerea, is the most important foliar disease of rooibos
seedlings. Although the disease is primarily controlled with applications of fungicides, the
improvement of cultural methods of disease management should lessen this dependence on
chemical control. Such improvements would, however, not be possible without knowledge of
the inoculum sources and dispersal of the pathogen. The aim of this study was to investigate
the inoculum ecology of B. cinerea in rooibos nurseries in order to identify primary sources of
inoculum and to improve the environmentally friendly management of the disease.
The study was conducted in four nurseries over two production seasons (March to July
2003 and 2004). Levels of airborne inoculum of B. cinerea were monitored on a monthly basis
inside and around the nurseries with spore traps. Samples of plant material and organic debris
were taken in the corresponding areas to determine the incidence of plant material infected by
the pathogen and the incidences of grey mould in the nurseries were recorded. Low numbers
of B. cinerea colonies were observed on the spore traps. Similar levels of airborne inoculum
were observed inside and around the nurseries. The incidence of plant material yielding B.
cinerea was higher outside the nurseries than inside, indicating the importance of such
materials as potential sources of inoculum. Since patterns of airborne inoculum observed in
this study confirmed reports of the local dispersal of B. cinerea, the removal of possible hosts
outside the nurseries could aid in the management of grey mould in rooibos nurseries.
Resistance to dicarboximide fungicides is a genetically stable trait in B. cinerea, and
therefore has the potential to be used as a phenotypic marker. This marker can be used to gain
knowledge on the dispersal of B. cinerea inoculum inside and outside rooibos nurseries.
Isolates of B. cinerea collected from the air and from plant material in and around four rooibos
nurseries were assessed for resistance to iprodione at 1 and 3 μg/ml a.i. Some of the isolates
showed resistance to iprodione at 1 μg/ml a.i. However, none of the isolates showed resistance
at 3 μg/ml a.i. iprodione. The initial incidence of dicarboximide-resistance at the nurseries was
slightly higher than expected. As the season progressed, the incidence of iprodione-resistant
isolates decreased towards May, after which an increase was observed towards July. A
relatively high percentage of isolates collected outside the nurseries was found to be dicarboximide-resistant. Two of the nurseries had a significant higher incidence of resistant
isolates on plant material collected inside, than on plant material collected outside the nursery.
However, when looking at resistance levels of airborne isolates, no significant differences were
found in the incidence of resistant isolates sampled inside and outside the four nurseries. The
data indicated the importance of organic debris and seed-borne infections in the survival and
dispersal of dicarboximide-resistant isolates of the pathogen.
With the current emphasis on organic agriculture the knowledge gained in this study
presents valuable possibilities of improving the cultural management of grey mould in rooibos
nurseries. / AFRIKAANSE OPSOMMING: Vaalvrot, veroorsaak deur Botrytis cinerea, is die belangrikste bo-grondse siekte van
rooibossaailinge. Alhoewel die beheer van die siekte hoofsaaklik op die gebruik van
fungisiede berus, behoort die verbetering van verbouingspraktyke hierdie afhanklikheid van
chemiese beheer te verminder. Sulke verbeteringe sal egter slegs moontlik wees indien
voldoende kennis van die inokulumbronne en verspreiding van die patogeen beskikbaar is. Die
doel van hierdie ondersoek was om die inokulum ekologie van B. cinerea in rooibos kwekerye
te ondersoek sodat primêre inokulumbronne opgespoor en omgewingsvriendelike
siektebestuurspraktyke verbeter kan word.
Die ondersoek is in vier kwekerye oor twee produksie seisoene (Maart tot Julie 2003 en
2004) uitgevoer. Vlakke van luggedraagde inokulum van B. cinerea is op ’n maandelikse basis
met behulp van spoorvangers binne en buite die kwekerye gemonitor. Monsters van
plantmateriaal en organiese materiaal is in ooreenstemmende areas geneem om die voorkoms
van B. cinerea geïnfekteerde plantmateriaal vas te stel en die voorkoms van vaalvrot in die
kwekerye is aangeteken. Min B. cinerea kolonies is op die spoorvangers waargeneem.
Soortgelyke vlakke van luggedraagde inokulum is binne en buite die kwekerye waargeneem.
Die hoër voorkoms van B. cinerea geïnfekteerde plantmateriaal buite die kwekerye as binne,
dui op die belang van sulke materiaal as potensiële inokulumbronne. Aangesien die patrone
van luggedraagde inokulum, soos waargeneem in hierdie ondersoek, ander berigte van B.
cinerea se beperkte verspreidingsvermoë bevestig, kan die verwydering van moontlike
alternatiewe gashere buite die kwekerye die bestuur van die siekte binne die kwekerye
verbeter.
Weerstand teen dikarboksimied fungisiede is ’n geneties-stabiele kenmerk in B. cinerea
en het daarom potensiaal om as ’n fenotipiese merker gebruik te word. Hierdie merker kan
gebruik word om kennis aangaande die verspreiding van B. cinerea in en om rooibos kwekerye
in te samel. Botrytis cinerea isolate in lug en op plantmateriaal in en om vier rooibos
kwekerye is gedurende 2003 en 2004 versamel. Die isolate is vir weerstandbiedendheid teen
iprodioon by konsentrasies van 1 en 3 μg/ml aktiewe bestandeel (a.b.) getoets. Isolate met
weerstand teen 1 μg/ml a.b. iprodioon is waargeneem, maar nie teen 3 μg/ml nie. Die aanvanklike voorkoms van dikarboksimiedweerstand by die kwekerye was hoër as verwag.
Hierdie vlak het egter gedaal met die verloop van die seisoen tot in Mei, waarna ’n toename tot
in Julie waargeneem is. Die persentasie dikarboksimied-weerstandbiedende isolate buite die
kwekerye was relatief hoog. In twee van die kwekerye was die voorkoms van
weerstandbiedende isolate op plantmateriaal in die kwekerye betekenisvol hoër as op
plantmateriaal buite die kwekerye. Daar was egter geen betekenisvolle verskille in die
voorkoms van luggedraagde weerstandbiedende isolate nie, ongeag van die kwekery of posisie.
Die data dui op die belang van organiese materiaal en saadgedraagde infeksies in die oorlewing
en verspreiding van dikarboksimied-weerstandbiedende isolate van die patogeen.
Met die huidige klem op organiese landbou bied die inligting wat in hierdie ondersoek
versamel is moontlike praktyke wat geïmplementeer kan word om die beheer van vaalvrot in
kwekerye met behulp van verbouingspraktyke te verbeter.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20943 |
| Date | 04 1900 |
| Creators | Spies, Christoffel, F. J. (Christoffel Frederik Jakobus) |
| Contributors | Holz, G., Lamprecht, S.C., 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 | 66 leaves : ill. |
| Rights | Stellenbosch University |
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