Thesis (MScAgric)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Ripgut brome (Bromus diandrus Roth.) is a weed that causes great problems
in the most wheat and grain producing areas and also in livestock practices.
Until recently (1995) there were no registered chemicals for the management
of ripgut brome in wheat, in South Africa. After the registration of sulfosulfuron
and iodosulfuron + mesosulfuron for the management of ripgut brome in
wheat, these two herbicides were widely used and in the case of wheat
monocultures, it was used repeatedly. During the last few years, reports of
ripgut brome that were suspected to be resistant to these chemicals,
increased. With the development of herbicide resistance it is of great
importance to investigate methods to confirm resistance and also to control it.
The goal of this study was firstly, to confirm resistance in ripgut brome and
secondly to compare growth and development of resistant ripgut brome
popualtions to that of susceptible ripgut brome populations. The dormancy of
Bromus seed was also investigated as were effective methods to break seed
dormancy. Lastly, quicker methods to confirm resistance were investigated.
A short summary of the experiments follows.
In the first experiment the degree of resistance of three different ripgut brome
populations were determined, by using the pot spray method. One population
each of B. pectinatus and B. rigidus were also included in the study. The
seed of the Bromus populations were germinated after which it was planted in
plastic pots and were placed in the glasshouse until the three to four leaf
stage. Subsequently the plants were treated with the following four herbicides:
sulfosulfuron, iodosulfuron + mesosulfuron, imazamox and haloxyfop-R
methyl ester, at seven concentrations namely, the recommended dosage, one
quarter, one half, twice, four times and eight times the recommended dosage.
After six weeks the percentage survival and the dry mass of the plants were
determined. Results showed that the three ripgut brome populations had
different degrees of resistance to sulfosulfuron and iodosulfuron +
mesosulfuron, varying from no resistance to moderate resistance to strong
resistance. There was no resistance to imazamox and haloxyfop-R methyl ester. The B. rigidus population exhibited strong resistance or tolerance
(natural resistance) to the two sulfonylureum herbicides.
In the second experiment the seed of the same Bromus populations were
germinated and planted in plastic pots that were filled with three litres of river
sand to determine the growth, development and seed production of the plants.
The number of leaves for each plant as well as the plant height were
measured weekly, until the plants became reproductive. The two resistant
populations grew much faster than the susceptible population and they also
produced taller plants. The susceptible population produced more leaves, but
seed production was delayed considerably. This probably relates more to the
plant’s adaptation to their enviroment, than to adaptation due to resistance.
The susceptible population was collected from a natural environment, while
the others were collected from wheat fields.
In the third experiment the seed dormancy of the Bromus populations was
investigated. The effect of different treatments on the dormancy of the seed
was also investigated. The treatments that were applied were gibberrellic
acid, fumigation with ammonia gas and an ammonia treatment combined with
a cold treatment. Seed dormancy in all populations was short-lived and the
cold treatment was an effective way of stimulating fresh seed to germinate.
The last experiment was performed to develop a quicker method for the
evaluation of resistance in Bromus spp. In this experiment the petridish
method was investigated. Only sulfosulfuron and iodosulfuron + mesosulfuron
were used, because resistance to them was proven earlier. Different
concentrations of the herbicides were applied to the dishes with the seed and
were exposed to a cold treatment before being placed in a germination
chamber. The seed in al the treatments germinated and it was decided to let
the seed grow for two weeks in the petri dishes to observe whether the
herbicides may have a detrimental effect on the growth of the small seedlings.
After two weeks there were no differences between treatments and the
experiment was terminated. The study showed that resistance is present in some of the Bromus
populations and that there are biological differences between populations with
different degrees of resistance. However, the fact that the susceptible
population comes from a completely different environment than the other
populations, complicate matters and further studies are required to obtain a
clearer picture. / AFRIKAANSE OPSOMMING: Predikantsluis (Bromus diandrus Roth.) is ‘n onkruid wat in die meeste koringen
garsproduserende gebiede, asook in sommige vee praktyke, probleme
veroorsaak. Tot redelik onlangs (ongeveer 1995) was daar in Suid-Afrika
geen middels geregistreer wat predikantsluis in koring kon beheer nie. Nadat
sulfosulfuron en iodosulfuron + mesosulfuron vir predikantsluisbeheer in
koring geregistreer is, is die twee middels op groot skaal, en in die geval van
koring monokultuurstelsels, aanhoudend toegedien. Gedurende die afgelope
paar jaar is berigte ontvang dat beheer van predikantsluis met die middels nie
meer so doeltreffend is nie, moontlik as gevolg van onkruiddoderweerstand
wat ontwikkel het. Met die ontstaan van onkruiddoderweerstand is dit
belangrik om praktyke en maniere te vind om weerstand vinniger te bevestig
en doeltreffend te bestuur. Die doel van hierdie studie was eerstens om
weerstand in predikantsluis te bevestig en tweedens om die groei en
ontwikkeling van plante afkomstig van vermoedelike weerstandbiedende
predikantsluis populasies te vergelyk met plante uit ‘n vatbare populasie. Die
saadproduksie en dormansie van die saad is ook ondersoek asook effektiewe
metodes om dormansie te breek. Laastens is ondersoek ingestel na ‘n
vinniger manier (petribakkie metode) om weerstand te bevestig. Hieronder
volg ‘n oorsig oor die vier eksperimente wat uitgevoer is.
In die eerste proef is die mate van weerstand van drie verskillende
predikantsluis populasies bepaal, deur van die gewone potspuit metode
gebruik te maak. Daar is ook een populasie elk van Bromus pectinatus en
vermoedelik Bromus rigidus ingesluit in die studie. Die sade van die
verskillende populasies is toegelaat om te ontkiem en daarna is dit in
plastiese potjies geplant en in ‘n glashuis geplaas totdat die drie tot vier
blaarstadium bereik is. Die plante is daarna gespuit met die volgende vier
middels: haloksifop-R-metielester (Gallant Super), imasamoks (Cysure),
iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor), teen sewe
konsentrasies elk, nl. teen die aanbevole dosis, asook teen een kwart van,
een helfte van, twee keer, vier keer en agt keer die aanbevole dosis. Na ses
weke is die persentasie oorlewendes en die droëmassa van die plante bepaal. Resultate het getoon dat die drie predikantsluis populasies
verskillende grade van weerstand teen die twee sulfonielureums
(sulfosulfuron en iodosulfuron + mesosulfuron) toon, dit wil sê van geen tot
matig tot sterk weerstandbiedend. Daar is egter geen weerstand teen
haloksifop-R-metielester (Gallant Super) en imasamoks (Cysure)
waargeneem nie. Die B. rigidus populasie het sterk weerstand of toleransie
(natuurlike weerstand) teen die sulfonielureum middels getoon.
In die tweede proef is saad van dieselfde Bromus populasies ontkiem en
oorgeplant in plastiese potte gevul met 3 liter riviersand om die groei en
ontwikkeling en saadproduksie van die plante te evalueer. Die aantal blare
per plant en hoogte van die plante is weekliks bepaal totdat die plante
reproduktief geraak het. Hierna is die metings gestaak om te voorkom dat die
saadproduksie van die plante benadeel word. Die resultate het getoon dat die
twee weerstandbiedende predikantsluis populasies vinniger groei as die
vatbare populasie en ook langer plante vorm, terwyl die vatbare populasie
vinniger en meer blare vorm, maar langer neem om saad te vorm. Hierdie
waarnemings hou egter waarskynlik meer verband met die oorsprong van die
populasies as met die graad van weerstandbiedendheid. Die vatbare
populasie is versamel in natuurlike veld vêr van enige landerye terwyl die
ander populasies almal uit graanlande afkomstig is.
In die derde proef is saaddormansie van die Bromus populasies ondersoek.
Daar is ook ondersoek ingestel na verskillende behandelings om dormansie
te breek. Die behandelings wat toegepas is, is ‘n gibberelienesuur
behandeling teen verskillende konsentrasies, beroking met ammoniak vir
verskillende tye en ‘n ammoniak behandeling tesame met ‘n koue
behandeling. Die resultate het getoon dat saaddormansie van die Bromus
populasies van korte duur is, maar dat kouebehandeling effektief is om
ontkieming van vars saad te stimuleer.
Die vierde proef is uitgevoer om vas te stel of daar vinniger evaluasiemetodes
is vir die evaluasie van weerstand in Bromus spp., deur van die petribakkie
metode gebruik te maak. In hierdie proef is slegs die middels iodosulfuron + mesosulfuron (Cossack) en sulfosulfuron (Monitor) gebruik, omdat daar ‘n
mate van weerstand teen hulle waargeneem is in die eerste proef. Die
middels is teen verskillende konsentrasies in petribakkies gevoeg, tesame
met die sade en toe blootgestel aan ‘n kouebehandeling voordat dit in ‘n
ontkiemingskabinet geplaas is vir ontkieming. Die sade in al die behandelings
het ontkiem en daar is besluit om die saailinge uit die ontkiemingskabinet te
haal en vir twee weke te laat groei sodat daar bepaal kon word of die middels
‘n effek op die groei van die plantjies het. Na twee weke kon geen verskil in
die groei van die plantjies waargeneem word nie en die proef is beëindig.
Die studie het getoon dat daar wel weerstand in sommige van die Bromus
populasies voorkom, en dat biologiese verskille voorkom tussen
predikantsluis populasies met verskillende grade van weerstand. Die feit dat
die vatbare populasie uit ‘n heeltemaal verskillende omgewing kom as die
ander populasies, maak definitiewe afleidings moeilik. Daar sal opvolgstudies
uitgevoer moet word om van die onduidelikhede op te klaar.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17354 |
| Date | 04 1900 |
| Creators | Fourie, Johan Hendrik Petrus |
| Contributors | Pieterse, P.J., University of Stellenbosch. Faculty of Agrisciences. Dept. of Agronomy. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | Afrikaans |
| Detected Language | Unknown |
| Type | Thesis |
| Format | ix, iii, 88 leaves : ill. |
| Rights | University of Stellenbosch |
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